Vibrational and rotational energy distributions of CH3 and IF formed in the reactions of F atoms with CH4 and CH3I

Abstract

The two reactions F+CH4→CH3+HF (1) and F+CH3I→CH3+IF (2) have been investigated by using time-resolved diode laser absorption spectroscopy to probe the reaction products CH3 and IF. The fluorine atoms have been generated by the pulsed CO2 laser photolysis of SF6 in the presence of CH4 or CH3I at a total pressure of 5 Pa. Rotational lines of CH3 in the v2 =1–0, 2–1, and 3–2 bands (out-of-plane bending vibration) and those of IF in the v=1–0, 2–1, 3–2, 4–3, 5–4, and 6–5 bands have been observed and analyzed to determine time-dependent product energy distributions. No clear evidence for population inversion has been found in the vibrational levels of both CH3 and IF. Nascent vibrational distributions of v2=0:1:2 of CH3 are 1:0.36:0.15 for reaction (1) and 1:0.32:0.14 for reaction (2), and that of IF v=0:1:2:3:4:5 is 1:0.70:0.40:0.22:0.10:0.04. The nascent CH3 produced in reaction (1) is rotationally cold (around room temperature) and only 3% and 2% of total available energy are partitioned to the ν2 vibrational mode and rotational motion of CH3, respectively. The vibrational and rotational energy distributions of CH3 and IF produced in reaction (2) have been well reproduced by a statistical model calculation.