Negative-Ion–Molecule Reactions in N2O

Abstract

The relative concentrations of various negative ions present following electron attachment to N2O have been measured as a function of pressure. The ions were identified using a quadrupole mass spectrometer coupled to a drift tube operating at pressures between 0.3 and 8 torr. The dependence on E / p of the total negative-ion current is consistent with the change from a three-body to a two-body attachment process at E / p values near 1 V cm−1·torr−1. Using purified N2O at E / p = 10 V cm−1·torr−1, the O− ions formed by attachment undergo a series of ion–molecule reactions with the N2O to form ions with masses corresponding to NO−, N2O2−, NO2−, and N3O2−. Several reaction schemes are considered, and a fit to the observed pressure dependence is obtained by postulating the presence of intermediate excited states of N2O2− and N3O2− with lifetimes of 4 × 10−7 and 10−7 sec.