Measurements of H2O-N2 line shape parameters and the determination of the intermolecular potential for complex Robert-Bonamy-Ma calculations

Abstract

Ten sets of N₂-mixture spectra of H₂O were measured for the ν₂ and 2ν₂-ν₂ bands in the 1200–1950 cm^-1 region at room temperature using a straight-pass glass gas cell with KCl windows housed in the Bruker 125HR high-resolution Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory (JPL). The spectra were fit simultaneously using a multispectrum fitting software, which adopts a speed-dependent Voigt line shape profile having full line mixing effects taken into account through a relaxation matrix operation. N₂-broadened half-width and N₂-induced frequency shift coefficients were determined for 395 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 166 transitions with less than 3 % difference were chosen. Additional filtering was done using the air-broadened data of Birk and Wagner [JQSRT 2012;113, 889–928] and the H₂OO₂ CRBM calculations of Gamache et al. [Mol. Phys. 2024;122: e2281592] to form air-broadening values for the measurements made here. The air-broadened values that agree with the Birk and Wagner data better than 3.0 % were retained. The list was augmented with 57 measurements that have γ less than 0.05 cm^-1 and the pairing rules applied again. The final list contains 150 transitions. Using these data, Complex Robert-Bonamy-Ma calculations were made to determine the intermolecular potential for the H₂ON₂ collision system. Starting from the potential of Vispoel et al. [JQSRT 2019;228:79]. potential parameters were changed iteratively until a final potential (potential RG23) was determined. The final results agree with the selected half-width measurements having an average difference of -1.67 %, an average absolute difference of 3.87 % and a standard deviation of 5.45 %. Calculations were then made for all ν₂ transitions in the measurement database [Gamache and Hartmann, Can J Chem 2004;82:1013] to check the final intermolecular potential.