Cross-sections exhibiting quantum resonances: the B+OH case

Extensive theoretical quantum-mechanical calculations are reported for the cross-section and related dynamical quantities of the B + OH --> BO + H rea ction, on a previously developed potential-energy surface (PES) describing the ground electronic state. These calculations show, as an outstanding fea ture, the presence of marked structures in the shape of the excitation func tion as a consequence of the existence of a dense spectrum of rather long-l ived resonance states. These are narrow enough to survive the angular momen tum averaging, thanks to an important stabilization caused by an electronic minimum corresponding to a linear HOB configuration. The centrifugal barri ers due to high values of the orbital angular momentum are found to lead to several orbiting shape resonances, as revealed by the opacity function plo ts and the dependence of the reaction probability on energy. Differential c ross-sections corresponding to energies lying at either reactivity peaks or valleys in the integral cross-section show a highly symmetric dependence o n scattering angle, indicating an important resonant contribution to reacti vity in both cases. The possibility of directly observing resonances in exp erimental integral cross-section measurements is analysed in the light of t he present results. (C) 1999 Published by Elsevier Science B.V. All rights reserved.