Collisional excitation of C2H(X2Σ+) by para-H2(j = 0): Fine-structure resolved transitions

We report theoretical cross sections and rate coefficients for the collisional excitation of C2H(X2Σ+) by para-H2(j =0). The two molecules are treated as rigid rotors. The intermolecular interaction is described by a two-dimensional potential energy surface (PES) averaged over H2 orientations and based on RCCSD(T) calculations with aug-cc-pVTZ basis sets plus bond functions. Close-coupling calculations of collisional excitation cross sections for the first 25 fine-structure levels of C2H yielded rate coefficients up to 100 K. The results show marked differences with recent excitation rate coefficients determined for C2H with He as the collision partner.