Measurements of H₂O-O₂ line shape parameters and the determination of the intermolecular potential for modified complex Robert-Bonamy calculations

A series of spectra, one pure H₂O and four H₂O-O₂ mixtures, were measured for the ν₂ band in the 1200–1950 cm⁻¹ region at room temperature using a single-pass copper cell housed in the Bruker 125HR high-resolution Fourier transform spectrometer (FTS) at Jet Propulsion Laboratory (JPL). All the five spectra were fit simultaneously using a multispectrum non-linear least-squares fitting software, Labfit programme suite, which adopts a speed-dependent Voigt line shape profile using full line mixing taken into account through a relaxation matrix operation. O₂-broadened half-width and O₂-induced frequency shift coefficients were determined for more than 350 transitions of H₂¹⁶O. These data were then checked using the smooth variation and paring rules [Brown et al. J Mol Spectrosc. 2007;246:1-21, Ma et al. Mol Phys. 2011;109:1925-41] and 186 transitions that obey the rules with less than 3% difference were chosen. Using these selected data, Modified Complex Robert-Bonamy calculations were made to determine the intermolecular potential for the H₂O-O₂ collision system. Some 93 potential were investigated resulting in a final potential (potential 74) that agrees with the selected half-width measurements having an average percent difference of 0.052 and a standard deviation of 5.108% between measurement and calculations.