Selective hyperfine excitation of $N2H+$ by He: Potential energy surface, cross sections, and propensity rules Available to Purchase

We present potential energy surfaces for the $He-N2H+$ system adiabatically corrected for the zero-point motion along the intermolecular stretching vibrations $v1=0$ and $v1=1.$ The potentials are extended to shorter $He-N2H+$ separations which makes them useful for scattering calculations. Close coupling calculations of the spinless $S$ matrices for the rotational excitation of $N2H+$ by He are presented, and recoupling techniques to obtain collisional excitation cross sections between the $N2H+$ hyperfine levels are used. The propensity rules between hyperfine levels are investigated for the case where two nuclear spins are involved. It is found that the only well defined propensity rule is $ΔF=ΔF1=Δj$ and that calculations are required in order to obtain the relative intensities of the two-spin hyperfine cross sections.