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A theoretical analysis of the orientation and alignment of the rotational angular momenta of the reactants and products of the Li + HF(v = 0, j = 3) → LiF(v, j) + H reaction at a collision energy of E = 0.317 eV is performed. The polarization of the angular momentum of the molecules involved in the reaction is based on the technique of spherical tensor operators (state multipoles). Quantum-mechanical calculations of the S-matrix of the reaction are carried out using the wave packet method. In particular, the influence of the orientation of the angular momentum of the HF reactant on the differential cross section is examined. It is shown that the contribution to the differential cross section comes only from be reactants with an angular momentum perpendicular to the reaction plane. In addition, the angular dependence of the orientation and alignment of the angular momenta of the reaction products are examined. It is shown that, for an isotropic distribution of reactant molecules, the orientation of the angular momenta of the products differs from zero only in the direction perpendicular to the reaction plane. Different experimental geometries, based on radiation enhanced multiphoton ionization, are proposed to detect the predicted effects. [ABSTRACT FROM AUTHOR]

A path-integral Monte Carlo (PIMC) method has been used to investigate the dynamics of the Ar dimer and trimer with temperature. Energy and radial distributions are compared with estimates obtained from alternative approaches based on the calculation of the discrete and continuum rovibrational spectra of the two systems. The analysis of the Ar case reveals that the system only evolves between the equilibrium configuration and the breaking of the ArAr bond. This feature thus differs from the situation observed for the trimer in a previous study where the existence of a collinear isomer between the equilateral arrangement and the predissociative ArAr structure was manifested. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The state-to-state differential cross sections for some atom + diatom reactions have been calculated using a new wave packet code, MAD-WAVE3, which is described in some detail and uses either reactant or product Jacobi coordinates along the propagation. In order to show the accuracy and efficiency of the coordinate transformation required when using reactant Jacobi coordinates, as recently proposed [J. Chem. Phys.2006, 125, 054102], the method is first applied to the H + D2reaction as a benchmark, for which exact time-independent calculations are also performed. It is found that the use of reactant coordinates yields accurate results, with a computational effort slightly lower than that when using product coordinates. The H++ D2reaction, with the same masses but a much deeper insertion well, is also studied and exhibits a completely different mechanism, a complex-forming one which can be treated by statistical methods. Due to the longer range of the potential, product Jacobi coordinates are more efficient in this case. Differential cross sections for individual final rotational states of the products are obtained based on exact dynamical calculations for some selected total angular momenta, combined with the random phase approximation to save the high computational time required to calculate all partial waves with very long propagations. The results obtained are in excellent agreement with available exact time-independent calculations. Finally, the method is applied to the Li + HF system for which reactant coordinates are very well suited, and quantum differential cross sections are not available. The results are compared with recent quasiclassical simulations and experimental results [J. Chem. Phys.2005, 122, 244304]. Furthermore, the polarization of the product angular momenta is also analyzed as a function of the scattering angle. [ABSTRACT FROM AUTHOR]

A quantum chemistry-like approach has been recently developed in our group to deal with HeN–BC doped helium clusters, where the BC dopant is a conventional diatomic molecule. The central idea is to consider the He atoms as “electrons” while the B and C atoms play the role of the nuclei in standard electronic structure calculations. The procedure provides energies and wavefunctions allowing to perform spectral simulations and, hence, making feasible to do proper comparisons with current experiments. However, because of the large difference of masses of He and electrons, and also to the replacement of Coulomb potentials by molecular interactions, it is worthy to assess to what extent the approximations involved in this model (decoupling of orbital angular momenta of the He atoms from the BC rotation and adiabatic separation of the BC stretch versus the He motions) lead to accurate results. In this work we address these issues on the 4He2–Br2(X) system, containing a couple of bosonic He atoms for which variational calculations can be performed. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

The energy of the Ar trimer has been investigated in terms of the temperature for T ≤ 1 K, by means of a path-integral Monte Carlo calculation and a variational approximate method based on the use of the interparticle distances. The comparison reveals that the values of the energy obtained via both methods are in a fairly good agreement. [ABSTRACT FROM AUTHOR]

The title reaction is studied using a quasi-classical trajectory method for collision energies between 0.1 meV and 10 eV, considering the vibrational excitation of $ {\rm H}_2^+ $ H 2 + reactant. A new potential energy surface is developed based on a Neural Network many body correction of a triatomics-in-molecules potential, which significantly improves the accuracy of the potential up to energies of 17 eV, higher than in other previous fits. The effect of the fit accuracy and the non-adiabatic transitions on the dynamics are analysed in detail. The reaction cross section for collision energies above 1 eV increases significantly with the increasing of the vibrational excitation of $ {\rm H}_2^+ $ H 2 + ( $ v^{\prime} $ v ′ ), for values up to $ v^{\prime} $ v ′ =6. The total reaction cross section (including the double fragmentation channel) obtained for $ v^{\prime} $ v ′ =6 matches the new experimental results obtained by Savic, Schlemmer and Gerlich [Chem. Phys. Chem. 21 (13), 1429.1435 (2020). doi:]. The differences among several experimental setups, for collision energies above 1 eV, showing cross sections scattered/dispersed over a rather wide interval, can be explained by the differences in the vibrational excitations obtained in the formation of $ {\rm H}_2^+ $ H 2 + reactants. On the contrary, for collision energies below 1 eV, the cross section is determined by the long range behaviour of the potential and do not depend strongly on the vibrational state of $ {\rm H}_2^+ $ H 2 + . In addition in this study, the calculated reaction cross sections are used in a plasma model and compared with previous results. We conclude that the efficiency of the formation of $ {\rm H}_3^+ $ H 3 + in the plasma is affected by the potential energy surface used. [ABSTRACT FROM AUTHOR]