I. Oref

Minimal separation distance in energy transferring collisions. Trajectory calculations

Abstract Classical trajectory calculations of toluene-Ar collisions were performed. The energy transferred in up, down and all collisions is reported as a function of the minimal distance, MD, of approach between the Ar atom and the nearest atom to it in the toluene molecule. There is a distribution of MD at which energy transfer takes place and most energy transfer occurs in the range 0.29–0.35 nm. Increasing the temperature shifts the average to lower values. The collision duration and the MD are independent. The average MD is 0.308 nm at 300 K and 0.299 nm at 1500 K. Supercollisions were found but no correlation could be made between their duration and their MD.

Dynamics and energy release in benzene/Ar cluster dissociation

Energy disposal distributions and cluster lifetimes of Ar–benzene clusters (ABC) were studied by quasiclassical trajectory calculations. Four intermolecular potentials, Lennard-Jones, ab initio, and two Buckingham-type potentials, were used in the calculations. The Ar atom was placed in one of the five minima of the potential surface at 0 K. The benzene monomer in ABC at 0 K was excited to various internal energies, and internal energy loss of the monomer following dissociation was calculated. The average energy removed, 〈ΔE〉, depends on the well depth of the potential and on the initial structure of the cluster. The highest value was obtained when the cluster was formed at the deepest well, in which the Ar atom is above the center of the ring. Regardless of the initial structure, it was found that the atom migrated from well to well including the deepest, and dissociation occurred from a structure different from the initial one. No correlation was found between the energy removed and the cluster lifetime...

Laser-induced two-photon decomposition of azoethane

Abstract Azoethane undergoes two-photon photodissociation when irradiated by a Q-switched ruby laser. The two-photon nature of the process is demonstrated quantitatively for the first time in a gas-phase reaction. The absorption cross section is found to be δ = (6.5 ± 2.5) × 10−52 cm4 sec/photon molecule.

Energy release in benzene–argon cluster dissociation – quasiclassical trajectory calculations

Abstract Results of quasiclassical trajectory calculations of the dissociation of a highly excited argon–benzene van der Waals cluster are reported. Two intermolecular potentials were used. The average energy removed from the excited benzene molecule, 〈ΔE〉, is −886 cm−1 for Lennard-Jones potential and −436 cm−1 for ab initio potential. The average trajectory lifetimes are 36.3 and 80.4 ps, respectively. The ΔE distribution shows a supercollision tail. No correlation was found between the lifetime of the cluster and the value of ΔE. The effects of the nature of the potential on the values of 〈ΔE〉 and on the long lifetime of the cluster are discussed.

Termolecular collisions between benzene and Ar

Termolecular collisions between a benzene molecule and two Ar atoms were studied by quasiclassical trajectory calculations. The calculations show that termolecular collisions form termolecular complexes and occur by three mechanisms: (a) the Chaperon mechanism, in which the first Ar in is the first Ar out of the termolecular complex, is the dominant one at high pressures. Two-thirds of all termolecular collisions go by this mechanism. (b) The energy transfer mechanism, in which the first Ar in is the last Ar out of the termolecular complex, comprises about a quarter of all termolecular collisions at high pressures. (c) The concerted channel, in which both argon atoms depart from the benzene simultaneously and does not lead to products in reactive systems, comprises about 10% of all termolecular collisions. Energy transfer quantities and collision complex lifetimes in binary and termolecular collisions are evaluated and their dependence on inter- and intramolecular harmonic and anharmonic potentials, tempe...

Singlet-triplet absorption spectra of azoalkanes

Abstract The singlet-triplet absorption spectra of trans -azo-methane, trans -azo-ethane, trans -azo- n -propane, and trans -azo- iso -propane have been measured using the technique of oxygen perturbation. It was found that the triplet level lies 55.5 ± 1.5 kcal mole −1 above the ground state in these compounds. These results are compared with other measurements of the triplet energies of acyclic azo-compounds and the relevance of this energy to their photochemistry is discussed.

INTRAMOLECULAR ENERGY REDISTRIBUTION IN C60 FOLLOWING HIGH-ENERGY COLLISIONS WITH LI+

Abstract Quasiclassical trajectory calculations are used to investigate the dynamics of intramolecular energy redistribution, IVR, following a sudden excitation of a C 60 molecule by a high-energy Li + ion. During the collisions, ∼6 and ∼14 eV of translational energy were transferred to the C 60 and converted to internal energy. Only four normal modes, identified by fast Fourier transforms, out of the available 174 modes, were excited and participated in the initial phase of IVR. It took 60 fs for the excitation to move from the front to the back of the molecule. Total relaxation was obtained, however, only after few ps.

Anharmonicity effects in cluster isomerization

Abstract The dynamics of Na 4 Cl 4 clusters is explored and various methods of calculating cluster reaction rates are compared. The Na 4 Cl 4 cluster undergoes isomerization from a low temperature cube to ladder and ring forms. The potential surface is dotted with low barriers such that back and forth reactions take place and at equilibrium significant concentrations of the ladder and the ring forms are present. Molecular dynamics and statistical methods of calculating rate coefficients are compared and the effects of internal energies and anharmonicities on the rate coefficients are discussed. The effects of a non-steady state between an activated molecule and a transition state on the energy-dependent RRKM rate coefficient are evaluated.