An optimal adiabatic-to-diabatic transformation of the 1 2A[prime] and 2 2A[prime] states of H3

Molecular reaction dynamics in the adiabatic representation is complicated by the existence of conical intersections and the associated geometric phase effect. The first-derivative coupling vector between the corresponding electronically adiabatic states can, in general, be decomposed into longitudinal (removable) and transverse (nonremovable) parts. At intersection geometries, the longitudinal part is singular, whereas the transverse part is not. In a two-electronic-state Born–Huang expansion, an adiabatic-to-diabatic transformation completely eliminates the contribution of the longitudinal part to the nuclear motion Schrödinger equation, leaving however the transverse part contribution. We report here the results of an accurate calculation of this transverse part for the 1 2A[prime] and 2 2A[prime] electronic states of H3 obtained by solving a three-dimensional Poisson equation over the entire domain [sans-serif U] of internal nuclear configuration space [script Q] of importance to reactive scattering. In addition to requiring a knowledge of the first-derivative coupling vector everywhere in [sans-serif U], the solution depends on an arbitrary choice of boundary conditions. These have been picked so as to minimize the average value over [sans-serif U] of the magnitude of the transverse part, resulting in an optimal diabatization angle. The dynamical importance of the transverse term in the diabatic nuclear motion Schrödinger equation is discussed on the basis of its magnitude not only in the vicinity of the conical intersection, but also over all of the energetically accessible regions of the full [sans-serif U] domain. We also present and discuss the diabatic potential energy surfaces obtained by this optimal diabatization procedure

Geometric phase effects in H3 predissociation

We model the predissociation of H3 in the electronic state corresponding to the upper sheet of the conically intersecting 1 2A[prime] and 2 2A[prime] states, and we show that product-state rovibrational distributions are strongly influenced by the geometric phase. Similarly, the differences in the product-state energy distributions in recent three-body dissociation experiments for the 2s,2A1[prime] and 2p,2A2[double-prime] states of H3 are shown to result from the presence of the geometric phase in this system, and thus provide experimental evidence of the influence of this phase in a molecular dynamical process

A quantum and semiclassical study of dynamical resonances in the C + NO-->CN + O reaction

Accurate quantum mechanical reactive scattering calculations were performed for the collinear C+NO-->CN+O reaction using a polynomial-modified London Eyring Polanyi Sato (PQLEPS) potential energy surface (PES), which has a 4.26 eV deep well in the strong interaction region, and a reference LEPS PES, which has no well in that region. The reaction probabilities obtained for both PESs show signatures for resonances. These resonances were characterized by calculating the eigenvalues and eigenvectors of the collision lifetime matrix as a function of energy. Many resonances were found for scattering on both PESs, indicating that the potential well in the PQLEPS PES does not play the sole role in producing resonances in this relatively heavy atom system and that Feshbach processes occur for both PESs. However, the well in the PQLEPS PES is responsible for the differences in the energies, lifetimes, and compositions of the corresponding resonance states. These resonances are also interpreted in terms of simple periodic orbits supported by both PESs (using the WKB formalism), to further illustrate the role played by that potential well on the dynamics of this reaction. The existence of the resonances is associated with the dynamics of the long-lived CNO complex, which is much different than that of systems having an activation barrier. Although these results were obtained for a collinear model of the reaction, its collinearly-dominated nature suggests that related resonant behavior may occur in the real world