Vibrational quenching of NO+(v) ions in collision with H2, D2, and O2

Abstract

The vibrational quenching rate constants for NO+(v), predominantly in the v=1 state, have been measured at 200 and 293 K in collisions with H2 and D2 and at 200, 293, and 458 K with O2. The rate constants are all very low, corresponding to quenching probabilities ∼10−4. The low rate constants reflect very shallow attractive potential wells. In the case of H2 and D2 this is a consequence of their low polarizabilities. In the case of O2, repulsive chemical interactions offset the electrostatic attraction to yield a shallow attractive well. This is a consequence of the singlet NO+ and triplet ground state O2 not approaching on the attractive NO+3 ground state potential surface, which is a singlet. The temperature dependences of the quenching rate constants are generally slight, indicating that the collision energies are in a range comparable to the attractive well depth and that the quenching is not strongly dominated by either the attractive forces, which would give a negative energy dependence, or by the repulsive forces which would give a positive energy dependence.