Variable angle electron-impact excitation of nitromethane

The electron-impact excitation of nitromethane has been studied at incident electron energies of 25, 55, and 90 eV, at scattering angles from 60 to 800. The lowest-lying inelastic process which is observed is a previously unreported feature with a maximum intensity at 3.8 eV energy loss. This feature represents at least one singlet→triplet transition. It is likely that this 3.8 eV triplet feature plays a central role in the gas phase photolysis of nitromethane. A weak inelastic process with a peak at 4.45 eV has also been observed, as has a strong transition at 6.23 eV. Both of these excitations are well known from optical spectra, and they are generally believed to represent spin-allowed n→π* and π→π* transitions, respectively. Their assignments are discussed in detail. In addition, seven other transitions, several of which have not been reported previously, have been detected in the 7--12 eV energy-loss range. Three of these transitions, at 8.3, 8.85, and 11.73 eV energy loss, are tentatively assigned to Rydberg excitations of increasingly tightly bound electrons into a 3s Rydberg orbital