Measurements and theoretical calculations of self-broadening and self-shift coefficients in the ν2 band of CH3D


Predoi-Cross A, Hambrook K, Brawley-Tremblay M, Bouanich J-P, Malathy Devi V, Benner CD, Brown LR. Measurements and theoretical calculations of self-broadening and self-shift coefficients in the ν2 band of CH3D. Journal of Molecular Spectroscopy. 2005;234:53-74.


In this paper, we report measured Lorentz self-broadening and self-induced pressure-shift coefficients of 12CH3Dinthe m2 fun-damental band (m0  2200 cm1). The multispectrum fitting technique allowed us to analyze simultaneously seven self-broadenedabsorption spectra. All spectra were recorded at the McMath-Pierce Fourier transform spectrometer of the National Solar Obser-vatory (NSO) on Kitt Peak, AZ with an unapodized resolution of 0.0056 cm1. Low-pressure (0.98–2.95 Torr) as well as high-pres-sure (17.5–303 Torr) spectra of 12C-enriched CH3D were recorded at room temperature to determine the pressure-broadeningcoefficients of 408 m2 transitions with quantum numbers as high as J00 = 21 and K = 18, where K00 = K0 ” K (for a parallel band).The measured self-broadening coefficients range from 0.0349 to 0.0896 cm1 atm1 at 296 K. All the measured pressure-shiftsare negative. The reported pressure-induced self-shift coefficients vary from about 0.004 to 0.008 cm1 atm1.We have examinedthe dependence of the measured broadening and shift parameters on the J00, and K quantum numbers and also developed empiricalexpressions to describe the broadening coefficients in terms of m (m = J00, J00, and J00 + 1 in the QP-, QQ-, and QR-branch, respec-tively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 3.6%. A semiclassicaltheory based upon the Robert–Bonamy formalism of interacting linear molecules has been used to calculate these self-broadeningand self-induced pressure-shift coefficients. In addition to the electrostatic interactions involving the octopole and hexadecapolemoments of CH3D, the intermolecular potential includes also an atom–atom Lennard–Jones model. For low K (K 6 3) with|m| 6 8 the theoretical results of the broadening coefficients are in overall good agreement (3.0%) with the experimental data.For transitions with K approaching |m|, they are generally significantly underestimated (8.8%). The theoretical self-induced pressureshifts, whose vibrational contribution is derived from results in the QQ-branch, are generally smaller in magnitude than the exper-imental data in the QP-, and QR-branches (15.2%). 2005 Elsevier Inc. All rights reserved.