Rotational cooling of aniline in axis-symmetric and planar pulsed supersonic expansions

Abstract

Laser-induced fluorescence (LIF) has been used to measure rotational temperatures, TR, of the aniline molecule in axis-symmetric and planar pulsed supersonic expansions of He, Ne, and Ar. The rotational contours of the O–O band of the 1B2 ← 1A1 transition of aniline were measured by LIF and were fitted by computer-simulated rotational contours, resulting in the determination of TR. For axis-symmetric jets expanded from a 0.06 cm nozzle at stagnation pressures p = 100–2300 Torr, we find TR to vary from 15 ± 2 K to 2.2 ± 0.2 K. The degree of rotational cooling increases in the order of [Formula: see text]. The pressure dependence of [Formula: see text] for Ar (in the range p = 100–1000 Torr) and [Formula: see text] for He (in the range p = 300–2300 Torr), manifesting the implications of the velocity slip effect. Evidence for extensive formation of van der Waals complexes in the aniline–Ar system at p ≥ 1000 Torr was inferred from the saturation of TR with increasing p in this range. In planar supersonic jets of Ar expanded from a 0.2 × 35 mm nozzle slit at p = 5–200 Torr, the rotational temperature varied in the range TR = 90 ± 10 K to 12 ± 2 K, exhibiting the dependence [Formula: see text] Additional diagnostic information on planar jets was obtained for the dependence of the rotational temperature on the distance from the nozzle slit.