Production of the excited hydrogen atom (n = 4) by controlled electron impact on methanol

Dissociation of methanol for the formation of the excited hydrogen atom (n = 4) from the methyl and the hydroxyl groups has been investigated by precise measurements of the shapes and intensities of the Balmer β line. The translational energies of H* and D* are 1.4-3.1 eV, indicating no isotope effect. Their threshold energies are 18.2-18.5 eV, indicating no significant difference for both groups. The relative scission probabilities of the C-H and O-H bonds and the isotope effect in bond dissociation depend on electron energies: C-H/C-D = 0.70-0.91, 0-D/O-H = 0.41-0.59, C-D/O-D = 0.69-1.08, and C-H/O-H = 0.55. These results and an analysis based on a quasi-equilibrium theory suggest that the vibrationally excited Rydberg states converging to the (sigma/sub OH/)-1 ionized state are important intermediates for the formation of the excited hydrogen atom near the threshold energy