Ab initio study of spectroscopic properties at anharmonic force fields of LiNH₂

This work presents a systematic investigation of the spectroscopic properties at anharmonic force fields of ground electronic state ([Formula: see text]) of LiNH₂, which are calculated using second-order Møller-Plesset perturbation theory (MP2) and density functional theory (DFT) with hybrid GGA and meta-hybrid GGA (M06-2X) exchange-correlation functional. Two high angular momentum basis sets of 6-311+g (2d, p) and 6-311++g (3df, 2pd) are used. The equilibrium geometries, ground-state rotational constants, harmonic frequencies, and quartic and sextic centrifugal distortion constants of LiNH₂ are calculated and compared with corresponding experimental or theoretical data. The predicted accuracy of the calculated constants has been confirmed by analyzing the deviations with respect to experiment. In addition, the anharmonic constants, vibration-rotation interaction constants, force constants, and Coriolis coupling constants of LiNH₂ are firstly obtained. The infrared spectrum is predicted and together with the first prediction on the higher-order anharmonic constants contributes to a better understanding of the vibrational and rotational characteristics of LiNH₂, thus revealing its internal structure. Graphical abstract The IR spectra and the magnified IR spectra at 3500 cm^-1 in harmonic approximations of LiNH₂ using B3P86, M06-2X and MP2 methods combining with 6-311++g(3df,2pd).