Capture Collisions of Polyynide Anions with Hydrogen Atoms: Effect of the Ion Dipole, Quadrupole, and Anisotropic Polarizability

• Classical capture rates for dipolar and quadrupolar ions are modeled.
• Capture rates for C2nH− (n = 2–4) + H collisions are calculated.
• The polarizability, dipole, and quadrupole of the ion all contribute significantly.

Classical capture rate constants are calculated for a molecular ion with a dipole moment, quadrupole moment, and anisotropic polarizability colliding with a neutral polarizable atom. The free-energy effective potential method is used to average the potential energy over the interaction angle. Numerical methods are used to calculate the effective potential from the full anisotropic induction potential energy function, to solve for the position of the centrifugal barrier, and to determine the thermal rate constants. The capture collision model is applied to the reactions of polyynide anions, HC4−, HC6−, and HC8−, with atomic hydrogen, which are of interest in astrophysical environments, using calculated multipole moments and anisotropic polarizabilities. The dipole moment, quadrupole moment, and polarizability of the ion each contribute significantly toward the total predicted classical capture collision rates for these systems.

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