Calculating Feshbach resonances in HCO using an extension of Qim‐path theory

Abstract

AbstractWe present a theoretical study of Feshbach resonances in HCO, using an extension of a previous projection theory [Y. Wang and J. M. Bowman, J. Chem. Phys. 139, 154303 (2013)] that makes use of projections of the normal modes of HCO onto a one‐dimensional rectilinear path along the imaginary‐frequency normal mode of the dissociation saddle point. HCO dissociation is strongly mode specific, because the CH‐stretch is nearly coincident with this path. The projection theory predicts that HCO dissociates with a subpicosecond lifetime for the CH‐stretch excited to the second overtone ( ), in agreement with rigorous calculations done 20 years ago. However, the CO‐stretch and HCO bend have small projections on the path and so no dissociation is predicted from the simple theory, even for highly excited states. By making an extension of the projection theory to describe coupling of these modes to the CH‐stretch, dissociation rates can be obtained for these modes. Semi‐quantitative results are obtained using vibrational self‐consistent field/virtual‐state configuration interaction calculations with the code MULTIMODE. The dissociation lifetimes for many states involving excitation of these modes are compared with previous rigorous calculations and experiment and encouraging agreement is found.