Electron attachment and detachment in nitric oxide

Abstract

The attachment coefficient and drift velocity of electrons in nitric oxide have been measured in a pulsed drift tube, over a reduced field range between 6 × 10–18 and 2 × 10–16 V cm2 molecule–1, at gas densities of ca. 3 × 10+18 molecule cm–3 and ambient temperatures between 293 and 493 K. The resultant attachment frequency, described as second order in nitric oxide pressure at room temperature, reached a peak value of 12 × 10–31 cm6 molecule–2 s–1 at 0.2 eV electron energy, falling off at higher and lower energies. The thermal rate found by extrapolation is 8 ± 2 × 10–31 cm6 molecule–2 s–1. At higher temperatures the measured coefficient fell, indicating the occurrence of detachment reactions. The detachment rate was measured in separate experiments using a d.c. drift tube and mass filter and found to be 5 ± 1 × 10–12 cm3 molecule–1 s–1, for near thermal ions. Comparison of the measured attachment and detachment rates with the statistical mechanical formula for the equilibrium constant yields a value of 0.026 ± 0.02 eV for the electron affinity of nitric oxide.The only stable ion formed in NO was mass 46, NO–2, formed by subsequent ion molecule reactions from the initial product NO–. In NO + O2 mixtures the rate of the following reaction was measured: NO–3+ NO → NO–2+ NO2, k= 3 × 10–15 cm3 molecule s–1. From equilibrium considerations, it is deduced using the value of this rate constant that the electron affinity of NO3 exceeds that of NO2 by at least 1.13 eV.