The details of inelastic energy transfer between a diatomic, classical, harmonic oscillator, A—B, and a hard-sphere atom C are explored for the simple case of colinear collisions. The influence of the masses MA, MB, and MC on the efficiency of energy transfer is examined in detail. The case of equally matched masses (MB = MC) does not necessarily correspond to high efficiency. It is shown that for colinear collisions not all phase angles of the oscillator can occur at the instant of collision, but that instead certain phase angles are excluded. In the case of a highly excited oscillator in a ``cold'' gas, these excluded phase angles are just those that restrict the energy transfer from the oscillator to small amounts of energy. For a harmonic oscillator, near the dissociation threshold, this implies a small, stepwise deactivation process. It is also shown that even for the hard-sphere case, 100% efficiency of energy transfer is not possible, i.e., there is an activation energy in excess of the energy transferred. This is required as an ``escape energy'' in order to avoid a double collision whose effect would be to reduce the energy transferred. This escape phenomenon is also shown kinetically to favor stepwise energy transfer for quantized oscillators. Some simple cases of rotational-energy transfer are examined.

Articles you may be interested inVibrational energy transfer from highly excited anharmonic oscillators: Quasiclassical Monte Carlo trajectory study of Br2-Ar and Br2-Br system J. Chem. Phys. 82, 4903 (1985); 10.1063/1.448662Vibrational energy transfer from highly excited anharmonic oscillators. Dependence on quantum state and interaction potentialThe probabilities of dissociation P dis, excitation P ex, de-excitation P de, and the associated average energy exchanges were calculated theoretically for a highly energized, anharmonic oscillator (12 or Brz) colliding classically with an inert gas atom C through a Morse-type potential. The effect of varying mass and well depth was investigated.It was found that the effect of anharmonicity is to favor excitation and dissociation. However, the average dE. for these processes is about the same for harmonic and anharmonic oscillators and not much bigger than 1 to 2 RT. P dis increases markedly with increasing mass. The well depth (Vo) does not seem to have much effect in the range 0.004< Vo/Do<0.14, where Do is the bond dissociation energy. Exchange reactions are observed, but for shallow well depths they are rare events. From the results, it is possible to calculate A, the probability of stabilizing an atom pair by a third-body collision. This turns out to be independent of temperature but depends strongly on the mass of the third body C. It is always in the range 0.1

The effects of reaction barrier height and initial rotational excitation of the reactants on the overall rate of H atom exchange between atomic chlorine and HCl ( v = 0) and on the 0 -+ 1 vibrational excitation of HCI via reactive and nonreactive collisions have been investigated using quasiclassical trajectory techniques. Two empirical LEPS potential energy surfaces were employed in the calculations having reaction barrier heights of 9.84 and 7 05 kcal mol-'. Trajectory studies of planar collisions were carried out on each surfacc over a range of relative translational energies with the ground-state HCl collision partner given initial rotational excitation corresponding J = 0 , 3 , and 7. Initial molecular rotation was found to be relatively inefficient in promoting the H atom exchange; the computed rate coefficient for H atom exchange between C1 + HCl (ZI = 0, J = 7) was only 4 times larger than that for C1 + HCl (ZI = 0, J = 0). The vibrational excitation rate coefficient exhibited a stronger dependence on initial molecular rotational excitation. The observed increase in the vibrational excitation rate coefficient with increasing initial molecular rotational excitation was due primarily to nonreactive intermolecular R + V energy transfer. The vibrational excitation rate coefficients increase with decreasing reaction barrier height.

The classical equations of motion of colliding diatomic molecules are solved rigorously in two dimensions to obtain the energy transferred to the internal degrees of freedom during collision. The model considers up to four atoms bound by six atom-centered Morse potentials. The effect of varying range parameters is noted. The relaxation of H2 with He and H2 collision partners, D2 with He, and pure N2 and O2 is studied. The vibration—rotation energy exchange is evaluated and accounted for. The resulting relaxation times and average collision numbers agree well with empirical findings. In the temperature range 100°—700°K, except for N2 and O2, a negative temperature dependence was obtained. The contrary is expected at higher temperatures where the relaxation times are functions of the inverse collision frequency only.

The change of energy of a diatomic molecule upon collision with an atom in two dimensions was calculated. The energy contributed to the various internal degrees of freedom of the molecule was evaluated. The vibrational transition probabilities obtained were compared to experimental data for the case of O2→Ar collisions. By contrasting these results with those of a one-dimensional treatment, the form of a realistic three-dimensional potential function was predicted. It was found that at lower initial rotational energies, transfer of energy from rotational to vibrational degrees of freedom is as effective as translational→vibrational transfer. For higher initial rotational energy, rotational→vibrational transfer is shown to be less probable.