Line mixing calculation in the ν6 Q-branches of N2-broadened CH3Br at low temperatures

Abstract

Abstract:In an early study [Tran H, Jacquemart D, Mandin JY, Lacome N, JQSRT 2008;109:119-31], line mixing effects of the  6 band of methyl bromide were observed and modeled at room temperature. In the present work, line mixing effects have been considered at low temperatures using state-to-state collisional rates which were modeled by a fitting law based on the energy gap and a few fitting parameters. To validate the model, several spectra of methyl bromide perturbed by nitrogen have been recorded at various temperatures (205-299K) and pressures . Comparisons between measured spectra and calculations using both direct calculation from relaxation operator and Rosenkranz profile have been performed showing improvement compared to the usual Lorentz profile. Note that the temperature dependence of the spectroscopic parameters has been taken into account using results of previous studies.

The 2009 edition of the GEISA spectroscopic database

“…In the absence of experimental or theoretical results for air-pressure shifts for CH 3 Br, the GEISA standard missing value of À 9.999999 cm À 1 atm À 1 has been used for all transitions. Note also that line mixing effects have been observed and modeled in the strong Q-branches between 220 and 300 K [375,376]. Line mixing parameters (for direct calculation or Rosenkranz profile [377]) are available upon request to the authors.…”

Recent advances in collisional effects on spectra of molecular gases and their practical consequences

“…Considering the state-to-state rates, they are often modeled using energy-gap fitting laws (IV.3.2 of [1] and [327]) based on a few parameters that are generally deduced from fits of line-broadening data. New applications of this type of approach to LM effects for a variety of molecules can be found in [238,245,272,[304][305][306][307][308]315,[328][329][330][331][332]. Note that there is a rarely used alternative solution.…”

High resolution synchrotron far-infrared study of CH2D79Br: The v6 fundamental and 2v6−v6, v5+v6−v6 and v6+v9−v6 hot bands

“…It is classified as one of the most ozone-depleting substances since it is readily photolyzed to form elemental bromine in the stratosphere which is destructive to the Earth's ozone layer [3]. Highly accurate infrared spectroscopic data ( [4] and references therein) are therefore crucial to model the opacity of this compound in the atmosphere. Analogous studies on its isotopic varieties are also of importance for refining the molecular potential energy surface of this molecule.…”