Figure shows the reaction path diagram for this isomerization reaction, complemented by the optimized geometric parameters of the stationary points. Additionally, some prior theoretical results are included for comparison. As shown, the transition state involves the rotation of the methyl group, migrating from the nitrogen side of the cyano group to the carbon side (through a 1,2 methyl-shift), which results the breaking of the CN bond and the simultaneous formation of the CC bond. Namely, the structure transformation during the reaction is mainly featured through the angle θCNC. The molecule manifests as CH3NC when θCNC reaches 180° and transitions to CH3CN at 0°. CH3NC and CH3CN have nearly the same CH bond lengths for the methyl group, where these values are slightly lower than those obtained from the spectroscopic experiments, with a maximum deviation of 0.017 Å. And the three CH bond lengths in the methyl group do not remain the same in the transition state, but are slightly smaller than those in the reactant and product. The CN bond length of the cyano group increases by 0.023 Å from the reactant to the transition state and subsequently decreases by 0.037 Å from the transition state to the product, leading to an overall decrease of 0.014 Å. The CN and NC bond lengths are 1.424 Å, 1.172 Å for CH3NC, while CH3CN exhibits CC and NC bond lengths of 1.463 Å and 1.158 Å, respectively. These values are in good agreement with the experimental results, 1.424 Å and 1.166 Å for CH3NC, and 1.458 Å and 1.157 Å for CH3CN.