Spectral line parameters including line shapes in the 2ν3 Q branch of 12CH4

Devi, V. M., D. C. Benner, K. Sung, L. R. Brown, T. J. Crawford, S. Yu, M. A. H. Smith, A. W. Mantz, V. Boudon, and S. Ismail (2016), Spectral line parameters including line shapes in the 2ν3 Q branch of 12CH4, J. Quant. Spectrosc. Radiat. Transfer, 177, 152-169, doi:10.1016/j.jqsrt.2015.12.009.

In this study, we report the first experimental measurements of spectral line shape parameters (self- and air-broadened Lorentz half-widths, pressure-shifts, and line mixing (via off-diagonal relaxation matrix elements) coefficients and their temperature dependences, where appropriate) for transitions in the 2ν3 Q branch manifolds, Q(11)–Q(1) of methane (12CH4), in the 5996.5–6007-cm-1 region. The analysis included 23 high-resolution, high signal-to-noise laboratory absorption spectra recorded with the Bruker IFS125HR Fourier transform spectrometer (FTS) at JPL. The experimental data were obtained using 12C-enriched 12CH4 and dilute mixtures of 12CH4 in dry air in the 130–296 K range using a room-temperature long path absorption cell and, two custom-built coolable cells. In the analysis, an interactive multispectrum fitting software was employed where all the 23 spectra (11 self-broadened and 12 air-broadened) were fit simultaneously. By carefully applying reasonable constraints to the parameters for severely blended lines, we were able to determine a self-consistent set of broadening, shift and line mixing (relaxation matrix coefficients) parameters for CH4–CH4 and CH4–air collisions. In the majority of cases, a quadratic speed dependence parameter common for all transitions in each Q(J) manifold was determined. However, temperature dependences of the Q branch line mixing parameter could not be determined from the present data. Since no other experimental line shape measurements have been reported for this Q-branch, the present results are compared to available values in the HITRAN2012 database.

PDF of Publication: 
Download from publisher's website.
Research Program: 
Upper Atmosphere Research Program (UARP)