Ab initio potential energy surfaces for the study of rotationally inelastic collisions

The four potential energy surfaces (PESs) associated, respectively to 1A′, 3A′, 1A″ and 3 A ″ states correlating to the interacting CH ( X 2 Π ) + H ( 2 S ) system, were determined using the aug-cc-pVQZ basis set, and multireference internally contracted configuration-interaction (MRCI) calculation method including the Davidson correction. The CH bond length was fixed at the equilibrium value of the X 2 Π ground state. The PES of the A ′ state considerably differs from that of the A ″ state. The ab initio calculated interaction energies of the A ′ and A ″ PESs for each spin multiplicity were fitted analytically on the basis of Legendre polynomials.