Vibrational relaxation of N2 by collision with He atoms

A quantum mechanical study of vibrational relaxation in the collision of N₂ with ³He and ⁴He is reported. An ab initio potential energy surface has been computed using the coupled electron pair approximation with an extended basis set. Cross sections for v=1 → 0 vibrational relaxation have been calculated on this surface by using the centrifugal sudden approximation (CSA). The calculated vibrational relaxation rate coefficients show a very encouraging agreement with those measured in laser fluorescence experiments for the temperature range 82-291 K. Over this temperature range the rate coefficients increase by a factor close to 100. The CSA computations are also used to test the accuracy of the vibrational close coupling, rotational infinite order sudden, and the breathing sphere approximations.