Line shape parameters of helium-broadened 12C16O transitions in the 3 → 0 overtone band near 1.57 µm

Abstract

Frequency-stabilized cavity ring-down spectroscopy was used to determine helium-broadened 12C16O line shape parameters for eleven lines in the 3 → 0 vibrational overtone band, including helium pressure broadening and pressure shifting. The spectra provided evidence of two non-Voigt mechanisms affecting line shape: collisional (Dicke) narrowing and speed dependence of the line broadening. Multispectrum fits of the speed dependent Nelkin-Ghatak profile (with the quadratic approximation for speed dependence) enabled precise determinations of the line shape parameters associated with these two mechanisms. The measured line shape parameters are presented and are compared to past work for helium-broadened 12C16O transitions in the 3 → 0 vibrational band (broadening coefficients) and in the 1 → 0 fundamental vibrational band (broadening and shifting coefficients). Significant reductions in the uncertainty of the broadening coefficients are demonstrated, along with the first determinations of helium pressure shifting and narrowing parameters for this transition. Analysis of the spectra at elevated pressure reveals evidence of line mixing with fitted first-order line mixing parameters that are consistent with literature values.