Studies of the electron-impact ionization cross section of vibrationally excited oxygen employing a shock-heated molecular beam.

Abstract

The shock-heated molecular-beam technique was used to obtain vibrationally excited oxygen molecules. The vibrational distributions of these diatomic molecules, in argon gas as the ``carrier'' gas of a shock-heated molecular beam, have been calculated by considering atomic recombination, collisional excitation, and deexcitation during the expansion. The vibrationally excited molecules, which correspond to vibrational temperatures ${T}_{v}$, in the range 1800--7000 K, are used to examine the role played by vibrational excitation in both direct and dissociative electron-impact ionization cross sections over a range of electron energies from 50 to 500 eV. The results show that the dissociative electron-impact ionization cross section increases only slightly with increasing vibrational temperatures, and results agree with the theory based on the modified reflection method.