Multidimensional Morse/Long-Range Potential Energy Surface and Predicted Rotational Spectra of the CH4-N2 Complex.

A five-dimensional intermolecular potential energy surface (PES) was developed for the CH₄-N₂ complex with methane fixed at its experimental equilibrium geometry. Intermolecular potential energies were calculated using the explicitly correlated coupled-cluster [CCSD(T)-F12] approach and the augmented correlation-consistent aug-cc-pVTZ basis set. A multidimensional Morse/long-range function was fitted to 49,385 ab initio points, yielding an analytic PES with a root-mean-square deviation of 0.441 cm^-1. Rovibrational levels and corresponding wave functions were determined using a discrete variable representation and angular finite basis representation method in conjunction with the Lanczos algorithm. Furthermore, rotational transition frequencies for the CH₄-N₂ complex were predicted for the first time. The cross second virial coefficient for CH₄-N₂ was computed to assess the PES, showing reasonable agreement with the existing experimental data.