Rotational excitation of C(2)(X(1)Σ(g)(+)) by para- and ortho-H(2)

A new four dimensional (4D) potential energy surface for the C(2)(X(1)Σ(g)(+))–H(2) van der Waals system is generated. The potential was obtained from a multi-reference internally contracted configuration-interaction method including the Davidson correction (MRCI+Q). The four atoms were described using the augmented correlation-consistent quadruple zeta (aug-cc-pVQZ) basis sets. Both molecules were treated as rigid rotors. Close-coupling calculations of the inelastic integral cross sections of C(2) in collisions with para-H(2)(j(H(2)) = 0) and ortho-H(2)(j(H(2)) = 1) were also carried out at low energies. After Boltzmann thermal averaging, rate coefficients were obtained for temperatures ranging from 5 to 100 K. The rate coefficients for collisions with ortho-H(2) are significantly larger than the rate coefficients for collisions with para-H(2).