Absorption coefficients of ClONO2 at 780 cm−1

Abstract

The absorption coefficients of the Q branch of the ν4 band of ClONO2 at 780 cm−1 have been measured over a sample pressure range of 0.1 to 0.4 torr using a tuneable diode laser spectrometer. The peak absorption coefficients derived from these measurements are 1.98(42) × 10−18 cm2 mol−1 at 296K, and 2.98(47)× 10−18 cm2 mol−1 at 210K. These are in good agreement with those determined previously by Fourier transform spectroscopy once corrections for the resolution of the instruments are made. Band contour analysis of the ν4 + ν6 − ν6 and ν4 + 2ν9 − 2ν9 bands of 35ClONO2 has been carried out and the results incorporated in the fitting of the observed spectrum. At 213K the integrated intensity of the theoretical spectrum calculated for the range of identified bands is 6.4 × 10−18 cm−1 mol−1. The derived integrated intensity of this whole band system is 8.6 × 10−18 cm−1 mol−1, assuming all transition moments of the contributing bands are identical. For the 296K spectrum of the ν4 system a value of 3.9 × 10−18 cm−1 mol−1 is obtained, with a value of 8.4 × 10−18 cm−1 mol−1 if all populated states are included. The differences between the integrated intensities of the theoretical spectrum and of the band system are associated with the “continuum” contributed by the large number of weak bands associated with thermally populated states. The values obtained for the band systems may be compared with those derived by Ballard et al. [1988] over the range 750 to 830 cm−1 for the entire ν3/ν4 system, and by Davidson et al. [1987] over the range 750 to 791 cm−1. These were 2.09 × 10−17 cm−1 mol−1 at 213K and 3.04 × 10−17 cm−1 mol−1 at 296K for the entire ν3/ν4 system, and 8.1 × 10−18 cm−1 mol−1 at 223K and 12.9 × 10−18 cm−1 mol−1 at 296K.