Revisiting the Formation of HeH + in the Planetary Nebula NGC 7027

Abstract

From four independent calculations using three different theoretical approaches, rate coefficients for the formation of HeH + via the radiative association of He + and H were computed. Good agreement is found between our new calculations and prior results obtained two decades ago for kinetic temperatures between ∼800 and 20,000 K. This finding is inconsistent with a recent claim in the literature of a wide variation in published values and establishes the robustness of our knowledge of this process for the formation of HeH + . The implications of the current results to the first detection of HeH + and its modeled abundance in the planetary nebula NGC 7027 are discussed.