Time-Resolved Observations Of Vibrationally Excited No X (2)Pi (V ') Formed From Collisional Quenching Of No A (2)Sigma(+) (V=0) By No X (2)Pi: Evidence For The Participation Of The No A (4)Pi State

Time-resolved observations have been made of the formation of vibrationally excited NO X (2)pi (v ') following collisional quenching of NO A (2)sigma(+) (v = 0) by NO X (2)pi (v = 0). Two time scales are observed, namely a fast production rate consistent with direct formation from the quenching of the electronically excited NO A state, together with a slow component, the magnitude and rate of formation of which depend upon NO pressure. A reservoir state formed by quenching of NO A (2)sigma(+) (v = 0) is invoked to explain the observations, and the available evidence points to this state being the first electronically excited state of NO, a (4)pi. The rate constant for quenching of the a (4)pi state to levels v ' = 11-16 by NO is measured as (8.80 +/- 1.1) x 10(-11) cm(3) molecule(-1) s(-1) at 298 K where the error quoted is two standard deviations, and from measurements of the increased formation of high vibrational levels of NO(X) by the slow process we estimate a lower limit for the fraction of self-quenching collisions of NO A (2)sigma(+) (v = 0) which lead to NO a (4)pi as 19%.