Room-temperature broadening and pressure-shift coefficients in the ν2 band of CH3D–O2: Measurements and semi-classical calculations


Predoi-Cross A, Hambrook K, Brawley-Tremblay S, Bouanich J-P, Devi MV, Smith MAH. Room-temperature broadening and pressure-shift coefficients in the ν2 band of CH3D–O2: Measurements and semi-classical calculations. Journal of Molecular Spectroscopy. 2006;236:75-90.


We report measured Lorentz O2-broadening and O2-induced pressure-shift coefficients of CH3D in the m2 fundamental band. Using amultispectrum fitting technique we have analyzed 11 laboratory absorption spectra recorded at 0.011 cm 1 resolution using theMcMath–Pierce Fourier transform spectrometer, Kitt Peak, Arizona. Two absorption cells with path lengths of 10.2 and 25 cm wereused to record the spectra. The total sample pressures ranged from 0.98 to 339.85 Torr with CH3D volume mixing ratios of 0.012 inoxygen. We report measurements for O2 pressure-broadening coefficients of 320 m2 transitions with quantum numbers as high asJ00 = 17 and K = 14, where K00 = K0 ” K (for a parallel band). The measured O2-broadening coefficients range from 0.0153 to0.0645 cm 1 atm 1 at 296 K. All the measured pressure-shifts are negative. The reported O2-induced pressure-shift coefficients vary fromabout 0.0017 to 0.0068 cm 1 atm 1. We have examined the dependence of the measured broadening and shift parameters on the J00,and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = J00, J00,and J00 + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadeningcoefficients to within 4.4%. The O2-broadening and pressure shift coefficients were calculated on the basis of a semiclassical modelof interacting linear molecules performed by considering in addition to the electrostatic contributions the atom–atom Lennard-Jonespotential. The theoretical results of the broadening coefficients are generally larger than the experimental data. Using for the trajectorymodel an isotropic Lennard-Jones potential derived from molecular parameters instead of the spherical average of the atom–atom model,a better agreement is obtained with these data, especially for |m| 6 12 values (11.3% for the first calculation and 8.1% for the secondcalculation). The O2-pressure shifts whose vibrational contribution are either derived from parameters fitted in the QQ-branch of selfinducedshifts of CH3D or those obtained from pressure shifts induced by Xe in the m3 band of CH3D are in reasonable agreement withthe scattered experimental data (17.0% for the first calculation and 18.7% for the second calculation). 2005 Elsevier Inc. All rights reserved.