Molecular Physics

We present a new model for the rotation-vibration motion of pyramidal XY 3 molecules, based on the Hougen-Bunker-Johns approach. Inversion is treated as a large-amplitude motion, while the small-amplitude vibrations are described by linearized stretching and bending coordinates. The rotation-vibration Schro¨dinger equation is solved variationally. We report three applications of the model to 14 NH 3 using an analytic potential function derived from high-level ab initio calculations. These applications address the J ¼ 0 vibrational energies up to 6100 cm, the J 4 2 energies for the vibrational ground state and the 2 , 4 , and 2 2 excited vibrational states, and the J 4 7 energies for the 4 þ 2 vibrational state. We demonstrate that also for four-atomic molecules, theoretical calculations of rotation-vibration energies can be helpful in the interpretation and assignment of experimental, high-resolution rotationvibration spectra. Our approach incorporates an optimum inherent separation of different types of nuclear motion and thus remains applicable for rotation-vibration states with higher J values where alternative variational treatments are no longer feasible.

This paper describes the local enhancement of quadratic nonlinear optical properties of granular gold nano-structures and their effect on nonlinear molecules deposited on them. A two-photon excitation microscope has been employed in order to detect second harmonic generation with a sub-microscopic resolution. Surface-SHG from the gold granular structures exhibits intense signals in sub-micrometer sized regions randomly localized on the surface. The spatial distribution and polarization state of these signals provides significant information on the underlying physics of the local enhancement effect. We show furthermore that the signal from nonlinear chromophores deposited on these substrates is strongly enhanced with factors up to 2xi0 3 , before decaying within a few seconds. Quantitative measurements indicate a significant local electromagnetic contribution to the molecular enhancement. Molecular damage and possible metalmolecule interactions are analyzed in order to explain the magnitude and the fast decay of this effect.

The relaxation kinetics of succinonitrile in the plastic crystalline phase has been investigated between 250 and 320 K by transient optical Kerr effect with femtosecond pulses. Three different noninstantaneous contributions to the signal time profile have been identified. The fastest one is a subpicosecond decay, attributed to the relaxation of the damped librational and torsional vibrations of the molecules. The intermediate decay time, ranging from 4 ps at 323 K to 30 ps at 250 K, is interpreted as due to rotations of the trans molecules about the shortest inertia axis which bring the molecule from one cube diagonal to another. The slowest decay time ranges from 28 ps at 323 K to 190 ps at 250 K and agrees very well with previous measurements with different experimental techniques. This decay is interpreted as due mostly to rotational motions of the gauche molecules jumping from one equilibrium position to another in the unit cell. The activation energy for the two processes is 3....

This paper examines the transformation of copyright limitations on the free use of works for educational and research purposes in the context of distance learning. As technology advances, educational institutions increasingly use digital learning tools which include copyrighted material. The European Union has continuously tried to harmonise copyright laws across the Member States by adopting directives, such as the Information Society Directive, and providing exceptions for using works for educational purposes. However, national legislators have been given a great deal of freedom, resulting in divergent implementation in the Member States. Lithuania, in line with the EU law, included an exception to the copyright law to allow the use of small parts of works for educational and scientific research purposes. However, the law did not explicitly address digital use and cross-border education, which caused difficulties during the COVID-19 pandemic. To meet the challenges of the digital age, in 2019, the EU adopted the Digital Market Directive, which entered into force in May 2022 and provided for a mandatory copyright exception for educational purposes. This directive aimed to modernise copyright law by facilitating the use of works in digital and cross-border education.  Despite the updates to the copyright exceptions, several problematic aspects remained. The Directive restricts the digitization of a whole textbook or the use of whole works for educational purposes. The updated legal framework is considered modern, but it has only partially addressed the challenges posed by technological advances. The article therefore stresses the need for continuous assessment of the digitization and hosting of distance learning materials and copyright infringement.

The disaccharide trehalose has shown outstanding anti-aggregation properties for proteins, which are highly important for the possibility to treat neurodegenerative diseases, such as Alzheimer's and Huntington's disease. However, the role and mechanism of trehalose for such stabilising effects are still largely unknown, partly because a direct structural picture of how trehalose organises around proteins in an aqueous system is missing. Here we compare small-angle neutron scattering (SANS) data on myoglobin in aqueous solutions of either sucrose or trehalose, in order to investigate their effect on protein-protein interactions. We find that both trehalose and sucrose induces a well-defined protein-protein distance, which could explain why these inhibit protein-protein interactions and associated protein aggregation. It does not however explain the superior antiaggregation effect of trehalose and suggests that the local solvent structures are highly important for explaining the protein stabilisation mechanism. In a broader perspective, these findings are important for understanding the role of sugars in biological stabilisation, and could provide a structural explanation for why trehalose is a promising candidate for the treatment of neurodegenerative and other protein aggregation related diseases.

Quantum calculations on the VSD of Kv1.2 (3Lut pdb coordinates) show several water molecules move into the VSD when the sign of the electric field goes from positive intracellularly to negative (closed). The protein backbone remains essentially immobile; S4 does not move vertically with respect to the other transmembrane segments, but may have minimal horizontal motion (parallel to the membrane surface, were the membrane included in the calculation); side chain rearrangements, however, change some intramolecular distances. We have calculated the dipole moments of the optimized structures for several cases, as well as the structures of the water clusters (these calculations:18 water molecules, 373 atoms from the protein, from the 2nd to the 4th arginine in S4, and the complementary sections of S1, S2, and S3). Rotating two water molecules in the cluster (closed conformation) sufficed for a significant change in dipole (in most calculations, counting the dipole for the entire system; dipole changes with state as well, %5 D for the open configuration, approximately an order of magnitude more when closed, suggesting dipole shift is part of the sensing mechanism). Several energy minima were determined; the closed configurations were several kT lower in energy than open configurations. The water behavior resembled a phase change, with finite DV (volume) in its overall shift in structure with changes in electric field; there is more than one energy minimum, but the change in water density is unambiguous, although the water is not ordered in either case. Gating is coupled to water via a proton shift in the lower section of the VSD (see our other abstract).

Observation of strong deviation of photoluminescence excitation curve from absorption curve specially at lower wavelength range, below 450 nm in case of small sized toxic metal free InP based core-alloy-shell quantum dots hints towards interesting exciton dynamics. PL quantum yield (PLQY) has been observed to be dependent on the excitation wavelength. Monitoring the bleach dynamics employing femtosecond ultrafast pump-probe technique it could be shown that the rise-time increases with decrease in pump excitation wavelength from 100 fs for 550 nm excitation to 220 fs for 430 nm pump/excitation. Therefore exciton cooling takes longer time for lower wavelength excitation and thus the exciton becomes more prone to get trapped. About two fold enhancement in magnitude of normalized bleach signal at the band edge (~0.1 (for 430nm excitation) to ~0.2 (for 550nm excitation)) following exciton relaxation has been observed. Thus, in comparison to lower wavelength excitation, for near band-edge pump/excitation there is higher probability of radiative exciton recombination, therefore increasing PLQY. Hot exciton trapping dynamics has been noted to be occurring at a timescale ~750 fs. From ultra-sensitive single particle measurement, magnitude of power-law exponent for both ON and OFF events remain similar to each other and the magnitude remains unaltered for different excitation wavelengths, (405 nm to 568 nm). As long as 100 s ON event could be observed making this InP based non-toxic QD quite suitable for single particle tracking etc. Interestingly, ON event truncation time has been found to increase from 6s to 16s and OFF event truncation time has been found to decrease from 11s to 5.5s, thereby exciton detrapping rate / trapping rate increases from 0.5 to nearly 3 on going from 405 nm to 568 nm excitation. Thus, as the trapping gets suppressed and detrapping gets enhanced, PLQY gets enhanced. The extent of relative decrease of PLQY value with increase in excitation energy above band-edge has been observed to be much more pronounced in CdSe based CAS QD than InP based CAS QD.

Expressions for the thermodynamic factor matrix Γ of quaternary mixtures are derived in terms of Kirkwood-Buff integrals and implemented into the massivelyparallel simulation tool ms2. To assess these expressions, a liquid-like supercritical quaternary Lennard-Jones mixture is sampled throughout its entire composition range, employing molecular dynamics in the canonical ensemble. Good agreement is found between numerical chemical potential derivatives and the results from the present Kirkwood-Buff integral expressions. Moreover, the limits of the thermodynamic factor matrix for pure, binary and ternary subsystems are discussed.

Combinatorial aspects of the Robinson-Schensted-Knuth (RSK) algorithm have been discused in the context of a Heisenberg magnetic ring with N nodes, each with the spin s. Each magnetic configuration acquires a natural interpretation as a word of the length N in the alphabet of spins, consisting of n = 2s + 1 letters. We demonstrate that the construction of n-tuple cover of the ring, with a separate copy for each letter of the alphabet of spins, allows for a transparent determination of maximal length of non-decreasing subwords. Moreover, it yields completeness of the RSK correspondence in classification of the irreducible basis of the Weyl duality between actions of unitary and symmetric groups in the space spanned on all magnetic configurations.

We investigate cooperative phenomena and superradiance for vibrational transitions in polar molecule spectroscopy when a high optical-depth (OD) sample is studied. Such cooperativity comes from the build-up of inter-particle coherence through dipole-dipole interactions and leads to the speed-up of decay process. We compare our calculation to recent work [Deiglmayr et al., Eur. Phys. J. D 65, 99 (2011)] and find very good agreement, suggesting that superradiant effects need to be included in a wide variety of ultracold molecule setups including vibrational and rotational states.

Superradiance in spin-J atoms: Effects of multiple atomic levels GUIN-DAR LIN, SUSANNE YELIN, University of Connecticut, ITAMP Harvard-Smithsonian Center for Astrophysics -We study the superradiance dynamics in a dense system of atoms each of which can be generally a spin-J particle with J an arbitrary half-integer. Using a novel formalism we derive an effective two-body master equation to study the relevant cooperative and collective effects, taking into account the coherence of transitions between different atomic levels. One direct application of such calculation is to study the superradiance, in the context of polar molecules, due to transitions between multiple excitation levels, e.g. vibrational modes.

We have created self-assembled circular chains of C 60 laterally bound to a layer of Ag atoms as a model system for characterizing fluctuations at a metal-molecule interface. STM measurements show that the Ag and C 60 sides of the interface fluctuate independently, with frequencydependent amplitudes of magnitude 0.1 nm at ∼1 Hz for the Ag edge and ∼0.01 Hz for the C 60 ring. The measured frequency spectra of the metal and molecule fluctuation amplitudes will contribute characteristic signatures to transport measurements involving such interfaces.

Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of the film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. T...

Status: To appear in JMO special issue "Ultrafast Dynamical Imaging of Matter", summer 2013. Version: RevTex 4.1 typeset version for arxiv. Time-resolved coincidence imaging of photoelectrons and photoions represents the most complete experimental measurement of ultrafast excited state dynamics, a multi-dimensional measurement for a multi-dimensional problem. Here we present the experimental data from recent coincidence imaging experiments, undertaken with the aim of gaining insight into the complex ultrafast excitedstate dynamics of 1,3-butadiene initiated by absorption of 200 nm light. We discuss photoion and photoelectron mappings of increasing dimensionality, and focus particularly on the time-resolved photoelectron angular distributions (TRPADs), expected to be a sensitive probe of the electronic evolution of the excited state and to provide significant information beyond the time-resolved photoelectron spectrum (TRPES). Complex temporal behaviour is observed in the TRPADs, revealing their sensitivity to the dynamics while also emphasising the difficulty of interpretation of these complex observables. From the experimental data some details of the wavepacket dynamics are discerned relatively directly, and we make some tentative comparisons with existing ab initio calculations in order to gain deeper insight into the experimental measurements; finally, we sketch out some considerations for taking this comparison further in order to bridge the gap between experiment and theory.

We report time-resolved fluorescence data for the anion of p-hydroxybenzylidene dimethylimidazolinone (p-HBDI), a model chromophore of the green fluorescence protein, in viscous glycerol-water mixtures over a range of temperatures, T. The markedly nonexponential decay of the excited electronic state is interpreted with the aid of an inhomogeneous model possessing a Gaussian coordinate-dependent sink term. A nonlinear least-squares fitting routine enables us to achieve quantitative fits by adjusting a single activation parameter, which is found to depend linearly on 1/T. We derive an analytic expression for the absolute quantum yield, which is compared with the integrated steady-state fluorescence spectra. The microscopic origins of the model are discussed in terms of two-dimensional dynamics, coupling the phenyl-ring rotation to a swinging mode that brings this flexible molecule to the proximity of a conical intersection on its multidimensional potential energy surface.

The relaxation times T2,' characterizing the allowed and T2'', characterizing the forbidden and coherence cross resonances, during free evolutions over the coherent pathways p = ±1 are estimated from the SECSY (Spin Echo Correlation Spectroscopy) signal of the electron-nuclear spin-coupled system in a γ-irradiated malonic acid single crystal. This is accomplished by fitting the intensities of the two main peaks in the Fourier transform of the SECSY signal reported by Lee, Patyal and Freed (J. Chem. Phys. 98, 3665 (1993)) to T2' and T2''. The values of the fitted relaxation times T2'=500 ns, T2"=50,000 ns, reveal that the relaxation via the allowed resonance is two orders of magnitude faster than that via the forbidden and cross resonances. Full details of the calculation exploiting the Liouville von Neumann equation are presented. PACS: 76.30.-v, 76.70.Dx

A full con® guration interaction study on the BH molecule is presented. The potential energy curves of 20 di erent electronic states have been calculated correlating the four valence electrons. On the two most important states, i.e. the X 1 R + and A 1 P states, a complete study has been performed. This includes the e ect of core electron correlation, estimated via truncated con® guration interaction techniques. The dissociation energy of the molecule in the two states and the height of the predissociative barrier in the A 1 P state have been determined with basis sets of increasing quality.

The short-time orientational relaxation of water is studied by ultrafast infrared pump-probe spectroscopy of the hydroxyl stretching mode (OD of dilute HOD in H 2 O). The anisotropy decay displays a sharp drop at very short times caused by inertial orientational motion, followed by a much slower decay that fully randomizes the orientation. Investigation of temperatures from 1°C to 65°C shows that the amplitude of the inertial component (extent of inertial angular displacement) depends strongly on the stretching frequency of the OD oscillator at higher temperatures, although the slow component is frequency-independent. The inertial component becomes frequency-independent at low temperatures. At high temperatures there is a correlation between the amplitude of the inertial decay and the strength of the O-D O hydrogen bond, but at low temperatures the correlation disappears, showing that a single hydrogen bond (OD O) is no longer a significant determinant of the inertial angular motion...

The problem of calculating the structure of square-well (SW) fluids in the context of non-conformal fluids is reviewed briefly. New and extensive results over a wide range of SW systems and thermodynamic states were obtained by means of the reference hypernetted chain (RHNC) integral equation. The results show that RHNC theory is in excellent agreement with the results of simulation, thus providing a reliable and fast procedure for obtaining the structure of fluids with discontinuous potentials. A few representative results are presented and compared with new Monte Carlo simulation data. The bridge functions obtained with the RHNC procedure are also compared with those calculated directly from the Monte Carlo radial distribution functions.

The interplay of the librations of a covalently bound organic adlayer with the lattice waves of an underlying semiconductor surface was characterized using helium atom scattering in conjunction with analysis by density functional perturbation theory. The Rayleigh wave dispersion relation of CH 3 -and CD 3 -terminated Si(111) surfaces was probed across the entire surface Brillouin zone by the use of inelastic helium atom timeof-flight experiments. The experimentally determined Rayleigh wave dispersion relations were in agreement with those predicted by density functional perturbation theory. The Rayleigh wave for the CH 3 -and CD 3 -terminated Si(111) surfaces exhibited a non-sinusoidal lineshape, which can be attributed to the hybridization of overlayer librations with the vibrations of the underlying substrate. This combined synthetic, experimental, and theoretical effort clearly demonstrates the impact of hybridization between librations of the overlayer and the substrate lattice waves in determining the overall vibrational band structure of this complex interface.

A combined helium atom scattering and density functional perturbation theory study has been performed to elucidate the surface phonon dispersion relations for both the CH 3 -Si( )-(1 × 1) and CD 3 -Si( )-(1 × 1) surfaces. The combination of experimental and theoretical methods has allowed characterization of the interactions between the low energy vibrations of the adsorbate and the lattice waves of the underlying substrate, as well as characterization of the interactions between neighboring methyl groups, across the entire wavevector resolved vibrational energy spectrum of each system. The Rayleigh wave was found to hybridize with the surface rocking libration near the surface Brillouin zone edge at both the M-point and K-point. The calculations indicated that the range of possible energies for the potential barrier to the methyl rotation about the Si-C axis is sufficient to prevent the free rotation of the methyl groups at a room temperature interface. The density functional perturbation theory calculations revealed several other surface phonons that experienced mode-splitting arising from the mutual interaction of adjacent methyl groups. The theory identified a Lucas pair that exists just below the silicon optical bands. For both the CH 3 -and CD 3 -terminated Si(111) surfaces, the deformations of the methyl groups were examined and compared to previous experimental and theoretical work on the nature of the surface vibrations. The calculations indicated a splitting of the asymmetric deformation of the methyl group near the zone edges due to steric interactions of adjacent methyl groups. The observed shifts in vibrational energies of the -CD 3 groups were consistent with the expected effect of isotopic substitution in this system.

Electronic energy transfer (EET) from a donor to an acceptor is an important mechanism that controls the light harvesting efficiency in a wide variety of systems, including artificial and natural photosynthesis and contemporary photovoltaic technologies. The detailed mechanism of EET at short distances or large angles between the donor and acceptor is poorly understood. Here the influence of the orientation between the donor and acceptor on EET is explored using a molecule with two nearly perpendicular chromophores. Very fast EET with a time constant of 120 fs is observed, which is at least forty times faster than the time predicted by Coulombic coupling calculations. Depolarization of the emission signal indicates that the transition dipole rotates through ca. 64 0 , indicating the near orthogonal nature of the EET event. The rate of EET is found to be similar to structural relaxation rates in the photo-excited oligothiophene donor alone, which suggests that this initial relaxation brings the dyad to a conical intersection where the excitation jumps to the acceptor.

Electronic energy transfer (EET) from a donor to an acceptor is an important mechanism that controls the light harvesting efficiency in a wide variety of systems, including artificial and natural photosynthesis and contemporary photovoltaic technologies. The detailed mechanism of EET at short distances or large angles between the donor and acceptor is poorly understood. Here the influence of the orientation between the donor and acceptor on EET is explored using a molecule with two nearly perpendicular chromophores. Very fast EET with a time constant of 120 fs is observed, which is at least 40 times faster than the time predicted by Coulombic coupling calculations. Depolarization of the emission signal indicates that the transition dipole rotates through ca. 64°, indicating the near orthogonal nature of the EET event. The rate of EET is found to be similar to structural relaxation rates in the photoexcited oligothiophene donor alone, which suggests that this initial relaxation bring...

Superconductivity in copper oxide (cuprate) high-transitiontemperature superconductors follows from the chemical doping of an antiferromagnetic insulating state. The consensus that the wavefunction of the superconducting carrier, the Cooper pair, has d x 2 -y 2 symmetry 1,2 has long been reached. This pairing symmetry implies the existence of nodes in the superconducting energy gap. Recently, a series of angle-resolved photoemission spectroscopy experiments 3-9 have revealed that deeply underdoped cuprates exhibit a particle-hole symmetric 3 superconducting-like energy gap at the momentum-space locations where the d x 2 -y 2 gap nodes are expected. Here we discuss the possibility that this phenomenon is caused by a fully gapped topological superconducting state that coexists with the antiferromagnetic order. If experimentally confirmed, this result will completely change our view of how exactly the high-temperature superconductivity state evolves from the insulating antiferromagnet. Topological arguments have been put forward to understand the robustness of the d x 2 -y 2 gap nodes in the cuprates. Therefore it was a surprise when the 'nodal gap' was experimentally observed for Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212; refs 4,5), La 2-x Sr x CuO 4 (LSCO; refs 6, 7,9), Bi 2 Sr 2-x La x CuO 6+δ (Bi2201; ref. 3) and Ca 2-x Na x CuO 2 Cl 2 (NaCCOC; ref. 8). The magnetic and transport properties of the systems manifest a nodal gap range from 'weak' antiferromagnetic (AF) insulators 3,7 to superconductors 5,7 . For example, in Bi2212, a phase diagram with a new superconducting (SC) phase appearing at the underdoped end of the SC dome has been proposed 5 . In contrast the samples showing the 'nodal gap' in ref. 3 are insulating and antiferromagnetic. However, despite these differences, relatively sharp coherence peaks were observed at the nodal gap edge in both cases . On the basis of this fact, refs 3,5 concluded that it is unlikely that such a gap is caused by disorder. However, given the fact that samples at such a low doping level can have strong phase inhomogeneity 14 , we interpret the sharp coherence peaks 3 as coming from poorly connected SC islands embedded in an insulating background. In the literature, proposals for the origin of the nodal gap range from a disorder-induced Coulomb gap 15 to spectral weight transfer due to the polaron effect 3 . However, as pointed out in refs 3,5 in both of the above scenarios one does not expect sharp coherence peaks. Motivated by refs 3,5,7 we assert that the state responsible for the nodal gap is a fully gapped SC state. Moreover, because samples exhibiting the nodal gap are found at the border between AF and SC phases we consider the possibility that such a SC state coexists with the AF order. In the rest of the paper we first tabulate all possible fully gapped SC states and organize them into different symmetry-protected topological classes (Table ). We then perform explicit calculations,

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Large local optical activity in fractal aggregates of silver nanoparticles has been observed by means of photon scanning tunneling microscopy. The effect occurs because resonant plasmon modes in random fractals can have handedness in spatial distribution of their amplitudes. In agreement with experimental observations, numerical simulations show dramatic difference in dipole-moment distributions for right-and left-circularly polarized incident light when the cluster size is comparable with or larger than the wavelength. Variations in the local parameter describing the circular intensity difference of scattered light show that fractal aggregates are characterized by broad and random distributions of chiral plasmon modes.

A ®rst step towards the development of a general, realistic potential model for per¯uoroether compounds has been to parameterize a united atom model for a short chain per¯uoroether per¯uoromethylpropyl ether (CF 3 CF 2 CF 2 OCF 3 ). The potential model takes the usual form in which separate bond bending and torsional terms describe the intramolecular interactions with the addition of van der Waals and electrostatic terms to describe the non-bonded interactions. Ab initio quantum calculations have been carried out to obtain the partial charges and intramolecular torsional and bending potentials. Phase equilibrium data were then used to optimize the van der Waals interaction parameters through Gibbs ensemble Monte Carlo simulations. The resulting model reproduces vapour±liquid equilibrium densities, the critical temperature and the critical density of per¯uoromethylpropyl ether, in good agreement with those from experiment.

We report the development of a transferable force field for the accurate modelling of perfluoroethers. The potential model takes the general form in which separate bond bending and torsional terms describe the intramolecular interactions, with the addition of van der Waals and electrostatic terms to describe the non-bonded interactions. Ab initio quantum mechanical calculations were carried out to obtain the partial charges and intramolecular torsional and bending potentials. The van der Waals interactions are described by Lennard-Jones potentials, the parameters of which are optimized to reproduce the available experimental vapour-liquid equilibrium data. An extension of the Gibbs-Duhem method was used to speed up the optimization.

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Raman scattering of the radial breathing mode of single wall carbon nanotubes was measured with a large number of different laser lines. The first and the second moments of the spectral distribution were evaluated for all recorded spectra and were found to exhibit damped oscillations with the excitation energy. The oscillations originate from the confinement of the electrons into states distributed within the van Hove singularities. An extended as well as an approximate calculation of the moments yields very good agreement with the experiments and allows to determine the diameter of the nanotube bundles. Using the approximate calculation the mean diameter and the width of the diameter distribution can be evaluated from a single Raman experiment.

Raman radial breathing-like mode (RBLM) frequencies of an infinite nanopeapods are calculated within the framework of a continuum-molecular based model. The nanotube-fullerene interaction is modeled via the Lennard-Jones interatomic potential. An analytical formulation is developed and is justified due to its good agreement with the experimental and atomistic-based results. Furthermore, we propose new relationships for the van der Waals (vdW) interaction coefficients between the atoms of this hybrid nanostructure. Numerical results are also obtained for various nanopeapods on the basis of the present formulation. The RBLM frequency upshifts are predicted for small singlewalled carbon nanotubes (SWCNTs). The frequency shifts can be adequately explained by the vdW intermolecular interactions acting between the fullerene and the SWCNTs atoms. To the best of our knowledge, a simple theoretical method which can predict the Raman RBLM frequencies of the nanopeapods with high precision has not been provided hitherto. We believe that the present study is likely to fill the gap.

A review of double resonance Raman spectroscopy is presented. Non-zone centre phonon modes in solids can be observed in the double resonance Raman spectra, in which weak Raman signals appear in a wide frequency region and their combination or overtone modes can be assigned. By changing the excitation laser energy, we can derive the phonon dispersion relations of a single nanotube. Contents 1 Introduction 2 2 General idea of resonance Raman spectroscopy 2 3 D and G bands of graphite 4 4 D band of nanotube 10 5 Other intermediate phonon modes 12 6 Summary 13 Acknowledgments 14 References 14

Carbon materials and its derivates have captured the attention of many researchers in the past. For instance, carbon nanotubes have been widely explored in the past two decades, revealing remarkable structural and physical properties. However, some physical phenomena still remain unclear. Here, a resonant Raman spectroscopy study on isotope ( 13 C) enriched carbon nanotubes will be presented. The comparative spectroscopic analysis of 13 C and 12 C carbon nanotubes is advantageous, since the variation of mass of these materials leads to modifications in the Raman spectra, such as shifts in the bands position. The influences of the laser wavelength and the isotope carbon concentration in the samples have been investigated and will also be presented.

In the absence of standard single-wall carbon nanotube samples with a well-known (n,m) population, we provide both a photoluminescence excitation (PLE) and resonance Raman scattering (RRS) analysis that together can be used to check the calculations for PLE and RRS intensities for carbon nanotubes. We compare our results with available models and show that they describe well the chirality dependence of the intensity ratio, confirming the differences between type 1 and type 2 semiconducting tubes [(2n+m)mod3]=1and2, respectively, and the existence of a node in the radial breathing mode intensity for type 2 carbon nanotubes with chiral angles between 20° and 25°.

The role of the relative motions of protons on different chain segments in the relaxation of the dipolar coupling measured in nuclear magnetic resonance experiments is considered. The relaxation of the coupling for a single intersegmental proton–proton pair is evaluated numerically, assuming that the decay of this coupling is dominated by the translational motion of the monomers. It is found that the relaxation of this coupling scales as gr(t)−5/2, where gr(t) is the mean squared relative displacement of two monomers in the melt. This scaling applies for times at which gr(t) is greater than the square of the initial separation of the two coupled protons. The effect of the short range equilibrium structure of the melt on the intersegmental relaxation is qualitatively considered by separating out, from the summation over all interactions, the interactions between the protons corresponding to the first intersegmental peak in the hydrogen–hydrogen radial distribution function. This anal...

The quinone compound 2,6-dimethoxy-1,4-benzoquinone is hydroxylated in alkaline aqueous solution with pH above 12. Electron paramagnetic resonance experiments showed that two transient radicals are formed in this reaction. The radical appearing first is assigned to a one electron reduced 2,6-dimethoxy-1,4-benzoquinone, receiving the electron from an intermediate anionic hydroxylated species. For this primary radical, all proton couplings were determined (quinoid ring protons: 1.453 G, methyl protons: 0.795 G). The density functional theory method was applied to obtain electronic and structural information of the primary radical and a solution structure is suggested. For approaching the experimental hyperfine couplings in theoretical models, it was necessary to consider effects of external polarisation arising from water molecules near one carbonyl group, and the orientation of methoxy groups towards the quinone ring. With this approach, the secondary radical formed in the hydroxylation reaction, and the transient radicals found for other biologically important quinones (including coenzymes Q) and their hydroxylated species may become accessible.

This study assesses the performance of various meta-generalized gradient approximation (meta-GGA), global hybrid, and range-separated hybrid (RSH) density functionals in capturing excited-state properties of organic chromophores and their excitedstate complexes (exciplexes). Motivated by their uses in solar energy harvesting and photoredox CO 2 reduction, we use oligo-(p-phenylenes) and their excited-state complexes with triethylamine as model systems. We focus on the fluorescence properties

When substituted benzenes become a focus of a spectroscopic study there are various well known vibrational labelling schemes present, a,b however it was shown in recent works the description of monohalobenzene vibrations in terms of benzene modes (ie. Wilson notation) is questionable in some cases. c,d A new scheme is presented which uses the motions of monofluorobenzene vibrations as a basis for labelling vibrational assignments of monosubstituted benzenes. d The scheme has been successfully applied to the ground and excited states of toluene and its deuterated-methyl group isotopologue. e,f Here we present the application of the scheme to fluorobenzene and its fully deuterated analogue. One-colour resonanceenhanced multiphoton ionization (REMPI) spectroscopy was employed in order to characterise the fluorobenzene and fluorobenzene-d 5 excited state.

In this work the interface system of the van der Waals fluid is investigated by using the density gradient theory incorporated with the mean-field theory. Based on the mean-field dividing interface generated by the Maxwell construction, we propose a highly accurate density profile model for the density gradient theory, which facilitates reliable predictions of various properties for the interface region. It is found that the local intrinsic Helmholtz free energy peaks at the interface and that the maximum difference of the normal and tangential components of the pressure tensor corresponds to the maximum of the intrinsic Gibbs free energy. It is found that the entire phase space is divided into gas-like and liquid-like regions by the single line composed of the mean-field interface and the Widom line. The two-fluid feature of the supercritical fluid is hence inherited from the coexistence region. Phase diagrams extended into the coexistence region in all the temperature-pressure-volume planes are thus completed with the solutions to the vapor-liquid equilibrium problem by the van der Waals equation of state.

Fused homodimer Colloidal Quantum Dot Molecules (CQDMs), analogous to homonuclear diatomic molecules, exhibit hybridization of the confined electronic states controlled by the neck girth at the fusion interface. Their constituent "artificial atom" CQDs manifest tunable optoelectronic properties relevant for numerous applications, including in future quantum technologies. Thus, the concept of "nanocrystal chemistry" underlying the CQDMs, greatly enriches the selection of such artificial constructs. Numerous new bright multiexcitonic configurations may form in the CQDM, unlike the multiexcitons in CQDs which are dimmed by strong non-radiative Auger recombination processes. The handle of the neck girth is found to dictate the many-body interplay in CQDMs and determines the photon purity, where in narrow neck girth (weak coupling), the CQDM acts as a multiphoton emitter, while neck filled CQDMs (strong coupling) regain single photon emission characteristics typical of the monomers. The unique attributes of the CQDMs manifesting excellent absorbing and bright tunable excitonic and multiexcitonic states highlights their relevance for potential light emitting applications. In this manuscript, we investigate the charge re-distribution upon optical excitation of various necked homodimer CQDMs using single particle emission spectroscopy. By tuning the hybridization of the electron wavefunction at a fixed center-to-center distance through controlling the neck girth, we reveal two coupling limits. On one hand a "connected-but-confined" situation where neighbouring CQDs are weakly fused to each other manifesting a weak coupling regime, and on the other hand, a "connected-and-delocalized" situation, where the neck is filled beyond the facet size leading to a rod-like architecture manifesting strong-coupling. Either coupling regimes entrust distinct optical signatures clearly resolved at room temperature in terms of photoluminescence quantum yield, intensity time traces, lifetimes, and spectra of the neutral-exciton, charged-exciton, and biexciton states. The interplay between the radiative and non-radiative Auger decays of these states, turns emitted photons from the CQDMs in the "weak-coupling" regime highly bunched unlike CQD monomers, while the antibunching is regained at the "strong-coupling' regime. This behavior correlates with the hybridization energy being smaller than the thermal energy (kT ~25meV) at the "weak-coupling" limit (∆E~5-10meV), leading to exciton localization suppressing Auger decay. In the neck-filled architectures, the larger hybridization energy (∆E~20-30meV) leads to exciton delocalization while activating the fast charged and multi-exciton Auger decay processes. This work sets an analogy for the artificial molecule CQDMs with regular molecules, where the two distinct regimes of weak-and strong-coupling correspond to ionic-or covalent-type bonding, respectively.

Two-photon polarization fluorescence microscopy is used to study the nature of the emission and nonlinear absorption dipole of single CdSe/ZnS quantum rods. Rods showed strongly polarized nonlinear excitation with sharp angular dependence, following a cos 4 (φ) functional form, in agreement with the predicted twophoton absorption process. The two-photon absorption is parallel to the emission polarization and allows high orientation selectivity in excitation to be achieved. This further demonstrates the role of single molecule measurements in unraveling basic principles of light-matter interactions otherwise masked by ensemble averaging.

The D + +H 2 reaction is investigated by means of a time independent quantum mechanical (TIQM) and a statistical quantum mechanical (SQM) methods. Differential cross sections and product rotational distributions obtained with these two theoretical approaches for collision energies between 1 meV and 0.1 eV are compared to analyze the dynamics of the process. The agreement observed between the TIQM differential cross sections and the SQM predictions as the energy increases revealed the role played by the complex-forming mechanism. The importance of a good description of the asymptotic regions is also investigated by calculating rate constants for the title reaction at low temperature.

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We measure the coherent nonlinear response of excitons in a single-layer of molybdenum disulphide embedded in hexagonal boron nitride, forming a h-BN/MoS 2 /h-BN heterostructure. Using four-wave mixing microscopy and imaging, we correlate the exciton homogeneous and inhomogeneous broadenings. We find that the exciton dynamics is governed by microscopic disorder on top of the ideal crystal properties. Analyzing the exciton ultra-fast density dynamics using amplitude and phase of the response, we investigate the relaxation pathways of the resonantly driven exciton population. The surface protection via encapsulation provides stable monolayer samples with low disorder, avoiding surface contaminations and the resulting exciton broadening and modifications of the dynamics. We identify areas localized to a few microns where the optical response is totally dominated by homogeneous broadening. Across the sample of tens of micrometers, weak inhomogeneous broadening and strain effects are observed, attributed to the remaining interaction with the h-BN and imperfections in the encapsulation process.

We present here a method for selecting optical patterns in a passive semiconductor microresonator, by using a spatial perturbation. A pattern is spontaneously generated in the system, and a switching beam causes this pattern to rotate even if the power in the switching beam is much lower than the power in the pattern. Thus, an all optical switch is realized, that operates at low light levels.

To model the double layer near an electrode, theories and simulations must include the different dielectric coefficients of the electrode, the commonly-postulated 'inner' layer, and the electrolyte. Recently, Boda et al. [D. Boda, D. Henderson, K.-Y. Chan, D.T. Wasan. Phys. Rev. E, 69, 046702, ( )] developed a technique to include inhomogeneous dielectric coefficients in arbitrary geometries in a simulation. Here, Monte Carlo simulation results based on this method are reported for the density profiles of 1:1, 2:2 and 2:1 aqueous electrolytes. The simulations include two dielectric boundaries, one from an inner layer of low dielectric coefficient and one from an uncharged metal electrode. In addition, an extension of a Poisson-Boltzmann (PB) type theory due to Onsager and Samara [L. Onsager, N.N.T. Samara. J. chem. Phys., 2, 528, (1934)] is developed and compared with our simulation results. This approach works best for 1:1 salts at low concentrations.

A comparison of the experimental momentum distribution of electrons in the highest occupied molecular orbital of N(CH,), with the electron momentum distribution of the boron-nitrogen bonding orbital of (CH,),N-BF, shows that the orbital of the complex has a larger relative density of high momentum electrons. This increase in high momentum components is associated n i t h the incrcasc in nodal surfaces in the orbital of the complex in comparison with the orbital of the amine. Qualitative agreement is seen in a comparison of the experimental momentum distributions with distributions calculated from small basis set ab initio position space orbital wave functions. The experimental results are also discussed in terms of the position apace autocorrelation function diffcrcncc M ( r ) . which is demonstrated to provide additional information concerning the orbital interactions. Thc bcn\iti\,it! and uccuracq with which (e,2e) spectroscopy can bc applied to the measurement of valence electron momentum distributions in gas-phase molecules by the present generation of high momentum resolution spectrometers has been well established during recent years.'-3 The basis of the spectroscopic technique is the observation of the high energy electron knock-out. or (e,2e), reaction. When the binding energy of electrons in a particular niolecular orbital differs sufficiently from the binding energy of othcr electrons in the molecule, it is possible to observe (e&) reactions involving essentially only the electrons of that orbital. The experimentally obtained momentum distribution p(p) is then the <phcrical average of the square modulus of the momentum space orbital wave function $ (p). In the work reported here, we have initiated an (e,2e) spectroscopic study of bonding interactions between molecules. Theoretical treatments of chemical reactivity and bonding have demonstrated that molecular interactions are often dominated by the frontier orbitals of the reactant molecule^.^ ( c . 7 ~) rpectroscopy. becnusc it can measure orbital specific momentum distributions. can provide information on such phenomena 215 clcctroii rcdihtribution and rchybridization associated with intcractiona of l'ronticr orbitals. The subject of this invcstigation is the reaction of boron trifluoride (BF,) and trimethylamine (N(CH,),) to form the electron donor-acccptor complex (CH,),N-BF,. Formation of the intermolecular bond involves the donation of charge density from the iionbondiiig highest occupied orbital of thc donor nioleculc Y(Cl13)3 to the antibonding T* lowest unoccupied orbital of the Lcni\ acid RF,. The transfer of electron density from the donor lea& to ;I nenkening of the bonds within the BF, moiety. and the complcu (CH1)?N-BF3 is therefore the product of what has been tcrmcd .in "incipient displacement r e a c t i ~n " . ~, ~ Our approach to tlic b t u d ) of the bonding interaction is to mcasurc thc niomciituiii di\tributions of two molecular orbitals: (i) the nonbonding hiyhcbt occupicd molecular orbital (HOMO) of Y(CH,), and (ii) thc boron-nitrogen bonding orbital of the complex complex (CH,),N-BF,. The orbital of ii is the HOMO of the complex and correlates with the HOMO of N(CH,), and the lowest unoccupied molecular orbital (LUMO) of BF,. By comparing the t \ r o momcntum diytributions. the rearrangement in momentum _-' Inslitutu for Ph!\ic,il Sciencc and Tcchnologq :