Absolute absorption cross sections at high resolution in the A2Πi – X2Πi band system of ClO

Abstract

Chlorine monoxide (ClO) has been produced at temperatures near 315 K in a fast-flow system at total pressures (of argon diluent) in the range 1.0–2.0 mm Hg. The transmittance of ultraviolet radiation has been determined with a spectral resolution of 0.0054 nm for all 35ClO ν′–0 A2Π3/2 – X2Π3/2 sub-bands in the range 3 ≤ ν′ ≤ 12 (305.9–274.9 nm). The ClO column density obtained with 8 or 12 traversals of the radiation along an 80 cm cell was in the range 1.0–2.0 × 1017 cm−2.The experimental transmittance profiles for each sub-band have been reproduced closely by synthetic spectrum calculations. The parameters required as input to the programs were optimized by nonlinear least-squares techniques. The fitted (Lorentzian) linewidths are on average more than double those previously reported from visual estimates of linewidths on photographic plates. The fitted band strengths lead to a well-defined electronic transition moment variation for the A – X system of ClO, which is in excellent agreement with an earlier determination by Mandelman and Nicholls from spectra at lower resolution (0.22 nm) with unresolved rotational structure.