Temperature dependence of the quenching of vibrationally excited nitrogen by atomic oxygen

A photo-ionization detector for vibrationally excited nitrogen (N2*) has been used to obtain the rate of quenching of N2* by atomic oxygen in the temperature range 300°–723°K. The quenching rate coefficient was found to be 3.2 × 10−15 cm³ s−1 at 300°K, 1.3 × 10−14 cm³ s−1 at 463°K, 2.7 × 10−14 cm³ s−1 at 633°K, and 4.0 × 10−14 cm³ s−1 at 723°K. These rate coefficients are extremely large compared with the expected values for a conventional vibrational-translational (VT) energy transfer process in this temperature range. They are also large compared with the predictions of the vibrational relaxation theory developed by Fisher and Bauer for the N2-O system based upon crossing of covalent potential energy curves. The measured coefficients combined with higher temperature data obtained elsewhere with different experimental methods indicate that the VT process in the N2-O system is anomalously efficient over the range 300°–4500°K and has only a moderate temperature dependence. This result has important consequences in the upper atmosphere, where the effect of an efficient VT process involving N2 and O is to hold the atmospheric N2 vibrational temperature at or very near the ambient kinetic temperature, in agreement with the results of recent rocket probe experiments.