Air-broadened linewidth measurements in the ν₂ vibrational band of HOCl

Abstract

Infrared rotational line-broadening coefficients in air are one of the parameters required to determine absolute trace gas concentrations from high-resolution absorption spectra. Air-broadening coefficients have been measured for two infrared absorption lines of the ν₂ band of HO³⁵Cl; the 8_1,7←7_1,6 and 14_1,14←13_1,13 lines at 1247.3169 and 1252.8437 cm⁻¹, respectively. We obtain values of 0.112 cm⁻¹ atm⁻¹ [half-width half-maximum (HWHM)] for the J″ = 7 line and 0.0955 cm⁻¹ atm⁻¹ (HWHM) for the J″ = 13 line. These measurements were made over the pressure range 2–200 Torr (760 Torr atm⁻¹) using a high-resolution tunable diode laser system with an optical pathlength of 100 m. The results of these measurements are essential for the implementation of such an instrument to measure HOCl in the lower atmosphere.