Photoinitiated H + N2O reactions. N2O–HBr complexes and gas-phase, single-collision, arrested-relaxation conditions
Abstract
Several reactions are reported in which photolytically prepared ‘hot’ H atoms react with N2O. Under bulk (i.e. single-collision arrested-relaxation) conditions with H-atom kinetic energies of ca. 2.5 eV, intense OH (A2Σ→ X2Π) chemiluminescence is observed. The relative A 2Σ vibrational populations are (ν= 0)/(ν= 1)/(ν= 2)= 5/3/2. However, with N2O–HBr complexes, no such emission is observed, and OH (X2Π) is easily detected using LIF. In both cases, NH(X 3Σ) is observed using LIF, and the slightly colder rotational distribution obtained with complexes is attributed to simultaneous H–Br and H–N2O entrance channel repulsions. With N2O–HBr complexes, the [NH (X 3Σ)]/[OH(X2Π)] ratio is ca. 0.5, despite the 95 kcal mol–1 difference favouring OH + N2 over NH + NO. There is no evidence of products derived from O(1D) reactions via N2O photolysis. At lower H–atom kinetic energies (e.g. ca. 1.8 eV), there is no chemiluminescence, although OH (A 2Σ) is still energetically accessible.