Electronic Curves Crossing in Methyl Iodide by Spin–Orbit Ab Initio Calculation

An ab initio investigation of electronic curve crossing in a methyl iodide molecule is carried out using Spin–Orbit multiconfigurational quasidegenerate perturbation theory. The one-dimensional rigid potential curves and optimized effective curves of low-lying states, including Spin–Orbit coupling and relativistic effects, are calculated. The Spin–Orbit electronic curve crossing between 3Q0+and 1Q1, and the shadow minimum in potential energy curve of 3Q0+ at large internuclear distance are found in both sets of the curves according to the present calculations. The crossing position is in the range of RC–I = 0.2370 ± 00001 nm. Comparisons with other reports are presented. (atomic and molecular physics)