Recently, Gislason and Guyon (paper I) have presented a method to distinguish the two (nearly) degenerate product electronic states in a collison-induced dissociation (CID) process such as H+2 +He →H+ +H +He. This paper uses their method to systematically examine the relationship between the product electronic state and the final velocity vector of any one of the three products. The results show that if, for example, the velocity of H+ is determined, there is a range of fast H+ velocities where the products must be in the excited electronic state, a range of slow H+ velocities where the products must be in the ground electronic state, and an intermediate range of H+ velocities where the final electronic state is not uniquely determined. Analogous results are derived for the measurement of either the H or He final velocity. An example of this behavior is shown from our trajectory–surface-hopping study of CID in the H+2 +He system. In addition, several previous CID experiments are reconsidered here in light of the present considerations.
The effect of surface crossings on ion-molecule reactions is investigated. A model is proposed to locate these crossings and determine their effect on reactive cross sections. The model successfully explains why some ion-molecule reactions have cross sections larger than the Langevin value. It also explains why the two spin-orbit states of Ar+ have different cross sections for reaction with H2.
We have determined velocity vector distributions for NO+ and O2+ scattered from helium. As expected, the small angle scattering is elastic, but at angles greater than 60°, inelasticity which increases with the scattering angle is apparent. For angles greater than 100°, this inelasticity represents vibrational excitation of the molecule–ion. For initial relative kinetic energies between 4.3 and 25 eV and 180° scattering, the variation of the inelasticity is consistent with a new, corrected version of the classical theory of vibrational excitation. Three methods of calculating the angular variation of the inelasticity are presented and found to be consistent with the experimental data.
Product-velocity-vector distributions have been determined for the reactive and inelastic scattering of N2+ by H2, D2, and HD. These distributions show that the reaction proceeds by a direct short-lived interaction rather than by a long-lived collision complex. Most products are scattered in the original direction of the N2+ projectile at a speed somewhat greater than calculated from the ideal stripping model. The internal excitation of N2D+ and N2H+ is very high and decreases somewhat with increasing scattering angle. For HD there is an isotope effect that favors N2H+ by large factors at small scattering angles, and N2D+ by smaller factors at large angles. The N2+ scattered from D2 shows very little elastic component, but does reveal an inelastic process which is probably the collisional dissociation of D2.
Starting with the fundamental and general criterion for a spontaneous process in thermodynamics, ΔStot ≥ 0, we review its relationships to other criteria, such as ΔA and ΔG, that have limitations. The details of these limitations, which can be easily overlooked, are carefully explicated. We also bring in the important example of electrical energy to show how criteria for spontaneity are properly applied to electrochemical cells. The analysis in this article gains clarity from use of the "global" formulation of thermodynamics and from carrying out finite changes of thermodynamic properties rather than manipulating differential changes. Several examples are given.
