Energy transfer in thermal methyl isocyanide isomerization. A comprehensive investigation
The low-pressure thermal isomerization of methyl isocyanide has been studied at 280.5° in the presence of 109 different inert bath gases. Relative collisional activation-deactivation efficiencies β were measured. The attractive nature of the interaction is of importance: polarizability, dipole moment, and H-bonding ability of the bath molecule all seem to affect its efficiency. These experiments provide support for the view that vibrational energy transfer at high-energy levels of complex substrate molecules involves a quasi-statistical redistribution of internal energy of the collision complex. The efficiency increases in general with the number of transitional modes of the collision complex: a general correlation exists between β and the boiling point of the bath gas; but three subcorrelations are found for monatomic, diatomic and linear, and complex nonlinear molecules, respectively, which reflect the importance of dynamical considerations associated with angular momentum conservation in the energy-transfer process. Large amounts of energy are transferred per collision: 440 cm-1 for an inefficient bath molecule such as He, and in excess of 2000 cm-1 for operationally strong colliders such as the parent molecule. The role of the internal degrees of freedom of the bath molecule in energy transfer is not clear except for the parent molecule itself for which these seem to be active, but it is probable that lower vibration modes of some inerts play some role. Corrections to some earlier published data are given.
