Interaction of rigid C 3 N - with He: Potential energy surface, bound states, and rotational spectrum.

A two-dimensional rigid rotor model of the potential energy surface is developed for the collision of C3 N- with He. Ab initio calculations are performed at the coupled cluster level with single and double excitations and using a perturbative treatment of triple excitations. An augmented correlation consistent polarized valence quadruple zeta basis set complemented with a set of mid-bond functions is chosen for these calculations. The global T-shaped minimum (De = 62.114 cm-1 ) is found at the intermolecular distance R = 6.42 a0 . A secondary minimum (De = 41.384 cm-1 ) is obtained for the linear configuration C3 N- -He and for R = 9.83 a0 . Calculations of the rovibrational bound states are carried out by using a discrete variable representation method based on Sturmian functions. The first theoretical prediction of the absorption spectra for the He-C3 N- complex in the microwave region is also provided.