Ab initio potential energy surface and intermolecular vibrational frequency of C3-He complex

The intermolecular potential energy surface for C3-He complex has been constructed using supermolecular CCSD(T) and MP4 methods. The potential surfaces have been calculated for 27 values of R ranging from 2.8 to 8.0 angstrom and 19 values of equally spaced between 0 degrees and 180 degrees. Both CCSD(T) and MP4 potentials have similar global behaviors. The global minimum in each of the potentials corresponds to the slightly distorted T-shaped geometry. On the basis of these two potentials, the intermolecular vibrational energies and wavefunctions were calculated. The energy level pattern of the vdW vibrational states was predicted for C3-He complex. The zero point bending motion of this complex has a range of 180 degrees. The calculated fundamental frequency of vdW bending is 3.16 cm-1 at CCSD(T) level, and 5.38 cm-1 at the MP4 level. In addition, we have also constructed the intermolecular potential energy surface with C3 bending coordinate of 160 degrees by using supermolecular CCSD(T) method. Two local minima including arrow-shaped and Y-shaped configurations were determined. The rotational constants of three C3-He structures including T-shaped, arrow-shaped and Y-shaped configurations at CCSD(T) level were also reported.