Pressure-broadening of water transitions near 7180 cm−1 by helium isotopes

In this study, pressure-broadening parameters for several H2O transitions near 7180 cm−1 are obtained which describe collisions with 3He and 4He. The sensitivity of those parameters to choice of theoretical line profile (Galatry vs. Voigt) is investigated. H2O is an important species in atmospheric chemistry and astronomy. Because of this, basic fundamental research, which explores the nature of the H2O spectrum in the presence of different gases of varying physical properties, can provide useful reference data which can be applied in the fields of atmospheric and planetary remote sensing. Measurements were made using an intensity-modulated laser photoacoustic spectrometer. Results from the present work show that Galatry line profiles, with a constrained narrowing parameter, more accurately describe experimental spectra than Voigt profiles over a wide range of experimental pressure conditions. Average pressure-broadening parameters were found to be 0.0216 cm−1/atm and 0.0209 cm−1/atm for H2O in 3He and 4He, respectively, and were compared to a literature model for the mass-dependence of line broadening. Specific values were obtained for each transition with nominal combined uncertainties of 2–6%.

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► We measure pressure-broadening parameters for H2O in 3He and 4He near 7180 cm−1.
► We find that Galatry profiles more accurately represent data than Voigt profiles do.
► We find that 3He is a more efficient foreign broadener than 4He by ≈4%.