Beatriz Miguel

Hybrid quantum/classical simulation and kinetic study of the vibrational predissociation of Cl2⋯Nen (n=2, 3)

A hybrid quantum/classical method is applied to the vibrational predissociation of van der Waals clusters containing a diatomic molecule and several rare gas atoms, Cl2⋯Nen (n=2, 3). The vibrational degree of freedom of the diatomic is treated quantum mechanically while all the other degrees of freedom are treated classically. A kinetic mechanism is proposed in order to interpret the dynamics in terms of the following elementary steps; vibrational predissociation (VP), intramolecular vibrational redistribution (IVR), and evaporative cooling (EC). The resulting lifetimes are in very good agreement with the experimental linewidth measurements of Janda and co-workers, and with the quantum mechanical reduced-dimension results of Le Quere and Gray on Cl2⋯Ne2. The final rotational state distributions agree very well with the experimental results and exhibit a quasistatistical behavior. The final vibrational distributions reproduce the main experimental features.

Molecular dynamics simulation of the I2(X)⋯Ar isomers population in a free-jet expansion: Thermodynamics versus kinetic control

A molecular dynamics simulation addressing the problem of thermodynamic versus kinetic control of the isomers population of van der Waals complexes in a supersonic expansion is presented. The populations of the linear and T-shaped isomers of I2(X)⋯Ar in a supersonic beam expansion were determined by molecular dynamics simulation as a function of the distance to the nozzle and compared to the prediction of thermodynamics. The surprising conclusion is that although there is a barrier equal to half the well depth between the two isomers, their populations are consistent with the existence of thermodynamic equilibrium. This result is rationalized by examining the cooling mechanisms in the Ar+I2(X)⋯Ar collisions. In addition to the direct isomerization, a new mechanism (swap cooling), which induces isomerization even for complexes with barriers above the dissociation limit, is evidenced.

Time evolution of reactants, intermediates, and products in the vibrational predissociation of Br2⋯Ne: A theoretical study

A hybrid quantum/classical simulation of the vibrational predissociation of the Br2⋯Ne cluster in the B state is carried out. The resulting lifetimes and final rovibrational state distributions compare very well with the experimental measurements, as well as with accurate quantum mechanical results. The time-evolution of the reactants, products, and intermediates is analyzed by a kinetic mechanism, comporting three elementary steps: direct vibrational predissociation (VP), intramolecular vibrational redistribution (IVR), and evaporative cooling (EC). The importance of intramolecular vibrational redistribution followed by evaporative cooling relative to direct vibrational predissociation is shown to evolve from 100% of VP for the lowest initial vibrational level v=10 to 53% for the highest one v=27. In the cases where IVR is important, the complexes are shown to explore the whole configuration space, in contrast with the cases where dynamics are governed by direct vibrational predissociation for which the ...

Surface hopping simulation of the vibrational relaxation of I2 in liquid xenon using the collective probabilities algorithm

A surface hopping simulation of the vibrational relaxation of highly excited I(2) in liquid xenon is presented. The simulation is performed by using the collective probabilities algorithm which assures the coincidence of the classical and quantum populations. The agreement between the surface hopping simulation results and the experimental measurements for the vibrational energy decay curves at different solvent densities and temperatures is shown to be good. The overlap of the decay curves when the time axis is linearly scaled is explained in terms of the perturbative theory for the rate constants. The contribution of each solvent atom to the change of the quantum populations of the solute molecule is used to analyze the mechanism of the relaxation process

Size evolution of the vibrational predissociation process in Br2...Nen clusters: simulation and kinetic study.

A hybrid quantum-classical simulation of the vibrational predissociation of Br2...Nen, (n = 2-11) clusters in the B electronic state is carried out. The time-evolution of the reactants, products, and intermediates is analyzed by a kinetic mechanism consisting of three elementary steps: direct vibrational predissociation (VP), intramolecular vibrational redistribution (IVR), and evaporative cooling (EC). The importance of intramolecular vibrational redistribution followed by evaporative cooling relative to direct vibrational predissociation is shown to increase rapidly with increasing cluster size. Final product state distributions reveal that only one or less Br2 stretching quantum per neon atom is required in order to achieve complete dissociation (n quanta for n < or = 9 and n - 1 for n = 10 and 11). The proportion of available energy going into translation is proposed as a parameter to study the statistical behavior of the Van der Waals clusters. It is shown to depend only on the number of remaining degrees of freedom, a characteristic of a statistical behavior, for n > or = 3.

Single-exponent Slater function expansions for lithium to neon atoms

Single-exponent Slater function (SESF) expansions which reduce the computation time of integrals in the calculation of the electronic structure are presented for lithium to neon atoms. The exponents of the SESF were determined by minimizing the total energy and the virial ratio error at the Hartree - Fock level. Several test applications of the new sets are presented: calculations of ground states of Li to Ne atoms including the correlation energy and preliminary results for diatomic molecules with the integral package adapted to the MRDCI program.

Erratum: “Time evolution of reactants, intermediates and products in the vibrational predissociation of Br2⋅⋅⋅Ne: A theoretical study” [J. Chem. Phys. 113, 10130 (2000)]

The lower part of Fig. 6 was erroneous, due to a transcription error. The MDQT and experimental results now show a much better agreement with the quantum mechanical ones for the Δv=−2 channel of the Br2⋅⋅⋅Ne(v=27) vibrational predissociation, as was the case for the other channels and the other initial vibrational levels. The rest of the paper is unchanged.