Dissociative double ionization of CO₂: dynamics, energy levels and lifetime

Abstract

In a kinematically complete experiment on the dissociative double ionization of CO₂ by electron impact, spontaneous and metastable decay have been observed via the channel C O₂²⁺→CO⁺+O⁺. The metastable decay shows a lifetime of 5.8±1.5 μs. The measured kinetic energy release spectrum of the dissociation shows one broad peak. To understand the observed features, ab initio potential energy surface (PES) for the ground electronic state of C O₂²⁺ was computed using a multireference configuration interaction method and a correlation-consistent polarized-valence quadruple-ζ basis set, for a range of internuclear distances and O-C-O bond angles, and an analytic fit of the PES was obtained. The computed PES clearly indicates the metastability of the dication and yields a barrier height and an asymptotic limit in fair agreement with the reported data. A time-dependent quantum mechanical approach was used to compute the ground vibrational state wave function of CO₂ in its ground electronic state. Assuming a Franck-Condon transition, the same function was taken to be the initial wave function at time t=0 for the time evolution on the fitted PES for the ground electronic state of C O₂²⁺. The autocorrelation function was computed and Fourier transformed to obtain the excitation spectrum. Upon convolution with the instrument resolution function, the kinetic energy release spectrum was obtained, in good agreement with the experimental results, particularly at lower energies. The discrepancies at higher energies are attributed to the noninclusion of the excited states of C O₂²⁺ in the dynamical study.