BOUND RO-VIBRATIONAL STATES OF $H_{2}\ldots CN(X^{2}\Sigma^{+})$ VANDER WAALS COMPLEX
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Date
1999
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Ohio State University
Abstract
The abstraction reaction $H_{2}+CN \to H+HCN$ proceeds via a collinear transition state. The entrance channel to this transition state may be examined through spectroscopic studies of the $H_{2}-CN$ 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 $H_{2}$ 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 $H_{2}$ and CN bonds fixed) was used to calculate the bound states for $J=0,1,\ldots$, 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 (c) are nearly good quantum numbers. For the $para-H_{2}$ complex the lowest energy state is $K=0^{-}$ corresponding to the $J=O$ manifold. Its binding energy with respect to the $H_{2}(j=0)+CN(j=0)$ asymptote is $^{-16}cm^{-1}$. Similarly, the $ortho-H_{2}$ complex has a $K=0^{+}$ ground state deriving from $J=0$. It is bound by $^{-}31 cm^{-1}$ relative to the $H_{2}(j=1)+CN(j=0)$ asymptote. In both cases, the first excited state is only $^{-}1 cm^{-1}$ 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 c states, rendering the eigenstate structure very complicated. Examination of probability density for the $ortho-H_{2}$ complex showed that some low-lying states sample the linear $H-H\ldots C-N$ geometry.
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Author Institution: Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University