Calculations of rate coefficients for the fast reaction of a structureless ion with a dipolar linear molecule in a 2Π electronic state are presented. The rotationally adiabatic capture theory is used together with a simple classical electrostatic potential. An analytical formula is derived for the rate coefficient in the low temperature limit. The reaction of H 3+ with OH(X2Π) is taken as an example. For temperatures less than 90 K, the rate coefficients differ from those calculated for molecules in 1Σ states. The most interesting new prediction is that the rate coefficient for the reaction of a 2Π polar molecule with an ion is proportional to T-1/2 for temperatures close to absolute zero. © 1992 American Institute of Physics.
