Vibrational Deactivation in Methane Mixtures

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Abstract
The vibrational relaxation of the bending modes of CH4 in mixtures with rare gases and diatomic molecules has been studied by laser‐excited vibrational fluorescence. The measuredenergy transfer probabilities cannot be understood, even qualitatively, in terms of simple theories of either vibration‐to‐translation energy transfer or vibration‐to‐rotation energy transfer. The data indicate that vibrational energy is transferred into translation, methane rotation, and collision partner rotation. The relative distribution among these degrees of freedom appears to vary greatly among the collision partners studied. Ethane was found to be an efficient catalyst for the vibrational relaxation of CH4. Since it is one of the major impurities in methane samples, this observation explains why some authors have observed relaxation times for “pure” CH4 less than 2 μsec·atm.