J. Rubayo-Soneira

Comparative configurational study for He, Ne, and Ar trimers

Helium trimer bound states are calculated by means of a variational method described in terms of atom pair coordinates and distributed Gaussian basis functions for zero total angular momentum. To show the feasibility of this method, we also apply it to the calculation of the first vibrational levels of the Ar3 and Ne3 clusters. Special emphasis is made on the study of the possible Efimov behavior of the first excited state found in the 4He3 trimer. Geometrical configurations of the ground and first excited states of these rare gas trimers have been exhaustively studied owing to the proper symmetry of the coordinates chosen.

Quasiclassical dynamics of the I2–Ne2 vibrational predissociation: A comparison with experiment

The vibrational predissociation dynamics of the I2(B,v)–Ne2 complex is investigated for several vibrational levels of I2, using a quasiclassical trajectory approach. The time evolution of the population of nascent I2 fragments is calculated. A model is proposed which reproduces the results of the classical trajectories, and allows to obtain the lifetimes associated with the dissociation of the two van der Waals (vdW) bonds. The classical lifetimes are higher in general than the experimental ones of Zewail and co‐workers [J. Chem. Phys. 97, 8048 (1992)]. The classical method appears to overestimate mechanisms of energy redistribution between the modes, which slow down the dissociation of the cluster. However, the behavior of the lifetimes with the initial iodine vibrational excitation is in very good agreement with experiment. A sequential path of fragmentation of the two weak bonds via direct predissociation is found to dominate, producing I2(B,v–2)+2Ne fragments. Although with smaller probability, altern...

Vibrational predissociation of I2Ne. A quasiclassical dynamical study

Abstract A quasiclassical trajectory method is applied to study the vibrational predissociation of the I 2 (B) … Ne van der Waals system. A potential surface for the complex is proposed and used in the calculations which is fitted with a quantum model in order to reproduce the experimental lifetimes available. The classical results are found to overestimate statistical energy redistribution mechanisms which slow down the predissociation process. The classical calculations, however, predict a behavior of the lifetime versus the initial iodine vibrational level in good agreement with the experimental data.

A theoretical investigation on the spectrum of the Ar trimer for high rotational excitations.

A detailed study of the rovibrational spectrum of the Ar trimer is performed by means of an exact hyperspherical coordinate (HC) method and a variational approach based on distributed Gaussian functions (DGFs) to describe the interparticle distances. The good agreement observed between the energy levels obtained with both procedures for high values of the total angular momentum (J=15 and 20) reveals the quality of the DGF method to describe the rotation of the title system. Rotational constants for the lowest bound states, obtained as averages for each vibrational state, have been obtained and compared to previous results. A detailed analysis of density probability functions obtained by means of the HC approach for rovibrational states at J=0 and 20 shows close similitudes thus supporting the vibration-rotation separation adopted within the DGF scheme for the Ar(3) system.

Large Shift and Small Broadening of Br2 Valence Band upon Dimer Formation with H2O: An Ab Initio Study

Valence electronic excitation spectra are calculated for the H(2)O···Br(2) complex using highly correlated ab initio potentials for both the ground and the valence electronic excited states and a 2-D approximation for vibrational motion. Due to the strong interaction between the O-Br and the Br-Br stretching motions, inclusion of these vibrations is the minimum necessary for the spectrum calculation. A basis set calculation is performed to determine the vibrational wave functions for the ground electronic state and a wave packet simulation is conducted for the nuclear dynamics on the excited state surfaces. The effects of both the spin-orbit interaction and temperature on the spectra are explored. The interaction of Br(2) with a single water molecule induces nearly as large a shift in the spectrum as is observed for an aqueous solution. In contrast, complex formation has a remarkably small effect on the T = 0 K width of the valence bands due to the fast dissociation of the dihalogen bond upon excitation. We therefore conclude that the widths of the spectra in aqueous solution are mostly due to inhomogeneous broadening.

Transformation from angle-action variables to Cartesian coordinates for polyatomic reactions

The transformation from angle-action variables to Cartesian coordinates is an important step of the semiclassical description of bimolecular collisions and photofragmentations. The basic reason is that dynamical conditions corresponding to molecular beam experiments are ideally generated in angle-action variables, whereas the classical equations of motion are ideally solved in Cartesian coordinates by standard numerical approaches. To our knowledge, this transformation is available in the literature only for atom-diatom arrangements. The goal of the present work is to derive it for diatom-polyatom ones. The analogous transformation for any type of arrangement may then be straightforwardly deduced from that presented here.The transformation from angle-action variables to Cartesian coordinates is a crucial step of the (semi) classical description of bimolecular collisions and photo-fragmentations. The basic reason is that dynamical conditions corresponding to experiments are ideally generated in angle-action variables whereas the classical equations of motion are ideally solved in Cartesian coordinates by standard numerical approaches. To our knowledge, the previous transformation is available in the literature only for triatomic systems. The goal of the present work is to derive it for polyatomic ones.

An ab Initio Calculation of the Valence Excitation Spectrum of H2O ··· Cl2: Comparison to Condensed Phase Spectra †

Valence electronic excitation spectra are calculated for the H(2)O...Cl(2) dimer using state-of-the art ab initio potentials for both the ground and the valence excited states, a basis set calculation of the ground state nuclear wave function, and a wave packet analysis to simulate the dynamics on the excited state surface. The peak of the H(2)O...Cl(2) dimer spectrum is blue-shifted by 1250 cm(-1) from that of the free Cl(2) molecule. This is less than the value previously estimated from vertical excitation energies but still significantly more than the blue shift in aqueous solution and clathrate-hydrate solid. Seventy percent of the blue shift is attributed to ground state stabilization, the rest to excited state repulsion. Spin-orbit effects are found to be small for this dimer. Homogeneous broadening is found to be slightly smaller for the dimer than for the free Cl(2). The reflection principle and spectator model approximations were tested and found to be quite satisfactory. This is promising for an eventual simulation of the condensed phase spectra.

The O(1D) + H2 (X 1Σ+, v, j) → OH(X 2Π, v′, j′) + H(2S) reaction at low collision energy: when a simple statistical description of the dynamics works

In this communication, we highlight that statistical approaches for chemical reactions describe reasonably well the low energy dynamics of the title process. Consequently, such methods prove to be valuable to compute rate constants from low to room temperatures. Results are compared with experiment and recent precise quantum wave packet calculations [J. Phys. Chem. A, 2009, 113, 5285].

An ab initio study of the Ar–NO(A Σ2+) intermolecular potential

More complete molecular dynamics simulations of NO doped Ar solid upon photoexcitation of the impurity should include effects of angular variations of Ar-NO intermolecular potential. This is the main reason for presenting in this work an ab initio study of the Ar-NO(A (2)Sigma(+)) intermolecular potential. Ab initio calculations were carried out at the level of CASSCF-MRCI, with the aug-cc-pVTZ basis sets. In order to evaluate the influence of the quadruple excitations on the topology of the potential energy surface (PES), two cases were considered, that is, with and without taking into account Davidsons correction for quadruple excitations during the calculations. An analytical representation of the PES has been obtained as a function of the Jacobi coordinates of the system. In general, the PES is repulsive, except for linear directions, where two shallow wells appear. When quadruple excitations are considered, wells are located at 4.2 A (alpha=0 degrees) and 6.08 A (alpha=180 degrees) with energies of -20 and -15 cm(-1), respectively; and when are not considered, wells are located at 6.1 A (alpha=0 degrees) and 6.8 A (alpha=180 degrees) with energies of -15 and -10 cm(-1), respectively. For distances beyond 7 A, it is observed a very low energy decay and a rapid tendency to isotropic interactions.

A new ab initio potential energy surface for studying vibrational relaxation in NO(v) + NO collisions.

A new ab initio potential energy surface for the ground state of the NO-NO system has been calculated within a reduced dimensionality model. We find an unusually large vibrational dependence of the interaction potential which explains previous spectroscopic observations. The potential can be used to model vibrational energy transfer, and here we perform quantum scattering calculations of the vibrational relaxation of NO(v). We show that the vibrational relaxation for v = 1 is 4 orders of magnitude larger than that for the related O(2)(v) + O(2) system without having to invoke nonadiabatic mechanisms as had been suggested in the past. For highly vibrationally excited states, we predict a strong dependence of the rates on the vibrational quantum number as has been observed experimentally, although there remain important quantitative differences. The importance of a chemically bound isomer on the relaxation mechanism is analyzed, and we conclude it does not play a role for the values of v considered in the experiment. Finally, the intriguing negative temperature dependence of the vibrational relaxation rate constants observed in experiments was studied using an statistical model to include the presence of many asymptotically degenerate spin-orbit states.