Rotational excitation of protonated hydrogen cyanide (HCNH+) by He atom at low temperature

We report on ab initio coupled-cluster calculations of the interaction potential energy surface for the HCNH + –He complex. The aug-cc-pVTZ Gaussian basis, to which is added a set of bond functions placed at mid-distance between HCNH + center of mass and He atom is used. The HCNH + bonds length are set to their values at the equilibrium geometry, i.e., r e [HC]=1.0780 Å, r e [CN]=1.1339 Å and r e [NH]=1.0126 Å. The interaction energy presents a global minimum located below the HCNH + –He dissociation limit. Using the interaction potential obtained, we have computed rotational excitation cross sections in the close-coupling approach and downward rate coefficients at low temperature ( T ≤120 K). It is expected that the data worked out in this study may be beneficial for further astrophysical investigations as well as laboratory experiments.