Dissociation of vibronic states of C–1A′ DCN: Quantum treatment

Abstract

The rates of dissociation of several vibrational states of nπ* excited (C–1A′) DCN have been determined via quantum dynamical means in which only the CD stretching and DCN bending motions are treated. The ab initio configuration interaction potential energy surface used in our earlier classical trajectory study of these same dissociation rates was employed in the present study. The results of this quantal study tend to support our earlier prediction that v2→v1 (bending-to-stretching) energy transfer plays an important role in determining the dissociation rates of these vibronic states. Surprisingly, the absolute rates obtained via the quantum method are in quite close agreement with a certain component of the classically determined rates.

Semiclassical vibrational wave functions for electronically excited DCN: A highly quantum mechanical system

“…IV A. 5. Trajectory (f) is the only one shown here which contains less than zeropoint energy (specifically in the stretching mode).…”

“…II A, hence gn(X, y) = L ak¢JJx, y)e-iEkln/h. (5) k At tn = 0, the phase factor is unity. The spatial overlap of the initial (tn = 0) es function with subsequent es functions results in an overlap which is a function only of time; this entity is often referred to as an autocorrelation function:…”

“…The state labels: v I, V2 represent the quanta of excitation in the stretching and bending modes, respectively. In (e') the state labeled [5,0] represents the quantum number assignment of the resonance-zone state (see Appendix). The state assignments of these energies are discussed in Secs.…”

“…1), V(r, fJ), is not simply a model function; it is a least-squares polynomial fit of nearly 100 ab initio configuration interaction (CI)-level energies appropriate to a variety of molecular geometries (with the C-N bond length held fixed at the equilibrium value for this electronic state).3 Therefore, the resulting two-dimensional surface is designed to provide a good approximation to reality for the D-CN stretching and bending motions of the excited DCN molecule. This surface poses a unique opportunity to test the SQ method on a nonmodel potential for which both classical trajectorl and quantum mechanical calculations 5 have already been performed and analyzed relative to the excellent experimental data 6 which exists on the dynamics of this electronic state ofDCN. The contrast between this potential surface and many of the model potentials which are typically utilized in semiclassical calculations should be stressed.…”

“…The semiclassical vibrational wave functions generated for DCN in this study are compared to the corresponding quantum mechanical eigenfunctions determined previously using a basis-set expansion method described in Ref. 5. In that earlier work, the same ab initio CI electronic energies were least squares fit to a functional form which was especially convenient for use in the quantum analysis, and the bound state wave functions were determined from the Hamiltonian eigenvectors whose eigenenergies were below the D + CN* dissociation threshold appropriate to this C state of DCN.…”