Rovibrational calculations for CH_3~+-Rg (Rg=He,N): The prototype disk-and-ball dimer

摘要

Rovibrational calculations in the intramolecular ground vibrational states of the CH_3~+-Rg dimers, Rg-He and Ne, are carried out on intermolecular ab initio potnetial energy surfaces (PESs) calculated at the MP2 level of theory using a basis set of aug-cc-pVTZ quality. The internal CH_3~+coordinates in the dimer are kept frozen at the optimal monomer coordinates (D_(3h) symmetry, rigid monomer approximation). The three-dimensional (3D) intermolecular PESs of both dimers feature pronounced global minima at p-bound equilibrium structures: the Rg atom is attached to one side of the 2p_z orbital of the central C atom along the C_3 symmetry axis (C_(3v) symmetry). The intermolecular C-He and C-Ne bonds are characterized by separations of R_e=1.93 and 2.21 A and dissociation energies of D_e=672 and 935 cm~(-1), respectively. The PESs of these prototype disk-and-ball dimers reveal substantial angular-radial coupling in the region of the global minimum which leads to significant differneces between the equilibrium and vibrationally averaged separations, R_e and R_0. The 3D rovibrational calculations on the rigid monomer PESs yield R_0 = 2.54 and 2.43 A and D_0=193 and 474 cm~(-1) for CH_3~+-He and CH_3~+-Ne, respectively. In general, the spectroscopic constants derived fro the ground vibrational states of both complexes are in good agreementwith recent spectrscopic data obtained by infrared photodissociation spectroscopy.