Measurements of H2O line parameters and self-continuum in the spectral range 700 - 2000 cm-1 (v2 + atmospheric window)

Abstract

A Bruker IFS 125 HR Fourier transform interferometer in combination with a multireflection cell was used to measure pure water transmission spectra in the spectral range 700 - 2000 cm-1. Various spectra with absorption path lengths between 14 and 161 m, sample gas pressures from 0.003 to 20 mbar and temperatures between 278 and 350 K were recorded. The recorded spectra were corrected for detector non-linearity, thermal self-radiation and for deviations from an ideal instrumental line shape. A micro-window-based multispectrum-fitting-approach was used, applying a quadratic speed-dependent Voigt model which was extended to account for line mixing. Line positions, line intensities, self-shifts, self-broadening widths, their speed-dependence, temperature exponents, temperature shifts and in some cases line mixing were adjusted for fitting the corrected spectra. Continuum information was extracted from baselines, which were fitted simultaneously with monomer lines during the multispectrum fits. Continua were then obtained by a combined fit of all measurements containing significant continuum information. The self-continuum for room temperature was derived for the entire spectral range covered and is compared to measurements from other groups. The good quality of the self-continuum and the visibility of high-resolution features in the v2 in-band region allows for a comparison with dimer spectra. Results are presented for different temperatures.