Collisional quenching of highly rotationally excited NH (A 3Πi)

Abstract

Collisional removal of the v′=0 level of the A 3Πi state of the NH molecule has been studied as a function of rotational level with particular attention to high N′. Multiphoton dissociation of NH3 at 193 nm produces highly rotationally excited ground state NH (to N″=30), which is subsequently electronically excited with a pulsed dye laser, and quenching rate coefficients determined by the pressure dependence of the time-resolved fluorescence. Colliders investigated are NH3, CO, CH4, H2, and D2. The quenching rates at first decrease with increasing N′, but become nearly constant at highest N′. This is consistent with dynamic effects on an attractive, anisotropic surface. Radiative rates for A 3Πi were also determined and found to decrease with increasing N′ at a rate in excellent agreement with recent ab initio calculations.