Appearance potentials and transition probabilities for electron impact ionization of CO and CO⁺

Abstract

Electron impact ionization of CO in a mass spectrometer at electron currents of up to 170 μA and pressures of up to 5 × 10-5 torr has been used to study electron collision with CO+ trapped in a space-charge well in the electron beam. The processes observed are as follows: Appearance potential (v) Transition probability (×10-4) (1) CO → CO+ (x 2Σ+) → C+ 14.0 1.5 (2) CO → CO+ (x 2Σ+) → O+ 14.0 0.43 (3b) CO+ (A 2IIi) → CO2+ 25 0 ± 0.4 17 (4b, c) CO+ (x 2Σ+) → CO+ (c 2Σ+) → CO2+ 15.9 ± 0.7 0.14 (5) CO → C+ + O- 20.5 ± 0.7 (6) CO → C+ + O(3P) 22 6 ± 0.7 345 (8) CO → O+ + C(?) 19 ± 1 145 (10) CO → CO2+ (41.8) 11 relative to CO → CO+ at 14.01 v with a transition probability of 1. From (3b) the vertical ionization potential for CO → CO+ (A 2IIi) is 16.8 ± 0.4 ev and the cross section for (3b) is 58 ± 30 A2 at 30 ev. From (4b, c) the vertical ionization potential for CO->CO+ (c 2Σ+) is either 25.9 ± 7 ev or 29.9 ± 7 ev, and the product of the cross sections for (4b) and (4c) is of the order of 40 A4.