Inelastic low-energy electron collisions with the HBr and DBr molecules: Experiment and theory - art. no. 062710

Low-energy electron collisions with the HBr and DBr molecules are addressed from the experimental and theoretical points of view. Relative differentia l cross sections for the excitation of vibrational levels of HBr and DBr up to upsilon = 6 have been measured as a function of the incident electron e nergy in the range 0-4 eV. In addition to the shape resonance near 2 eV col lision energy, intense and narrow threshold peaks are found for the excitat ion of the upsilon = 1 level of HBr and the upsilon = 1 and upsilon = 2 lev els of DBr. Measurements with high resolution for rotationally cooled molec ules have revealed the existence of sharp oscillatory structures in the ela stic and upsilon = 0 -->1 cross sections in a narrow range below the dissoc iative-attachment threshold. The dissociative-attachment cross section has been measured with high resolution of the incident electrons in the range 0 .2-1.4 eV. The theoretical analysis is based on an improved nonlocal resona nce model, which has been constructed on the basis of existing fixed-nuclei electron-HBr scattering phase shifts and accurate ab initio calculations o f the bound part of the HBr- potential-energy function. This purely ab init io-based model is used to calculate integral electron-scattering and dissoc iative-attachment cross sections for HBr and DBr. The theoretical cross sec tions agree very well with the experimental data. The observed threshold pe aks and Wigner cusp structures in the vibrational excitation functions are correctly reproduced. The sharp structures in the upsilon = 0 -->0 and upsi lon = 0 -->1 cross sections below the dissociative-attachment threshold, co nsisting of a superposition of boomerang-type oscillations and quasibound l evels of the outer well of the HBr- potential-energy function, are quantita tively described by the theory. The high degree of agreement between experi ment and theory indicates that the essentials of low-energy electron-HBr co llision dynamics are completely understood.