Interaction of C 2 H with molecular hydrogen: Ab initio potential energy surface and scattering calculations.

The potential energy surface (PES) describing the interaction of the ethynyl (C2 H) radical in its ground X̃2 Σ+ electronic state with molecular hydrogen has been computed through restricted coupled cluster calculations including single, double, and (perturbative) triple excitations [RCCSD(T)], with the assumption of fixed molecular geometries. The computed points were fit to an analytical form suitable for time-independent quantum scattering calculations of rotationally inelastic cross sections and rate constants. A representative set of energy dependent state-to-state cross sections is presented and discussed. The PES and cross sections for collisions of H2 (j = 0) are compared with a previous study [F. Najar et al., Chem. Phys. Lett. 614, 251 (2014)] of collisions of C2 H with H2 treated as a spherical collision partner. Good agreement is found between the two sets of calculations when the H2 molecule in the present calculation is spherically averaged.