The kinetics of free radicals generated by IR laser photolysis. II. Reactions of C 2(X 1Σ +g), C 2(a 3Π u), C 3(X̄ 1Σ +g) and CN(X 2Σ +) with O 2

Abstract

The 300 K reactions of O 2 with C 2(X 1Σ + g), C 2(a 3 Π u), C 3(X̄ 1Σ + g) and CN(X 2Σ +), which are generated via IR multiple photon dissociation (MPD), are reported. From the spectrally resolved chemiluminescence produced via the IR MPD of C 2H 3CN in the presence of O 2, CO molecules in the a 3Σ +, d 3Δ i, and e 3Σ − states were identified, as well as CH(A 2Δ) and CN(B 2Σ +) radicals. Observation of time resolved chemiluminescence reveals that the electronically excited CO molecules are formed via the single-step reactions C 2(X 1Σ + g, a 3Π u) + O 2 → CO(X 1Σ + + CO(T), where T denotes are electronically excited triplet state of CO. The rate coefficients for the removal of C 2(X 1Σ + g) and C 2(a 3Π u) by O 2 were determined both from laser induced fluorescence of C 2(X 1Σ + g) and C 2(a 3Π u), and from the time resolved chemiluminescence from excited CO molecules, and are both (3.0 ± 0.2)10 −12 cm 3 molec −1 s −1. The rate coefficient of the reaction of C 3 with O 2, which was determined using the IR MPD of allene as the source of C 3 molecules, is <2 × 10 −14 cm 3 molec −1 s −1. In addition, we find that rate coefficients for C 3 reactions with N 2, NO, CH 4, and C 3H 6 are all < × 10 −14 cm 3 molec −1 s −1. Excited CH molecules are produced in a reaction which proceeds with a rate coefficient of (2.6 ± 0.2)10 −11 cm 3 molec −1 s −1. Possible reactions which may be the source of these radicals are discussed. The reaction of CN with O 2 produces NCO in vibrationally excited states. Radiative lifetime of the Ā 2Σ state of NCo and the Ā 1Π u(000) state of C 3 are reported.