Quenching of Li ( 2 P) by H 2 : potential energy surfaces, conical intersection seam, and diabatic bases

Abstract

The quenching of Li 1s 2 2pY 2 P to Li 1s 2 2sY 2 S by H 2 is considered using coupled-cluster and multireference con®guration-interaction techniques. g 2v 2 A 1 Y 2 B 2 and g Iv 2 PY 2 R sections of the 1 2 A H and 2 2 A H potential energy surfaces are determined. The g 2v portion of the 1 2 A H À 2 2 A H seam of conical intersection is studied. Perhaps the most signi®cant ®nding is a surprising trifurcation of this seam into a portion with only g s symmetry and the aforementioned g 2v portion.The adiabatic-to-diabatic state transformation is considered in the vicinity of the seam of conical intersection using both perturbation theory and the dipole moment operator. The 2 B 2 section of the 2 2 A H potential energy surface exhibits an exciplex in the general vicinity of the seam of conical intersection. The 2 P section of the 2 2 A H potential energy surface possesses a global minimum lying 1X86 kcal/mol below the Li 2 P H 2 asymptote. A van der Waals-like minimum with g Iv symmetry was found on the 1 2 A H potential energy surface.

New Diabatic Potential Energy Surfaces for the Li + H2 Reaction and Time-Dependent Quantum Wave Packet Studies

“…On the other hand, the LiH 2 system has long been a subject of extensive theoretical studies in the field of molecular reaction dynamics. − For example, using the spin-coupled valence bond nonorthogonal configuration interaction method, Clarke et al computed a series of ab initio energy points for collinear geometries (Li–H–H), which were then fitted by a two-dimensional spline function through interpolation. Limited to the collinear configurations, the reaction dynamics of were studied by using both classical and quantum mechanical methods.…”

“…Essentially, this entails substituting the off-diagonal element of the matrix of the DPESs, denoted as V 12 , with its absolute value, | V 12 |. However, it is well-known that the LiH 2 system possesses a conical intersection (CI) seam in C 2 v configurations, which couples its ground (1 2 A ′) and first excited states (2 2 A ′). ,,,, In a two-state system featuring a CI seam, the off-diagonal elements of the matrix of the DPESs have to satisfy an antisymmetry constraint, which results from the geometric quantization of the derivative coupling . Additionally, the permutation of identical nuclei introduces another symmetry constraint on the off-diagonal elements.…”