Rotational transitions of COH+ and He: New interaction potential, bound states, scattering and pressure broadening cross-sections

We present new calculations of a metastable isomer of HCO+, i.e. COH+ in collision with He. The COH+ has been suggested as an alternative molecular hydrogen tracer, which makes it of great interest for astrophysical studies. COH+ was first observed in astronomical space towards SgrB2 with the observation of J=1→0, J=2→1 and J=3→2 lines. Calculations are based on new ab initio potential energy surfaces (PES) of charged complex COH+-He using the CCSD(T) in conjunction with aug-cc-pVQZ basis set. The PES has a well depth of -836.5 cm−1 towards H-end at the COH+−He distance (R) of 2.9 ˚A in linear orientation. To test the new PES, the calculations of the bound-state are carried out and pressure broadening cross-sections of COH+ with He collisions are computed for kinetic energies up to 150 cm−1 using the accurate close-coupling method. Further, the pressure broadening and shift coefficients have been calculated from the corresponding real and imaginary parts of cross-sections for the first six rotational transitions. The data obtained is found to be in the same order as the HCO+-He system. Further, we have computed the rate coefficients and compared the results with the reported COH+-He and HCO+-He data. The results generated by this study is believed to be useful for both laboratory and future astrophysical research.