Distribution of internal states of CO from O (D-1) + CO determined with time-resolved Fourier transform spectroscopy

Abstract

Following collisions of O (D-1) with CO, rotationally resolved emission spectra of CO (1 e V e 6) in the spectral region 1800-2350 cm(-1) were detected with a step-scan Fourier transform spectrometer. O (D-1) was produced by photolysis of O-3 with light from a KrF excimer laser at 248 nm. Upon irradiation of a flowing mixture of O-3 (0.016 Torr) and CO (0.058 Torr), emission of CO (v <= 6) increases with time, reaches a maximum similar to 10 mu s. At the earliest applicable period (2-3 mu s), the rotational distribution of CO is not Boltzmann; it may be approximately described with a bimodal distribution corresponding to temperatures similar to 8000 and similar to 500 K, with the proportion of these two components varying with the vibrational level. A short extrapolation from data in the period 2-6 As leads to a nascent rotational temperature of similar to 10170 +/- 600 K for v = 1 and similar to 1400 +/- 40 K for v = 6, with an average rotational energy of 33 (6 kJ mol(-1). Absorption by CO (v = 0) in the system interfered with population of low J levels of CO (V) 1). The observed vibrational distribution of (v = 2):(v = 3):(v = 4):(v = 5):(v = 6) = 1.00: 0.64: 0.51: 0.32: 0.16 corresponds to a vibrational temperature of 6850 +/- 750 K. An average vibrational energy of 40 (4 kJ mol(-1) is derived based on the observed population of CO (2 e V e 6) and estimates of the population of CO (V) 0, 1, and 7) by extrapolation. The observed rotational distributions of CO (1 <= v <= 3) are consistent with results of previous experiments and trajectory calculations; data for CO (4 <= v <= 6) are new.