The effect of low frequency vibrations in CH4on the rate constant for the reaction of O+2(Xthinsp;2Pgr;g,v=0) with CH4

摘要

The rate constant for the reaction of O+2with CH4has been measured as a function of average centerhyphen;ofhyphen;mass kinetic energy, lang;KEcmrang;, at several temperatures over the range 93ndash;545 K. The rate constant decreases with increasing lang;KEcmrang; at low lang;KEcmrang; and increases at higher lang;KEcmrang;; the position of the resulting minimum depends on temperature. We have observed small differences in the rate constants measured at the same total lang;KEcmrang; but at different temperatures in the low temperature regime (Tle;300 K). These differences, i.e., decreasing rate constants with increasing temperature, are discussed in terms of the possibility of a rate constant which is dependent upon rotational energy. At higher temperatures, 430 and 545 K, we find that the rate constant is significantly larger than that measured at lower temperatures at a given lang;KEcmrang;. This enhanced reactivity is attributed to vibrational excitation in the CH4. From these data, we derive a rate constant for vibrationally excited CH4(in the low frequency modes) that is approximately a factor of 20 greater than the rate constant for the ground vibrational state. The data disagree with an early study of this type at low temperature. The disagreement is discussed, and arguments are presented which indicate that the earlier data are in error at low temperature with an applied drift field. The use of these data for deriving effective reaction temperatures in other nonthermal experiments is also discussed.