Molecular beam chemiluminescence XI: kinetic and internal energy dependence of the NO + O 3 → NO 2*,→ NO 2‡ reaction

Abstract

Seeded supersonic NO beams were used to study the kinetic energy dependence of both the electronic (NO 2 *) and vibrational (NO 2 ‡) chemiluminescence of the NO + O 3 reaction. In addition the electronic CL is found to be enhanced by raising the NO internal temperature. This is shown to be due to enhanced reactivity of the NO( 2Π, 3 2 ) fine structure component. By difference NO( 2Π 1 2 ) is concluded to yield predominantly groundstate NO 2 ‡. The excitation function for NO 2 * formation from NO( 2Π 3 2 ) is of the form σ 3 2 ( E) = C(E/E 0 - 1) n over the 3–6 kcal energy range where n = 2.4 ± 0.15, C = 0.163 Å 2 and E 0 = 3.2 ± 0.3 kcal/mole. Vibrational IR emission from NO 2 ‡ has an energy dependence different from electronic NO 2 * emission, confirming that emitters are formed predominantly in distinct reaction channels rather than via a common precursor (either NO 2 * or NO 2 ‡). The short wavelength cutoff of the CL spectra recorded at elevated collision energies E ⩽ 15 kcal/mole corresponds to the total available energy. These and literature results are discussed in the light of general properties of the (generally unknown) ONO 3 potential energy surfaces. The formation of electronically excited NO 2 * rather than energetically preferred O 2 ( 1 Δg) (Gauthier and Snelling) can be rationalized in terms of surface hopping near a known intersection of potential energy surfaces more easily than by vibronic interaction in the asymptotic NO 2 product.