CLASSICAL TRAJECTORY CALCULATIONS ON GAS-PHASE REACTIVE COLLISIONS

The recent (since 1983) literature on classical trajectory calculations on gas phase reactions is reviewed. It is seen that this continues to be a vigorous area of research, yielding considerable insight into the microscopic details of reaction mechanisms, as well as being a relatively simple means of calculating cross-sections and rate constants. The necessary theoretical background is touched upon briefly, and several caveats are pointed out. A few model reactions continue to be the subject of intensive activity, most notably the reactions H + H2 --> H2 + H and F + H2 --> FH + H, the prototypical thermoneutral and exoergic systems respectively. These reactions are unusual in that their potential energy surfaces are relatively well known. For this reason, among others, comparisons of quantum and classical dynamics on these systems are common. Recent advances in quantum mechanical scattering theory have greatly increased the feasibility of exact calculations for the transfer of H atoms between heavier atoms. Spurred by this development, the number of classical treatments of light-atom transfer has increased dramatically. This work is considered here in some detail. Largely due to recent breakthroughs in experimental technique, there has been a renewal of interest in the influence of reactant vibration and rotation on reactivity. Many trajectory studies reflect this interest. Other topics include the treatment of reactions dominated by long-range attraction, in which the traditional Langevin approach has often been found wanting, non-adiabatic reactions, and collision-induced dissociation. Finally, the one area in which the classical trajectory technique is still the only viable technique is in the treatment of polyatomic molecules. Recent calculations are summarized.