The temperature and pressure dependence of the absorption cross-sections of NO2 in the 250-800 nm region measured by Fourier-transform spectroscopy

The absorption cross-sections of NO2 at atmospheric temperatures (223-293 K) and pressures (100 and 1000 mbar) were measured in the 250-800 nm (12500-40000 cm(-1)) region using Fourier-transform spectroscopy, at spectral resolutions of 0.5 cm(-1) above 435 nm and 1.0 cm(-1) below 435 nm (corresponding to about 8 and 16 pm at this wavelength). The wavenumber accuracy of the new cross-sections is better than 0.1 cm(-1) (about 0.5 pm at 250 nm and about 6.4 pm at 800 nm), validated by recording of I-2 absorption spectra in the visible using the same experimental set-up (light source, beam splitter, interferometer optics). The NO2 absorption spectra were recorded at five different sample temperatures between 223 and 293, K, and at each temperature at two total pressures (100 and 1000 mbar) using pure N-2 as buffer gas. Despite the weakness of this effect compared to the density of the NO2 absorption structures, pressure-broadening was clearly observed at all temperatures. The pressure-broadening was partially modeled using a convolution of the low-pressure NO2 absorption spectra with a Lorentzian lineshape. The pressure-broadening coefficient increases significantly with decreasing temperature, as already observed in the mid- and near-infrared vibration-rotation spectra of NO2. This effect is of importance for high-resolution spectroscopy of the earth's atmosphere in the UV-visible region. (C) 2002 Elsevier Science B.V. All rights reserved.