15min:
BOUND RO-VIBRATIONAL STATES OF H2...CN(X2 Sigma +) VAN DER WAALS COMPLEX.

ALEXEY L. KALEDIN, MICHAEL C. HEAVEN, JOEL M. BOWMAN, Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322.

~The abstraction reaction H2+CN longrightarrow H+HCN proceeds via a collinear transition state. The entrance channel to this transition state may be examined through spectroscopic studies of the H2-CN van der Waals complex. In addition, as the barrier to reaction is only 1200 cm-1, it may be possible to initiate reaction within the cluster by vibrational excitation of the H2 moiety. To learn more about the pre-reaction dynamics and identify states that sample the transition state geometry, we have examined the characteristics of bound states supported by the van der Waals well.

~A previously reported 4-D interaction potential (with H2 and CN bonds fixed) was used to calculate the bound states for J=0,1,..., ignoring spin. The ro-vibrational eigenstates are calculated in a body-fixed formalism, where the unsigned projection of J onto van der Waals bond ( K ) and its reflectional parity ( epsilon) are nearly good quantum numbers. For the para -H2 complex the lowest energy state is K =0+ corresponding to the J=0 manifold. Its binding energy with respect to the H2(j=0)+CN(j=0) asymptote is \verb@~@16 cm-1. Similarly, the ortho -H2 complex has a K =0+ ground state deriving from J=0. It is bound by \verb@~@31 cm-1 relative to the H2(j=1)+CN(j=0) asymptote. In both cases, the first excited state is only \verb@~@1 cm-1 above the zero point; it derives from J=1 and belongs to K =0- symmetry with some mixing from K =1- state. Potential and Coriolis coupling terms mix different K and epsilon states, rendering the eigenstate structure very complicated. Examination of probability density for the ortho -H2 complex showed that some low-lying states sample the linear H-H...C-N geometry.