Experimental differential cross sections for the electron impact excitation of the a 1Deltag, b 1Sigmag+, and the 6 eV states of O2

Abstract

Absolute differential cross sections for the excitation of the 1Deltag and b 1Sigmag+ states in O2 were measured at 90 degrees, and in some cases at 30 degrees as a function of electron energy from threshold up to about 18 eV and, at 4.5 and 7.5 eV, as a function of scattering angle from 10 degrees to 135 degrees. The cross sections were obtained for the v=0, and the energy dependence also for selected higher vibrational states up to v=19. The cross sections agree, within the error bars, with earlier data as far as absolute magnitude and general appearance of the curves are concerned, but there are differences in finer details of the shape of the curves. The v=0 cross sections exhibit two broad resonance bands at about 4 eV and about 8 eV for both the a 1Deltag and b 1Sigmag+ states. The cross sections compare favourably with the recent calculations of Noble, Burke and co-workers (1992), except for a larger width of the 8 eV resonance in the experiment. A comparison with theory permits a tentative assignment of the 4 eV and 8 eV bands as X 2Pig and A 2Piu resonances. The cross sections for exciting v=2 and higher levels of the a and b states consist of one band at 6.5 eV, identical in shape to the dissociative attachment (DA) band. The energy dependence of the excitation of the (... piu3pig3) 6 eV band at 90 degrees has also been measured and is compared to the earlier experiment and theory of Teillet-Billy et al. (1988, 1989).