Vibration-rotation energy levels and corresponding eigenfunctions of 12CH4 up to the tetradecad

In this paper, we report the vibration-rotation energy levels of methane (12CH4) calculated using the latest version of the global effective Hamiltonian developed in Dijon [B. AMYAY et al.. J. Chem. Phys., 148, 134-306 (2018)]. 238,429 vibration-rotation energy levels are calculated rotationally up to J= 50 and vibrationally up to the Tetradecad ( ≈  6200 cm−1). The corresponding wavefunctions mixings are also investigated in this work. The knowledge of both energy levels and wavefunctions mixings are essential for simulating high-resolution spectra of methane of astrophysical and atmospheric interests. An evidence of distinct regular and oscillatory contributions, is observed in the number of vibration-rotation levels of methane. This can be fully understood using the generating functions presented by Sadovskií and Zhilinskií [J. Chem. Phys. 103, 10-520 (1995)].