The unimolecular dissociation of HCO: I. Oscillations of pure CO stretching resonance widths

Abstract

The unimolecular dissociation of the formyl radical HCO in the electronic ground state is investigated using a completely new ab initio potential energy surface. The dynamics calculations are performed in the time-independent picture by employing a variant of the log-derivative Kohn variational principle. The full resonance spectrum up to energies more than 2 eV above the vibrational ground state is explored. The three fundamental frequencies (in cm−1) for the H–CO and CO stretches, and the bending mode are 2446 (2435), 1844 (1868), and 1081 (1087), where the numbers in parentheses are the measured values of Sappey and Crosley obtained from dispersed fluorescence excitation spectra [J. Chem. Phys. 93, 7601 (1990)]. In the present work we primarily emphasize the dissociation of the pure CO stretching resonances (0v20) and their decay mechanisms. The excitation energies, dissociation rates, and final vibrational–rotational state distributions of CO agree well with recent experimental data obtained from stimulated emission pumping. Similarities with and differences from previous time-independent and time-dependent calculations employing the widely used Bowman–Bittman–Harding potential energy surface are also discussed. Most intriguing are the pronounced oscillations of the dissociation rates for vibrational states v2≥7 which are discussed in the framework of internal vibrational energy redistribution.