Rovibrational calculations for CH3+–Rg (Rg=He,Ne): The prototype disk-and-ball dimer

Abstract

Rovibrational calculations in the intramolecular ground vibrational states of the CH3+–Rg dimers, Rg=He and Ne, are carried out on intermolecular ab initio potential energy surfaces (PESs) calculated at the MP2 level of theory using a basis set of aug-cc-pVTZ quality. The internal CH3+ coordinates in the dimer are kept frozen at the optimal monomer coordinates (D3h 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 2pz orbital of the central C atom along the C3 symmetry axis (C3v symmetry). The intermolecular C–He and C–Ne bonds are characterized by separations of Re=1.93 and 2.21 Å and dissociation energies of De=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 differences between the equilibrium and vibrationally averaged separations, Re and R0. The 3D rovibrational calculations on the rigid monomer PESs yield R0=2.54 and 2.43 Å and D0=193 and 474 cm−1 for CH3+–He and CH3+–Ne, respectively. In general, the spectroscopic constants derived for the ground vibrational states of both complexes are in good agreement with recent spectroscopic data obtained by infrared photodissociation spectroscopy.