Abstract

Rate constants for the vibrational deactivation of ¹²C¹⁶O by H₂, d₂, and ⁴He have been determined by the laser-induced fluorescence in the gas phase at low temperatures. The rate constants for ¹²C¹⁶O (v = 1) − H₂ and ¹²C¹⁶O (v = 1) − D₂ have been measured down to 35 K and those for ¹²C¹⁶O (v = 1) − ⁴He to 40 K. This excitation of our previous data has been made possible by the adoption of a frequency-doubled CO₂ laser. The rate constants for ¹²C¹⁶O (v = 1) — H₂ and ¹²C¹⁶O (v = 1) — D₂ show a minimum at 50 K, whereas that for ¹²C¹⁶O (v = 1) — ⁴He steadily decreases with lowering temperature throughout the range studied here. The rate constants for the ¹²C¹⁶O—H₂ are consistently higher than those for ¹²C¹⁶O—D₂. It is suggested that upturns for H₂ and D₂ are due to attractive forces becoming important at low temperatures. This upturn in the rate constants is markedly more pronounced for ¹²C¹⁶O—D₂ than for ¹²C¹⁶O—H₂. This is consistent with the effects of the attractive terms of the potential, which are equal for both systems, being more pronounced for the systems with the smaller rate constant.

© 1996 Optical Society of America