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The BOUND program calculates the bound states of a complex formed from two interacting particles using coupled-channel methods. It is particularly suitable for the bound states of atom-molecule and molecule-molecule Van der Waals complexes and for the near-threshold bound states that are important in ultracold physics. It uses a basis set for all degrees of freedom except $R$, the separation of the centres of mass of the two particles. The Schr\"odinger equation is expressed as a set of coupled equations in $R$. Solutions of the coupled equations are propagated outwards from the classically forbidden region at short range and inwards from the classically forbidden region at long range, and matched at a point in the central region. Built-in coupling cases include atom + rigid linear molecule, atom + vibrating diatom, atom + rigid symmetric top, atom + asymmetric or spherical top, rigid diatom + rigid diatom, and rigid diatom + asymmetric top. Both programs provide an interface for plug-in routines to specify coupling cases (Hamiltonians and basis sets) that are not built in. With appropriate plug-in routines, BOUND can take account of the effects of external electric, magnetic and electromagnetic fields, locating bound-state energies at fixed values of the fields. The related program FIELD uses the same plug-in routines and locates values of the fields where bound states exist at a specified energy. As a special case, it can locate values of the external field where bound states cross scattering thresholds and produce zero-energy Feshbach resonances. Plug-in routines are supplied to handle the bound states of a pair of alkali-metal atoms with hyperfine structure in an applied magnetic field., Comment: One of two parallel papers that document the MOLSCAT, BOUND and FIELD programs, which use closely related theoretical methods but serve different purposes. This paper and arXiv:1811.09584 therefore have substantial text overlap

International audience; Phosphorus bearing molecules have been discovered in the circumstellar and interstellar media. Modeling their abundance accurately requires computations of rate coefficients induced by collision with He and H 2 (i.e., the most abundant gaseous components). These calculations may be carried out by first determining highly accurate potential energy surface (PES) and cross sections. In this paper, we present the first PES of the CP(X 2 Σ +)-He(1 S) van der Waals collisional complex. The ab initio interaction potential was performed using the explicitly correlated restricted coupled cluster approach with simple, double, and perturbative triple excitation (RCCSD(T)−F12) in connection with the augmented-correlation consistent−polarized valence triple-ζ Gaussian basis set (aug-cc-pVTZ). The potential presents two minima of −18.62 cm −1 and −18.72 cm −1. From the PES obtained, we have computed state-to-state excitation cross sections of CP due to collision with He for energies up to 500 cm −1. Rotational transitions involving the fine-structure levels of the CP molecule were treated with a recoupling technique based on the scattering matrix calculated with the exact quantum mechanical close coupling method. Discussions on the propensity rules between the fine-structure levels were made and we found that the Δj = ΔN transitions are favored with respect to the Δj ≠ ΔN ones. The data presented in this paper may have a great impact on the accurate determination of the CP abundance in space.

Contains fulltext : 35248.pdf (Publisher’s version ) (Closed access) Rovibronic energy levels and properties of the Br(P-2)-HCN complex were obtained from three-dimensional calculations, with HCN kept linear and the CN bond frozen. All diabatic states that correlate to the P-2(3/2) and P-2(1/2) states of the Br atom were included and spin-orbit coupling was taken into account. The 3 x 3 matrix of diabatic potential surfaces was taken from the preceding paper (paper 1). In agreement with experiment, we found two linear isomers, Br-NCH and Br-HCN. The calculated binding energies are very similar: D-0 = 352.4 cm(-1) and D-0 = 349.1 cm(-1), respectively. We established, also in agreement with experiment, that the ground electronic state of Br-NCH has vertical bar Omega vertical bar = ((1)/(2)) and that Br-HCN has a ground state with vertical bar Omega vertical bar = ((3)/(2)), where the quantum number, Omega, is the projection of the total angular momentum, J, of the complex on the intermolecular axis R. This picture can be understood as being caused by the electrostatic interaction between the quadrupole of the Br(P-2) atom and the dipole of HCN, combined with the very strong spin-orbit coupling in Br. We predicted the frequencies of the van der Waals modes of both isomers and found a direct Renner-Teller splitting of the bend mode in Br-HCN and a smaller, indirect, splitting in Br-NCH. The red shift of the CH stretch frequency in the complex, relative to free HCN, was calculated to be 1.98 cm(-1) for Br-NCH and 23.11 cm(-1) for Br-HCN, in good agreement with the values measured in helium nanodroplets. Finally, with the use of the same potential surfaces, we modeled the Cl(P-2)-HCN complex and found that the experimentally observed linear Cl-NCH isomer is considerably more stable than the (not observed) Cl-HCN isomer. This was explained mainly as an effect of the substantially smaller spin-orbit coupling in Cl, relative to Br.

This paper presents a theoretical study of the bound states of the open-shell OH radical in its ground electronic state(X2Π) interacting with n Ar atoms, for n from 4 to 12. After freezing the geometry of the Arn cage or subunit at the equilibrium structure (preceding paper), we carry out nonadiabatic five-dimensional quantum dynamics calculations on two coupled potential energy surfaces, using an extension of the method previously applied to closed-shell ArnHFclusters [J. Chem. Phys. 103, 1829 (1995)]. The method is based on a discrete variable representation (DVR) for the translational motion of OH relative to Arn, combined with a finite basis representation of the OH hindered rotation and electronic structure, including spin–orbit effects. The pattern of OH hindered rotor levels in clusters is similar to that in Ar–OH itself, though extended over three to four times the energy range for n=4 to 9. Ar12OH has a nearly spherical shell of Ar atoms around the OH, so the anisotropic splitting is very small. For n=10 and 11, the anisotropy may be viewed as arising from holes in an otherwise spherical shell, and the resulting patterns of hindered rotor levels are inverted versions of those for Ar2OH and Ar–OH.

New multireference, configuration‐interaction potential energy surfaces are reported for the interaction of Ar with the BH radical in its ground (X 1Σ+) and first excited (A 1Π) electronic states. These potential energy surfaces are then used with an adiabatic bender model for the calculation of the vibrational energy levels of the ArBH van der Waals complex in its ground and first excited singlet electronic states. Comparison of vibrational energies calculated using this adiabatic bender model with computed exact vibrational energies indicates that the former provides a very useful description of the bound levels of the ArBH complex. A qualitative discussion of the expected features in the A 1Π−X 1Σ+ electronic spectrum of ArBH is also presented, to facilitate comparison with the experimental ArBH spectrum reported in the following paper [E. Hwang and P. J. Dagdigian, following paper, J. Chem. Phys. 101, 2903 (1994)]. The most strongly bound ArBH(A) levels, with Ar–BH separations less than in the ground ...

In this second paper (II) of a series, we report our picosecond time-resolved studies of the state-to-state rates of vibrational predissociation in iodine–rare gas (van der Waals) clusters. Particular focus is on the simplest system, I2He, which serves as a benchmark for theoretical modeling. Comparisons with I2Ne and I2H2 are also presented. The results from measurements made in real time are compared with those deduced from linewidth measurements, representing a rare example of a system studied by both methods under identical conditions and excited to the same quantum (v [script '] i ) states. The discrepancies are discussed in relation to the origin of the broadening and preparation of the state. The rates as a function of v [script '] i display a nonlinear behavior which is examined in relation to the energy-gap law. The measured absolute rates and their dependence on v [script '] i are compared with numerous calculations invoking classical, quantum, and semiclassical theories. In the following paper (III in this series), the cluster size of the same system, I2Xn, is increased (n=2–4) and the dynamics are studied.

High resolution ir data on weakly bound OCOHF complexes formed in a slit supersonic expansion reveal a progression of extremely low frequency vibrational levels associated with the bending of the OCO–HF hydrogen bond. In a previous paper [J. Chem. Phys. 93, 7716 (1990)], we presented a spectroscopic analysis of the fundamental, combination and hot bands observed, corresponding to transitions between vlbend=00, 11, 20, 22, and 31, where vlbend denotes quanta of OCOHF skeletal bend excitation with l units of vibrational angular momentum. In this paper, we analyze the rotationally resolved data in terms of the rigid bender formalism of Hougen, Bunker and Johns to determine an explicit angular potential, V(θ), for the OCOHF complex in both the HF ground (vHF=0) and vibrationally excited (vHF=1) state.The OCOHF ground state (vHF=0) potential is dominated by quartic and sextic angular terms, and thus is surprisingly shallow with respect to the bending angle. This quasilinear vibrational behavior is characterize...

In a recent paper [J. Chem. Phys. 2005, 122, 124318], a full-dimensional quantum method, designed to efficiently compute the rovibrational states of triatomic systems with long-range interactions, was applied to the benchmark Li - (H 2 ) ion-molecule system. The method incorporates several key features in order to accurately represent the rovibrational Hamiltonian using only modestly sized basis sets: (1) exact analytical treatment of Coriolis coupling; (2) a single bend-angle basis for all rotational states; (3) phase space optimization of the vibrational basis; (4) G 4 symmetry adaptation of the rovibrational basis. In this paper, the same methodology is applied for the first time to a van der Waals complex system, He(H 2 ). As in the Li - (H 2 ) study, all of the rovibrational bound states, and a number of resonance states, are computed to very high accuracy (1/10 000 of a wavenumber or better). Three different isotopologues are considered, all of which are found to have a single bound state with a very low binding energy. Several extremely long-lived Feshbach resonances are also reported.

In an earlier paper, 1 we detailed the current status of the comparison between experimentally observed reaction crosssections and product HF(v,J) vibration-rotation state populations and corresponding results obtained using quantum scattering theory on current state-of-the-art potential energy surfaces (PESs) for the title reaction. More recently, a paper from the Skodje group has appeared 2 that offers an even more up-todate evaluation and an excellent overview. The latter paper points out that remaining experimental-theoretical differences are unlikely to arise from the treatment of the quantum dynamics or through contributions of the 2 P1/2 excited state of fluorine, which is in line with what we said in ref 1. Reference 2 also emphasizes that differences in the HF product vibrational populations likely arise from an incorrect exothermicity of the theoretical PES and that there seem to be errors in this PES in the region of the product-channel FH‚‚‚H van der Waals well. The main emphasis of ref 2 was to introduce corrections to the Stark and Werner 3 PES, which is the best global threedimensional (3D) PES presently available, and to improve its descriptions of the exothermicity and of the FH‚‚‚H van der Waals well. Although great progress has been made on both the experimental and theoretical (PES and reaction dynamics) fronts in the past 20 years, there remain differences between the theoretical and experimental findings suggesting that small errors (ca. 0.5-1.0 kcal mol -1 ) remain in even the very best current

In this special issue of CAMOP/Physica Scripta we would like to present a picture of the state-of-the-art in the field of the dynamics of molecular systems. It contains a collection of papers submitted in association with the most recent MOLEC meeting (MOLEC XVI), which was held in September 2006 in Levico Terme (Italy) to celebrate the 30th anniversary of the MOLEC conference series. The series of biennial European Conferences on the Dynamics of Molecular Systems (MOLEC) started in 1976, when the first meeting was held in Trento (Italy). Successive conferences were organized in Brandbjerg Højskole (Denmark, 1978), Oxford (UK, 1980), Nijmegen (The Netherlands, 1982), Jerusalem (Israel, 1984), Aussois (France, 1986), Assisi (Italy, 1988), Bernkastel-Kues (Germany, 1990), Prague (Czech Republic, 1992), Salamanca (Spain, 1994), Nyborg Strand (Denmark, 1996), Bristol (UK, 1998), Jerusalem (Israel, 2000), Istanbul (Turkey, 2002) and Nunspeet (The Netherlands, 2004). This is the second time that Physica Scripta has hosted a special issue dedicated to MOLEC. The previous issue ( Physica Scripta (2006) 73 C1–C89) was edited by Steven Stolte and Harold Linnartz following the MOLEC 2004 conference. Following the philosophy of CAMOP, we have asked invited speakers to summarize important problems in their research area, with the objective of setting forth the current thinking of leading researchers in atomic, molecular and optical physics. This comprises discussions of open questions, important new applications, new theoretical and experimental approaches and also predictions of where the field is heading. In addition to being authoritative contributions of acknowledged experts, we hope that the papers also appeal to non-specialists as each work contains a clear and broad introduction and references to the accessible literature. The present special issue comprises 17 papers, which are arranged according to the following topics: theoretical and experimental studies of molecular collisions and chemically reactive systems (papers by Toennies, Cavalli et al, Varandas, Nyman, Allan et al, Liu et al, Boxford et al); cooling and alignment of molecular systems (papers by Kumarappan et al, van de Meerakker et al); photon–matter interactions, spectroscopy and photodissociation (papers by Fárník and Buck, Golan et al, Borghesani et al, Coreno et al); theory of complex systems (papers by Villarreal et al, Bodo et al, Yurtsever and Calvo). The final contribution concerns the dynamics of systems of biological relevance (paper by Denicke et al). The paper by Toennies, one of the founding fathers of the MOLEC conference and winner of the MOLEC award in 1996, presents a comprehensive account of the experimental developments in the field of low energy collisions over the last 30 years, and provides a short outlook on how the most recent cooling and ultra cooling techniques (helium droplets and electro-magnetic laser traps) could open up new perspectives in the field of chemical reaction dynamics. Cavalli et al present a theoretical interpretation of overlapping resonances in the reactive cross section for the benchmark reaction F + H2→HF + H, explained by the formation of a short-lived state located in the transition state region and of a van der Waals metastable state in the exit valley. The subject of accurate ab initio calculations for potential energy surfaces is addressed by Varandas in a paper describing suitable modelling strategies to obtain intermolecular potentials at near spectroscopic resolution. In the following paper, Nyman gives an overview of how thermal rate constants for polyatomic chemical reactions can be calculated from first principles: the reaction H2 + CH3→CH4 + H is used as an example and theoretical results are compared with experimental ones. The `uncharted territory' of collision dynamics at the gas–liquid interface is explored in the pioneering contribution by Allan et al, in which experimental results on the reactivity of O atoms with long chain liquid hydrocarbons are interpreted with the aid of molecular dynamics calculations. The contribution of Liu et al shifts towards the reactivity of charged systems, by presenting results of crossed beam experiments on the reaction dynamics of ethylene with OD+ and D2O+ ions. Boxford et al continue with an experimental and theoretical study of the systematics of multiply-charged anion fragmentation in dianion–cation contact ion pairs. The next two contributions present the latest findings in the field of cooling and alignment of molecular systems. Kumarappan et al provide an overview of adiabatic and non-adiabatic laser-induced alignment of linear and asymmetric top molecules. van de Meerakker and Meijer discuss the state-of-the-art of Stark deceleration of OH radicals and the prospects for future applications of such tools in scattering experiments are presented. The third section of this issue comprises spectroscopy and photodissociation studies. Fárník and Buck discuss the photodissociation of HBr molecules in three different cluster environments: pure hydrogen bonded (HBr) n clusters, large van der Waals bonded HBr·Ar n and HBr·(H2O) n clusters. Differences in the photofragmentation of rovibrationally excited methylamine and propyne molecules are taken as an example by Golan et al to demonstrate the importance of vibrationally mediated photodissociation for understanding energy flows in molecular systems. A study of the IR luminescence in excited and weakly bound rare gas complexes is reported in the contribution by Borghesani et al. Coreno et al discuss the generation of core hole states by soft x-ray absorption of molecules by presenting results on the visible and UV fluorescence decay from H2O, NH3 and CH4 molecules following core electron excitation and by proposing a mechanism of molecular dissociation. The fourth section includes three theoretical contributions. In the first one, by Villarreal et al, the simulation of IR spectra of molecules solvated in atomic clusters is reviewed by presenting a method to obtain energies and wave functions for systems composed of a molecular impurity immersed in He clusters. Bodo et al continue with an application of variational and diffusion Monte Carlo calculation procedure to the `solvation' of molecular and atomic ions in small He clusters. Yurtsever and Calvo describe the influence of a central point defect on the structure of 2D clusters consisting of point charge particles that are confined by an isotropic trap. Finally, Denicke et al review the imaging technique of single-beam and multi-beam two-photon laser-scanning microscopy for biomedical research by showing applications to the study of cell metabolism via NADH imaging. We are grateful to all the authors who participated with their contributions to this issue. We thank Physica Scripta for providing us with a platform for the publication of the MOLEC special issue and we hope that such a recently established tradition will continue to bring to readers new insights into the advances in the field of molecular dynamics.

In this paper we present a study of the response of the bacterial photosynthetic reaction center to femtosecond pulses. We demonstrate that an analysis based on the density matrix can be used to give a description of recent pump - probe experiments. It is shown that apart from the usual relaxation process corresponding to a unit change of vibrational quantum number, relaxation corresponding to a second-order process also has to be taken into account. This conclusion is based on the apparent absence of oscillations at the blue side of the spectrum. Assuming that the relaxation rates of the oscillations is dominated by van der Waals forces, it is shown that the values for the relaxation rates of this pigment-protein complex can be understood in terms of a disordered solid model. Comparing the first-order relaxation rate to the second-order relaxation rate, we obtain an approximate upper mass limit of the oscillator. This then yields an estimate of the mass of the oscillator which is found to be about 10 au. The analysis proposed in this paper should apply to other systems as well, where again a mass estimate can be obtained. 16 refs., 6 figs.

In a previous paper (http://www.phys.uri.edu/people/nightingale/publications.html, chem-ph/9406003) we developed a form of variational trial wave function and applied it to van der Waals clusters: five or less atoms of Ar and Ne modeled by the Lennard-Jones potential. In addition, we tested the trial functions for a hypothetical, light atom resembling Ne but with only half its mass. We did not study atoms such as He with larger de Boer parameters, i.e., systems in which the zero point energy plays a more important role relative to the potential energy. This is the main purpose of the present paper. In fact, we study clusters to the very limit where the zero-point energy destroys the ground state as a bound state. A simple picture of this un-binding transition predicts the power law with which the energy vanishes as the de Boer parameter approaches its critical value and the power of the divergence of the the size of the clusters in this limit. Our numerical results are in agreement with these predictions., Comment: text and figures TeX form, 4 pages

The long-range interactions among two- or three-atom systems are of considerable importance in the cold and ultracold research areas for many-body systems. For an ion and an atom, the long-range interaction potential is dominated by the induction (or polarization) potential resulting from the (classical) effect of the ion's electric field on the atom and the leading term of the induction potential is much stronger than the (quantum mechanical) dispersion (or van der Waals) interaction. The present paper focuses on the long-range interaction of the $\mathrm{Li}(2\phantom{\rule{0.16em}{0ex}}^{2}S)\ensuremath{-}\mathrm{Li}(2\phantom{\rule{0.16em}{0ex}}^{2}S)\ensuremath{-}{\mathrm{Li}}^{+}(1\phantom{\rule{0.16em}{0ex}}^{1}S)$ system, to see what changes this induction effect (originating in the electric field of the ${\mathrm{Li}}^{+}$ ion) yields in the long-range additive and nonadditive interactions of this three-body system. Using perturbation theory for energies, we evaluate the coefficients ${C}_{n}$ in the potential energy for the three well-separated constituents, where $n$ refers to the corresponding order in inverse powers of distance, obtaining the additive interaction coefficients ${C}_{4}, {C}_{6}, {C}_{7}, {C}_{8}, {C}_{9}$ and the nonadditive interaction coefficients ${C}_{7}, {C}_{9}$. The obtained coefficients ${C}_{n}$ are calculated with highly accurate variationally generated nonrelativistic wave functions in Hylleraas coordinates. Our calculations may be of interest for the study of three-body recombination and for constructing precise potential energy surfaces. We also provide precise evaluations of the long-range potentials for the two-body $\mathrm{Li}(2\phantom{\rule{0.16em}{0ex}}^{2}S)\ensuremath{-}{\mathrm{Li}}^{+}(1\phantom{\rule{0.16em}{0ex}}^{1}S)$ system. For both the two-body and three-body cases, we provide results for the like-nuclei cases of $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$.

In the present paper, the ground state van der Waals potential of the Radon dimer is described by the Tang-Toennies potential model, which requires five essential parameters. Among them, the two dispersion coefficients C 6 and C 8 are estimated from the well determined dispersion coefficients C 6 and C 8 of Xe2. C 10 is estimated by using the approximation equation that C 6 C 10 / C 8 2 has an average value of 1.221 for all the rare gas dimers. With these estimated dispersion coefficients and the well determined well depth D e and R e the Born–Mayer parameters A and b are derived. Then the vibrational energy levels of the ground state radon dimer are calculated. 40 vibrational energy levels are observed in the ground state of Rn2 dimer. The last vibrational energy level is bound by only 0.0012 cm−1.

The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg = He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species.

Often, experimental spectra with only partially resolved rotational structure are observed. In such cases, determination of potential energy curves for the corresponding electronic states might be not as reliable as in the high resolution studies. In this paper, we estimate the uncertainties of the potential energy curve parameters, obtained from spectra with partially or not resolved rotational structure, where both frequencies and intensities are fitted. As an example, recently reported excitation spectrum of the B 3 1(5 3 P 1 ) ← X 1 0 + (5 1 S 0 ) electronic transition in CdAr van der Waals complex is used. Two types of Morse functions are used to model the excited state potential, but method can be readily extended to more complex potential functions. It is shown, that for reliable estimation of the uncertainties of given potential function one should take into account the possible variation of the transition dipole moment function.

In this paper, a four-dimensional potential energy surface (PES) for the Ne-D2O complex is constructed theoretically. The calculations are carried out at CCSD(T) level with large basis sets augmented with mid-bond functions. The PES includes explicit dependence on the ν 2 symmetric bending coordinate Q 2 of the D 2 O molecule. Two vibrationally averaged potentials in the ground and first excited bending states are obtained respectively. Using these two potentials we calculate the bound states of the complexes. The theoretical rovibrational transition frequencies for three bands: П(1 11 ,ν 2 = 1)←Σ0 00 , Σ(1 11 ,ν 2 = 1)←Σ0 00 and n = 1, Σ(0 00 ,ν 2 = 1)←Σ0 00 are predicted and generally in good agreement with the experimental observed values.

An extension of the van der Waals hadron resonance gas (VDWHRG) model which includes in-medium thermal modification of hadron masses, the TVDWHRG model, is considered in this paper. Based on the 2+1 flavor Polyakov Linear Sigma Model(PLSM) and the scaling mass rule for hadrons we obtain the temperature behavior of all hadron masses for different fixed baryon chemical potentials $\mu_{B}$. We calculate various thermodynamic observables at $\mu_{B}=0$ GeV in TVDWHRG model. An improved agreement with the lattice data by TVDWHRG model in the crossover region ($T\sim 0.16-0.19$ GeV) is observed as compared to those by VDWHRG and Ideal HRG (IHRG) models. We further discuss the effects of in-medium modification of hadron masses and VDW interactions on the transport coefficients such as shear viscosity ($\eta$), scaled thermal ($\lambda/T^{2}$) and electrical ($\sigma_{el}/T$ conductivities in IHRG model at different $\mu_{B}$, by utilizing quasi-particle kinetic theory with relaxation time approximation., Comment: 17 pages, 13 figures

We investigate collisional shifts of spectral lines involving excited hydrogenic states, where van der Waals coefficients have recently been shown to have large numerical values when expressed in atomic units. Particular emphasis is laid on the recent hydrogen 2S-4P experiment (and an ongoing 2S-6P experiment) in Garching, but numerical input data are provided for other transitions (e.g., involving S states), as well. We show that the frequency shifts can be described, to sufficient accuracy, in the impact approximation. The pressure related effects were separated into two parts, (i) related to collisions of atoms inside of the beam, and (ii) related to collisions of the atoms in the atomic beam with the residual background gas. The latter contains both atomic as well as molecular hydrogen. The dominant effect of intra-beam collisions is evaluated by a Monte-Carlo simulation, taking the geometry of the experimental apparatus into account. While, in the Garching experiment, the collisional shift is on the order of 10 Hz, and thus negligible, it can decisively depend on the experimental conditions. We present input data which can be used in order to describe the effect for other transitions of current and planned experimental interest., Comment: 26 pages; 2 figures; this is part 2 of a series of two papers; part 1 carries article number 075005, while part 2 carries article number 075006 in the journal (online journal version has been rectified)

16 pags., 11 figs., 3 tabs. -- This paper is part of the JCP Special Collection in Honor of Women in Chemical Physics and Physical Chemistry, A new spin-averaged potential energy surface (PES) for non-reactive O2(ςg-3) + O2(ςg-3) collisions is presented. The potential is formulated analytically according to the nature of the principal interaction components, with the main van der Waals contribution described through the improved Lennard-Jones model. All the parameters involved in the formulation, having a physical meaning, have been modulated in restricted variation ranges, exploiting a combined analysis of experimental and ab initio reference data. The new PES is shown to be able to reproduce a wealth of different physical properties, ranging from the second virial coefficients to transport properties (shear viscosity and thermal conductivity) and rate coefficients for inelastic scattering collisions. Rate coefficients for the vibrational inelastic processes of O2, including both vibration-to-vibration (V-V) and vibration-to-translation/rotation (V-T/R) energy exchanges, were then calculated on this PES using a mixed quantum-classical method. The effective formulation of the potential and its combination with an efficient, yet accurate, nuclear dynamics treatment allowed for the determination of a large database of V-V and V-T/R energy transfer rate coefficients in a wide temperature range., This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA17030100) and the National Natural Science Foundation of China through Grant Nos. 11372325 and 91116013. M.B. acknowledges the FIS2017-84391-C2-2-P Spanish grant for fundings.

The knowledge of accurate rate coefficients for collisional excitation of molecules by the abundant species like He, H2 and H are required for modeling the atmospheric conditions of interstellar medium. The present paper aims to study the transitions in the lowest twelve rotational levels in the ground vibrational state of CO+(X 2Σ+) by collisions with helium atoms. We computed ab initio two-dimensional potential energy surface of 2Σ+/2A' symmetry for the He-CO+ van der Waals complex asymptotically correlating to He(1S) + CO+(X 2Σ+) using restricted coupled-cluster method with perturbative treatment of triples employing augmented correlation consistent polarized valence quadruple-ζ basis set. Rovibrational bound states of He-CO+ complex for total angular momentum, J = 0 have been computed. The state-to-state rotational excitation cross sections are performed by close-coupling method up to center of mass collision energy of 2000 cm−1. The corresponding rate coefficients are obtained up to a temperature of 300 K.

The assignment of the rovibrational spectra of molecule-Ne complexes is always a challenge to study van der Waals systems, since they usually exhibit behavior intermediate between free rotor and rigid rotor. In this paper, the microwave and infrared spectra of CH3F-Ne, a model system for symmetric-top-atom dimer, were firstly predicted and analyzed based on the four-dimensional ab initio intermolecular potential energy surfaces(PESs), which explicitly incorporate the v 3(C—F) stretch normal model coordinate of the CH3F monomer. Analytic three-dimensional PESs were obtained by least-squares fitting vibrationally averaged interaction energies for v 3(CH3F)=0 and 1 to the Morse/long-range(MLR) potential function for symmetry top impurity with atom model. These PESs fitting to 2340 points have root-mean-square(RMS) deviations of 0.07 cm–1, and require only 167 parameters. Based on the analytical vibrationally averaged PESs, the rovibrational energy levels were calculated by employing Lanczos algorithm, with combined radial discrete variable representation and parity-adapted angular finite basis representation. Based on the wavefunction analysis and comparison of CH3F-Ne with CH3F-He and CH3F-Ar complexes, the bound states were assigned. Spectral parameters for CH3F-Rg(Rg: rare gas, Rg=He, Ne, Ar) complexes were fitted and discussed. Temperature dependent transition intensities for CH3F-Ne were also reported and analyzed. The complete microwave and infrared spectra information for CH3F-Ne made it possible to provide important guidance for future experimental spectroscopic assignments.

The focus of this paper is the weakly-bound H2O⋯O2 van der Waals dimer. The global minimum has an electronic dissociation energy of 0.70 kcal mol−1 at the spin unrestricted CCSD(T) level of theory (UCCSD(T)) in conjunction with a correlation consistent quadruple-zeta basis set augmented with diffuse functions on all heavy atoms, denoted haQZ (i.e., cc-pVQZ for H and aug-cc-pVQZ for O). Eleven other stationary points are also characterized at the UCCSD(T)/haQZ level of theory, all of which lie within 0.5 kcal mol−1 of the global minimum and have at least one imaginary frequency (ni ⩾ 1). The spin unrestricted MP2 method (UMP2) yields very similar structures and energies for the twelve stationary points. However, the UMP2 vibrational frequencies provide a qualitatively different description of the potential energy surface (more than a single minimum), of the frequency shifts upon complexation and of the resulting infrared intensities of the complex. The UCCSD(T)/haQZ computations indicate only one of the twelve H2O⋯O2 structures is a minimum and that it exhibits appreciable infrared intensity for one of the lowest energy intermolecular vib rational modes, unlike the related H2O⋯N2 system.

The fabrication of nanoscale oscillators working in the gigahertz (GHz) range and beyond has now become the focal center of interest to many researchers. Motivated by this issue, this paper proposes a new type of nano-oscillators with enhanced operating frequency in which both the inner core and outer shell are electrically charged. To this end, molecular dynamics (MD) simulations are performed to investigate the mechanical oscillatory behavior of ions, and in particular chloride ion, tunneling through electrically charged carbon nanotubes (CNTs). It is assumed that the electric charges with similar sign and magnitude are evenly distributed on two ends of nanotube. The interatomic interactions between carbon atoms and van der Waals (vdW) interactions between ion and nanotube are respectively modeled by Tersoff-Brenner and Lennard-Jones (LJ) potential functions, whereas the electrostatic interactions between ion and electric charges are modeled by Coulomb potential function. A comprehensive study is conducted to get an insight into the effects of different parameters such as sign and magnitude of electric charges, nanotube radius, nanotube length and initial conditions (initial separation distance and velocity) on the oscillatory behavior of chloride ion-charged CNT oscillators. It is shown that, the chloride ion frequency inside negatively charged CNTs is lower than that inside positively charged ones with the same magnitude of electric charge, while it is higher than that inside uncharged CNTs. It is further observed that, higher frequencies are generated at higher magnitudes of electric charges distributed on the nanotube.

The special properties of ionic liquids are due to the simultaneous presence of Coulombic and van der Waals forces. Evaluation of their interaction strengths is a basic work for explaining the macroscopic physical properties of ionic liquids, understanding the molecular dynamics and microstructure of ionic liquids, and assessing the binding force induced by ions in biological systems. In this paper, a modified Coulomb's law was constructed to calculate the average electrostatic force in ionic liquids through treating an ionic liquid molecule as two charges separated by some organic groups and taking these organic groups as an organic molecule. The modified Coulomb's law was verified with the surface tension data of 117 non-ionic liquids and 153 ionic liquids. According to the modified Coulomb's law, the average strengths of the electrostatic and van der Waals interactions between a pair of cation-anion in the 153 ionic liquids were almost equal, which were about 20 pN.

Modeling the physical conditions of interstellar medium requires knowledge of accurate rate coefficients for collisional excitation of molecules by the abundant chemical species like He and H2. The present paper aims to study transitions in the low rotational levels in the ground vibrational state of CN+(X 1Σ+) by collisions with helium atoms. We computed ab initio two-dimensional (rigid-rotor) potential energy surface for the He-CN+ van der Waals collision complex using multi-reference configuration interaction method employing augmented correlation consistent polarized valence quadruple-ζ basis set. The bound-states of the van der Waals complex are obtained by coupled channel approach. The state-to-state rotational excitation cross sections are computed by exact close-coupling quantum mechanical formalism up to center of mass collision energy of 2000 cm−1. The corresponding rate coefficients are obtained up to 300 K temperature.

In this paper we have estimated the Van der Waals dipole-dipole and dipole-quadrupole energies in alkali halides. The calculations are based on the theory of electronic polarizabilities proposed by Ruffa. The magnitudes of Van der Waals energies in alkali halides are found to be larger by a factor of 2 to 4 than those reported by earlier investigators. The reasons for the differences between results of other investigators and the current work have been discussed with special emphasis on electronic polarizabilities of ions. It is pointed out that the larger magnitudes of the Van der Waals energies obtained in the present paper are in conformity with the studies on phase transition and lattice-dynamical behavior of alkali halides.

This paper contains a review of experimental and theoretical work concerned with the selectivity of collision-induced vibrational relaxation and proposes a new method for achieving selectivity of chemical reaction. The paper is based on the Debye Award Lecture and emphasizes work in the author's laboratory. There are many ways in which a molecule can be made reactive and many ways in which energy can be transferred within one molecule and between colliding molecules. In this paper the author focuses attention on what must be considered only a first step in learning about the selectivity of those elementary dynamical processes that influence the selectivity of a chemical reaction. Specifically, the author considers the characteristics of vibrational energy redistribution arising from atom-polyatomic molecule collisions and from the dissociation of an atom-polyatom van der Waals molecule.

This paper contributes to the theory of the long-ranged attractive polarization force between a neutral atom and a crystalline solid surface in the non-relativistic limit. The first two terms in the asymptotic expansion of the polarization energy are used to define an atom-solid potential of the form V(pol) = -C(Z - Zo) to the (-3) power. The constant C appearing in this expression is known from the earlier work of E. M. Lifshitz. The present paper gives a theory of the position of the 'reference plane,' Z(o), which is important in applications to physisorption. An explicit expression for Z(o) is first derived for atoms interacting with a jellium metal and with an insulating crystal consisting of atoms which interact via dipole-dipole forces. These model calculations are then incorporated into a computation of the polarization energies of rare gas atoms physisorbed on noble metal surfaces. The computed energies are found to be consistent with observed adsorption energies.

A simple semiclassical theory of the van der Waals potential, which uses no empirical constants, was proposed and tested on atom–atom systems in an earlier paper [J. Chem. Phys. 66, 1496 (1977)]. In a following paper [J. Chem. Phys. 68, 5501 (1978)] it was successfully applied to the prediction of the radial v0(R) and anisotropic parts v2(R) of the van der Waals potential expanded as V(R,γ)=v0(R)+v2)R)× P2(cos γ) (R is the distance between centers of mass and γ is the angle between R and the molecular axis) of He–H2 and Ne–H2 for which all the necessary ab initio input data were available. In the present paper the method is applied to the heavier systems Ar–H2, Kr–H2, and Xe–H2 for which the ab initio data are not available. The dispersion terms were estimated using the precise combining rule described in II. The anisotropic Born–Mayer parameters for the repulsive potentials were estimated by successive application of the Gilbert–Smith combining rules. The necessary input was the ab initio repulsive aniso...

We present an alternative optical emission spectroscopy method to measure the plasma electron density from the difference of widths of two Balmer series hydrogen lines ( H α and H β ), especially convenient for non-thermal plasmas since with this method, there is no need to know either the gas temperature or the van der Waals contribution to the Lorentzian part of the line. In this paper it has been assumed that the part of full width at half maximum due to Stark broadening can be determined with the approximation of Lorentzian line shape. The method has been applied to the determination of the electron density in an argon microwave-induced plasma maintained at atmospheric pressure, and comparison with the results obtained using other diagnostic methods has been done.

This paper is an overview of our recent experimental investigations of the RgI2 van der Waals complexes, Rg = He, Ar, Kr, performed by means of laser induced fluorescence spectroscopy, optical-optical double resonance and supersonic molecular beam techniques. Spectroscopic parameters of these complexes in the E0 g + ion-pair state, such as binding energies and several spectroscopic constants, have been determined. Most likely, the potential energy surfaces of the all RgI2(E) complexes under study present T-shaped minima. Vibrational and electronic predissociations of the RgI2(E) complexes were analyzed. Relative contributions of the different electronic predissociation channels and vibrational distributions of the decay products were determined. Possible mechanisms of the complexes decay are suggested and discussed.

We study many-atom van der Waals (vdW) forces arising from reversible atom–field interactions in cavity quantum electrodynamics by using a dressed-state approximation. In the most general case, a single-mode Dicke model for atoms, sharing an arbitrary number of excitations, placed in an imperfect cavity, has been developed that leads to the vdW potential of such a system. As special cases, we consider the single-excitation Dicke model and also the case of one atom in the presence of multi-photon excitation inside the cavity. In most of the paper, it is assumed that the atoms are distributed symmetrically with respect to the mode structure. This will decouple all asymmetric states, allowing us to ignore them throughout our calculations. The impact of asymmetric states is taken into account for a system wherein one atom, freely placed in a cavity, together with n − 1 equally-coupled atoms, is interacting with the cavity field. By assuming broadened Lorentzian modes instead of sharp ones, the cavity imperfections have been added to the calculations. The position dependence of the effective Rabi frequency is studied for the example of a planar cavity.

Non-thermal plasmas sustained at atmospheric pressure are considered as a very promising technology for different purposes, in which the knowledge of the gas temperature is an important issue. In this paper, the gas temperatures of different argon microwave (2.45 GHz) plasma torches were determined by using different Optical Emission Spectroscopy techniques. Thus, they were estimated through the analysis of N 2 + (B-X) and OH(A-X) molecular spectra. On the other hand, a method based on the measurement of the van der Waals broadening of 588.99 nm Na I line was employed, and the temperatures obtained from it were compared to the rotational temperatures derived from N 2 + (B-X) and OH(A-X) rotational bands. A reasonable good agreement was found between the values of temperatures obtained by using the 588.99 nm Na I line and those obtained from N 2 + rotational band.

用量子化学耦合簇CCSD/aug-cc-pVTz等方法，计算了稀有气体分子，作了电子密度差及图形，通过图形解读了范德华作用的本质和形成机理。提出了范德华作用的量子化学图景是：原子或分子配对的电子云球相碰，由于Pauli互斥，电子云球变形，形成了电子一定程度的回避，同时产生了一定程度的电子共享，达到吸引和排斥的平衡，从而构成了范德华力。认为范德华作用的本质也是一种波函数在起作用，并因此构成了核之间吸引共享电子，也是一种化学作用力。 In this paper, coupled-cluster CCSD/aug-cc-pVTz and related quantum chemistry methods are employed to calculate rare gas molecules and plot figures of electron density differences, the nature and formation mechanism of van der Waals interaction are interpreted graphically. We propose a quantum chemistry picture for van der Waals interac- tion: In the process of the collision of paired electron cloud of atoms or molecules, electron cloud balls deform due to Pauli repulsion effect, and a certain degree of electron avoidance as well as electron sharing are formed. The van der Waals force is the consequence of the equilibrium between the attraction and repulsion. We believe that the nature of van der Waals effect is acting of wavefunction, which results in the internuclear shared electron, so van der Waals ef- fect can also be seen as a kind of chemical force.

In the ultracold gases of alkali-earth (like) atoms, a new type of Feshbach resonance, i.e., the orbital Feshbach resonance (OFR), has been proposed and experimentally observed in ultracold $^{173}$Yb atoms. When the OFR of the $^{173}$Yb atoms occurs, the energy gap between the open and closed channels is smaller by two orders of magnitudes than the van der Waals energy. As a result, quantitative accurate results for the low-energy two-body problems can be obtained via multi-channel quantum defect theory (MQDT), which is based on the exact solution of the Schr$\ddot{{\rm o}}$dinger equation with the van der Waals potential. In this paper we use the MQDT to calculate the two-atom scattering length, effective range, and the binding energy of two-body bound states for the systems with OFR. With these results we further study the clock-transition spectrum for the two-body bound states, which can be used to experimentally measure the binding energy. Our results are helpful for the quantitative theoretical and experimental researches for the ultracold gases of alkali-earth (like) atoms with OFR., Comment: 11 pages, 6 figuers

The paper presents how to study the thermal vibration of a double-walled carbon nanotube (DWCNT) by using a model of double-Euler beams, together with the law of energy equipartition, with the energy of van der Waals interaction between layers taken into consideration. The basic finding of the study is the relation, derived via the model of double-Euler beams and the law of energy equipartition, between the temperature and the root-of-mean-squared (RMS) amplitude of the thermal vibration at any cross section of the DWCNT. The molecular dynamics simulations of thermal vibration of the DWCNT in argon atmosphere show that the model of double-Euler beams can predict the RMS amplitude of the thermal vibration of the DWCNT reasonably well.

The bonding of the beryllium diatomic molecule (Be2) in the ground state is exclusively made from the electron correlation effect. Unlike the ordinary van der Waals bond, where the electron correlation of the dispersion type makes weak bond energy (De) at large bond distance (Re), the BeBe bond is surprisingly strong with De = 830 cm−1 and Re = 245 pm. This paper presents in an analytical way the different electron correlation effects with the corresponding spectroscopic data.

Resonant frequencies and the associated vibrational modes of multiwall carbon nanotubes are studied in this paper. The analysis is based on a multiple-elastic beam model, considering intertube radial displacements and the related internal degrees of freedom. Especially, van der Waals interaction is modified considering both all interaction between each layers in multi-wall carbon nanotubes and curvature effect. The results show that modified van der Waals interaction could significantly affect the natural frequencies of multi-walled carbon nanotubes. In particular, non-coaxial intertube resonance will be excited at the higher resonant frequencies of multiwall carbon nanotubes.

Radiation transport in high intensity discharge lamps (HID) can be calculated using ray tracing technique solving directly radiative transfer equation. The calculations reported in the present paper have been performed by applying basic equations of radiation theory in local thermodynamic equilibrium (LTE) plasma and assuming the cylindrical symmetry. Neither axial variations nor convention have been taken into account. Experimental values for pressure and temperature profiles are used to calculate the radiative and photometric characteristics of the lamp. Neutral Van der Waals and charged particles Stark broadening have been included in the line broadening.

In this paper we investigate a variationally stable procedure for multipolar dynamic polarizabilities calculation as well as the two- and three-body van der Waals coefficients of the hydrogen atom. This approach provides precise, fast convergent values for real and imaginary frequency-dependent 2 L -pole dynamic polarizabilities. Highly accurate two- and three-body van der Waals dispersion coefficients are calculated from dynamic polarizabilities at imaginary photon frequencies. The present approach is also precise for higher interaction orders. The results are compared with previous calculations found in the literature.

This book contains papers on physical and chemical phenomena of solid clusters. The papers cover the atomic and electronic structure, dynamics, stability, fragmentation, optical properties, interaction with adsorbates, astrochemistry and van der Waals forces of clusters. (LSP)

In this paper we employ two distinct approaches - all-electron \textit{ab initio} method and the spherical jellium background model- within time dependent density functional theory to calculate the long range dipole-dipole dispersion coefficient (van der Waals coefficient) $C_{6}$ of sodium atom clusters containing even number of atoms ranging from 2 to 20 atoms. The dispersion coefficients are obtained via Casimir-Polder relation. All the calculations are carried out with local density approximation for exchange-correlation energy functional. These two sets of results are compared to assess the accuracy of jellium based results and to ascertain the effect of detail ionic structure of the clusters on the van der Waals coefficient., Comment: 15 pages including 2 figures. To be published in Journal of Computational Methods in Science and Engineering

Desorption of vibrationally excited CO molecules from NaCl surface has been studied more than a decade ago in experiments of Chang and Ewing [H.C. Chang, G.E. Ewing, Chem. Phys. 139 (1989) 55]. Surprisingly, the desorption process was found to be inefficient (longer than 102 s) although the van der Waals type complex CO–NaCl has enough energy to break the weak CO–NaCl bond (i.e., to get the CO molecules off the solid surface). The present paper gives a clear theoretical explanation of this phenomenon. Namely, our calculations based on complex scaling show that the vibrational excitation energy of CO is transferred into its rotational motion, while the coupling between the rovibrational degrees of freedom of CO and the surface is suppressed. Thereby, the highly rotationally excited CO molecule is trapped on the solid surface practically forever and forms a bound state in the continuum. This type of trapping mechanism is not specific to the interaction between adsorbed molecules and the surfaces of ionic crystals only, and might be applicable to other systems and to other type of experiments.

In this paper, the interesting case of two overlapping resonances which occur in the F + H-2 reaction is revisited emphasizing the role of the total angular momentum. We show that molecular rotations of the triatomic collision complex are responsible for the alignment of a short-lived compound state, localized in the transition state region of the potential energy surface, with an exit-channel van der Waals metastable state. The changes induced by the total angular momentum on both positions and lifetimes make the resonances to interfere and produce quantum oscillating structures in integral and differential cross-sections.

This paper reports the formation and characterization of large (Ar) n , (N2) n , and mixed binary (Ar) n (N2) m van der Waals clusters produced at room temperature in the process of supersonic expansion. The average cluster size is determined by the buffer gas induced beam-broadening technique. For both Ar and N2 clusters, power variations of the average cluster size $$ \ifmmode\expandafter\bar\else\expandafter\=\fi{n} $$ with the gas stagnation pressure P 0 give size scaling as $$ \ifmmode\expandafter\bar\else\expandafter\=\fi{n} \propto P^{{1.9}}_{0} $$ . The average cluster sizes of argon vary from 2950 to more than 30900 atoms per cluster with the argon gas stagnation pressures ranging from 4 to 14 bars, and of nitrogen vary from 600 to more than 10400 molecules per cluster with the nitrogen gas stagnation pressures ranging from 8 to 38 bars. The mixed binary (Ar) n (N2) m cluster is produced by supersonic expansion of an Ar–N2 mixture. The large mixed binary (Ar) n (N2) m clusters with the average sizes n + m between 1000 and 16000 are obtained. In coexpansion of Ar–N2 mixture, we find that the argon concentration becomes higher in the beam than before the expansion. This finding is discussed and may be helpful for further insight into the phenomenon of clustering.

The rotamer approximation states that protein side-chain conformations can be described well using a finite set of rotational isomers. This approximation is often applied in the context of computational protein design and structure prediction to reduce the complexity of structural sampling. It is an effective way of reducing the structure space to the most relevant conformations. However, the appropriateness of rotamers for sampling structure space does not imply that a rotamer-based energy landscape preserves any of the properties of the true continuous energy landscape. Specifically, because the energy of a van der Waals interaction can be very sensitive to small changes in atomic separation, meaningful van der Waals energies are particularly difficult to calculate from rotamer-based structures. This presents a problem for computational protein design, where the total energy of a given structure is often represented as a sum of precalculated rigid rotamer self and pair contributions. A common way of addressing this issue is to modify the van der Waals function to reduce its sensitivity to atomic position, but excessive modification may result in a strongly nonphysical potential. Although many different van der Waals modifications have been used in protein design, little is known about which performs best, and why. In this paper, we study 10 ways of computing van der Waals energies under the rotamer approximation, representing four general classes, and compare their performance using a variety of metrics relevant to protein design and native-sequence repacking calculations. Scaling van der Waals radii by anywhere from 85 to 95% gives the best performance. Linearizing and capping the repulsive portion of the potential can give additional improvement, which comes primarily from getting rid of unrealistically large clash energies. On the other hand, continuously minimizing individual rotamer pairs prior to evaluating their interaction works acceptably in native-sequence repacking, but fails in protein design. Additionally, we show that the problem of predicting relevant van der Waals energies from rotamer-based structures is strongly nonpairwise decomposable and hence further modifications of the potential are unlikely to give significant improvement.

This paper deals with the understanding at a first-principles level of the nuclear quadrupole interaction (NQI) parameters of solid chlorine, bromine and iodine as well as the intermolecular binding of these molecules in the solid. The electronic structure investigations that we have carried out to study these properties of the solid halogens are based on the Hartree-Fock Cluster approach using the Roothaan variational procedure with electron correlation effects included using many-body perturbation theory with the empty orbitals used in the perturbation theory investigations for the excited states. The results of our investigations provide good agreement with the measured NQI parameters primarily from the Hartree-Fock one electron wave-functions with many-body effects making minor contributions. The binding (dissociation) energies for the molecules with the solid state environment on the other hand arises from intermolecular many body effects identified as the Van der Waals attraction with one-electron Hartree-Fock contribution being repulsive in nature.

This paper reviews research on helium clusters (of up to 20 atoms) and molecular hydrogen clusters (of up to 17 molecules) weakly bound by van der Waals forces to a light chromophore molecule such as OCS, N2O, CO2, or CO. Such clusters form in supersonic gas jets and are studied through the spectrum of the particular chromophore used. It is found that as the cluster grows, its rotational frequency increases (the effective moment of inertia decreases) starting from a certain number of atoms (molecules) attached. Also, in CO-based clusters a nearly free rotation of the chromophore molecule was observed. Experimental studies of such clusters are reviewed, as are those of the N2–CO and CO–CO complexes in which both monomers nearly freely rotate. The relation of these rotations to the superfluidity of helium and hydrogen is discussed, and comparisons are made with spectroscopic experiments on chromophores and hydrogen clusters in liquid helium nanodroplets.

The paper presents a theoretical approach of the long-range interaction between an atomic system in an arbitrary quantum level and dispersive dielectric surface in thermal equilibrium at temperature T(Gorza et. al, 2006) This theoretical study is performed within the frame work of the quantum-mechanical linear response - using generalised susceptibilities for both atom and e.m. field -and allows one to derive a general expression for the atomic energy shift in front of any material surfaces.