Observation of temporary-negative-ion states in condensed methanol via vibrational excitation induced by slow electron scattering

We report the measurements of electron-impact vibrational excitation of amorphous methanol condensed on a polycrystalline Pt substrate over incident energies of 1{endash}20 eV at a large off-specular angle. The spectra obtained show that vibrations within solid methanol in its ground state are rather sensitive to the variation of impact energy and there is tangible evidence of the formation of at least three compound temporary-negative-ion (TNI) states. The low-energy feature lying between 3 and 6 eV is assigned tentatively to a {sup 2}{ital A}{prime} valence-shape resonance with a {sup 2}[{ital N},(8{ital a}{prime}{sigma}{asterisk}){sup 1}] configuration, whose parent state is the ground state {sup 1}{ital A}{prime} of the molecule. The origin of the second broad structure centered around 7.0 eV in the excitation functions may be threefold: a Feshbach-type resonance {sup 2}{ital A}{double_prime} of the electronic configuration {sup 2}[(2{ital a}{double_prime}){sup 1},(3{ital sa}{prime}){sup 2}] (about 7 eV); a nearby shape resonance {sup 2}{ital A}{prime} of {sup 2}[({ital N}),(9{ital a}{prime}{sigma}{asterisk}){sup 1}] (about 8 eV); and probably also a minor contribution from another {sup 2}[(7{ital a}{prime}){sup 1},(3{ital sa}{prime}){sup 2}] Feshbach resonance {sup 2}{ital A}{prime} (about 9 eV). The third broad bandlike resonant feature, extending from 11 up to 17 eV, may consist of overlapping TNI states, dominated by the {sup 2}[(6{ital a}{prime}){sup 1},(3{ital sa}{prime}){sup 2}] Feshbach resonance {sup 2}{ital A}{prime}. Plausible decay channels from their configurations are discussed. {copyright} {ital 1996 The American Physical Society.}