Multispectrum analysis of 12CH4 in the ν4 band: I

Abstract:

Lorentz air-broadened half widths, pressure-induced shifts and their temperaturedependences have been measured for over 430 transitions (allowed and forbidden) inthe n4 band of 12CH4 over the temperature range 210–314K. A multispectrum non linearleast squares fitting technique was used to simultaneously fit a large number of high-resolution (0.006–0.01cm1) absorption spectra of pure methane and mixtures ofmethane diluted with dry air. Linemixing was detected for pairs of A-, E-, and F-speciestransitions in the P- and R-branch manifolds and quantified using the off-diagonalrelaxation matrix elements formalism. The measured parameters are compared toair- and N2-broadened values reported in the literature for the n4 and other bands. Thedependence of the various spectral line parameters upon the tetrahedral symmetryspecies and rotational quantum numbers of the transitions is discussed. All data used inthe present work were recorded using the McMath–Pierce Fourier transform spectro-meter located at the National Solar Observatory on Kitt Peak.Published by Elsevier Ltd.