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.