Vibrational energy transfer in thermal methyl isocyanide isomerization. Relative cross sections in complex molecular systems
Relative energy transfer collision cross sections for several complex hydrocarbon and substituted hydrocarbon molecules have been determined in the methyl isocyanide thermal isomerization system. Particular interest was placed in the incremental cross sectional changes due to geometric isomerization in C6 hydrocarbons. Three generalizations are illustrated by the data. (1) Substitution for hydrogen in alkane molecules tends to increase their size. (2) Progressive branching of alkanes having constant carbon number causes a progressive decrease of the collision diameter. (3) Cyclization of the alkane chain decreases the effective size of the molecule. The energy transfer data are compared with viscosity-derived collision diameters where possible. A simple spherical model based on end-to-end carbon distances is proposed for systematizing the relative collision diameters of related complex molecules.