PO+-He collision: ab initio potential energy surface and inelastic rotational rate coefficients

Computations involving quantum dynamics are performed to attain cross-sections corresponding to rotational de-excitation and excitation rates of the PO+ species including four rotational lines recently detected in the interstellar molecular clouds. New ab initio potential energy surface (PES) for PO+-He collision is constructed by using CCSD(T) method and basis set extrapolated to complete basis set limit (CBS) considering a rigid rotor approximation. The PES is then trained to create neural network (NN) model to construct an augmented surface with angular coordinates at 1 degrees intervals. The PES has a global minimum located at theta = 110 degrees and R = 3.1 angstrom. An analytical fitting is performed on the NN surface to obtain the first 41 radial coefficients needed to solve the equations of the coupled-channel method. The essentially precise close coupling approach is used to compute the rotational (de-)excitation cross-sections till 1400 cm(-1) with rotational states converged up to 26. Further, these cross-sections are thermally averaged to get the rate coefficients for various rotational transitions till 200 K. The propensity rule favours the odd transitions (Delta j = 1) for the current study. The rate for the transition 5 -> 4 is found to be higher than transition 1 -> 0 by a factor of 3.1 at T = 20 K that decreases to 2.1 at T = 100 K.