Self-, N₂-, O₂-broadening coefficients and line parameters of HFC-32 for ν₇ band and ground state transitions from infrared and microwave spectroscopy

Abstract

Hydrofluorocarbons have been used as replacement gases of chlorofluorocarbons, since the latter have been phased out by the Montreal Protocol due to their environmental hazardous ozone-depleting effects. This is also the case of difluoromethane (CH₂F₂, HFC-32), which nowadays is widely used in refrigerant mixtures together with CF₃CH₃, CF₃CH₂F, and CF₃CHF₂. Due to its commercial use, in the last years, the atmospheric concentration of HFC-32 has increased significantly. However, this molecule presents strong absorptions within the 8–12 μm atmospheric window, and hence it is a greenhouse gas which contributes to global warming. Although over the years several experimental and theoretical investigations dealt with the spectroscopic properties of CH₂F₂, up to now pressure broadening coefficients have never been determined. In the present work, the line-by-line parameters of CH₂F₂ are retrieved for either ground state or ν₇ band transitions by means of microwave (MW) and infrared (IR) absorption spectroscopy, respectively. In particular, laboratory experiments are carried out on 9 pure rotational transitions of the ground state and 26 ro-vibrational transitions belonging to the ν₇ band lying around 8.2 μm within the atmospheric region. Measurements are carried out at room temperature on self-perturbed CH₂F₂ as well as on CH₂F₂ perturbed by N₂ and O₂. The line shape analysis leads to the first determination of self-, N₂-, O₂-, and air-broadening coefficients, and also of line intensities (IR). Upon comparison, broadening coefficients of ground state transitions are larger than those of the ν₇ band, and no clear dependence on the rotational quantum numbers can be reported. The obtained results represent basic information for the atmospheric modelling of this compound as well as for remote sensing applications.

Keywords:

• difluoromethane
• broadening coefficients
• spectroscopic line parameters
• N₂-, O₂-, air-broadening
• collisional cross sections

Acknowledgements

Cristina Puzzarini gratefully thanks Prof. G. Cazzoli for fruitful discussions. Nicola Tasinato thanks University Ca’ Foscari Venezia for his postdoctoral position.

Additional information

Funding

This work has been supported by Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR) (PRIN 2009 funds for project: ‘Molecular Spectroscopy for Atmospherical and Astrochemical Research: Experiment, Theory and Applications’), by University of Bologna (RFO funds) and by University Ca’ Foscari Venezia (FRA funds) [prot. no. 2009882CB8].