Self- and N2-broadening of CH3Br ro-vibrational lines in the ν2 band: The J and K dependence

Methyl bromide (CH3Br) is the major source of inorganic bromine in the atmosphere and contributes significantly to ozone depletion. Indeed, CH3Br is dissociated by UV radiation, producing Br radicals that catalyze the destruction of ozone. In this paper, we report measured Lorentz self- and N-2-broadening coefficients of CH3Br in the nu(2) fundamental band using a mono-spectrum non-linear least squares fitting of Voigt profiles which appeared to properly model the observed molecular line shapes within the noise level. These measurements were made by analyzing 12 laboratory absorption spectra recorded at high resolution (0.005, 0.003 or 0.002 cm(-1)) using the Fourier transform spectrometer Bruker IF125HR located at the LISA facility in Creteil. The spectra were obtained at room temperature using a White-type multipass cell with an optical path of 0.849 m and various pressures. We have been able to determine the self- and N-2-broadening coefficients of 948 nu(2) transitions with quantum numbers as high as J = 49 and K = 10. The measured self-broadening coefficients range from 0.1542 to 0.4930 cm(-1) atm(-1) and the N-2-broadening coefficients range from 0.0737 to 0.1284 cm(-1) atm(-1) at 295 K. The accuracy of the broadening coefficients measured in this work is between 4% and 8%, depending on the studied transition. Comparisons with measurements taken in the nu(5) and nu(6) bands of CH3Br did not show any clear vibrational dependence. The J and K dependences of the self- and N-2-broadening coefficients have been observed and the rotational K dependence has been modeled using empirical polynomial expression. On average, the empirical expression reproduce the measured broadening coefficients to within 6%. The data obtained represent a significant contribution to the determination of broadening coefficients of CH3Br useful for atmospheric remote sensing and applications. (C) 2014 Elsevier Inc. All rights reserved.