Some Features of the CH3NC→CH3CN Potential Surface

Nonempirical self‐consistent‐field calculations are reported for about 75 points on the potential surface for the ${\mathrm{CH}}_3\mathrm{NC}\to {\mathrm{CH}}_3\mathrm{CN}$ isomerization. Due to interest in the possible non‐RRKM behavior of CH₃NC, the magnitude of the barrier to rotation of the methyl group is examined as a function of the reaction coordinate. The transition state or saddle point geometry is determined by minimizing the potential energy with respect to five geometrical parameters and maximizing with respect to a sixth. The geometries of CH₃NC and CH₃CN are also predicted and found to agree closely with experiment. Finally, it is established that, contrary to semiempirical results, the present theoretical approach does not predict the existence of a relative minimum in the reaction coordinate.