Electron impact excitation of the gamma bands of nitric oxide

Abstract

The excitation of several pronounced γ bands of NO by electron impact was studied from threshold to 1000 eV. A high optical efficiency was achieved by using an ellipsoidal collision chamber with mirrored interior surfaces. The interaction volume viewed was located at one of the foci of the ellipsoid. A 0.25 m double monochromator and single photon counting techniques were employed to monitor molecular band intensities. The optical sensitivity between 2000 and 4000 Å was obtained with the molecular branching ratio method by monitoring 1NG CO+, 1NG N+2, 2PG N2 band intensities and suitable progressions in the γ system of NO. Second order effects were avoided by low NO densities (∼10−1 torr) in the collision chamber. No ionization gauges were used during measurement, thus eliminating the possible dissociation of NO and subsequent formation of N2. Absolute cross sections for γ bands were obtained by normalizing to the 2PG (0,0) band of N2. For this purpose, a known mixture of NO and N2 was prepared in a gas handling manifold using a manometer. For the unambiguously identifiable (0,1), (0,2), (1,0), (1,5), and (2,7) γ bands of NO, the cross sections peaked near 18 eV and had values of 2.2, 1.8, 6.3, 1.3, and 0.57×10−19 cm2, respectively, with a possible error of 25%. The relative peak cross sections agree with calculated band intensities within 20%.