H2 broadening in the ν3 and ν4 bands of CH4 at room temperature

Gharib-Nezhad, Ehsan

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https://hdl.handle.net/2142/100489 Copy

Description

Title

H2 broadening in the ν3 and ν4 bands of CH4 at room temperature

Author(s)

Gharib-Nezhad, Ehsan

Contributor(s)

• Bechtel, Hans A
• Stark, Glenn
• Line, Michael R.
• Lyons, James R.
• Heays, Alan

Issue Date

2018-06-18

Keyword(s)

Linelists, Lineshapes, Collisions

Abstract

Methane (CH4) is the dominant carbon-bearing molecule in terrestrial and exoplanetary atmospheres where the temperature is below 1000 K. Therefore, knowing its pressure-induced H2-broadened absorption cross section is fundamental for exoplanetary atmospheric modeling. In this study, the pressure-induced H2-broadening coefficients of CH4 are determined in the spectral regions 2800-3200 (ν3) and 1200-1400 cm−1 (ν4). The laboratory transmission spectra in this study were recorded at high resolution (i.e., 0.005 and 0.01 cm−1 ) at room temperature with an FTIR 125HR Bruker spectrometer at Lawrence Berkeley National Laboratory. The CH4 pressure was constant during the entire experiment (29 mtorr), and elevated H2 pressures were used in the range 100-700 torr. The Lorentzian coefficients are determined by a nonlinear regression approach in order to model the relationship between the linewidth and its corresponding pressure. Our preliminary results show that the Lorentzian coefficients of different lines in these two bands fall in the range 0.06-0.09 cm−1 /atm, consistent with the previous available measurements. Atmospheric modeling will be employed using exoplanet forward transmission modeling to highlight the importance of H2-broadening of CH4 to exoplanetary observations.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100489

DOI

10.15278/isms.2018.MI03

Copyright and License Information

Copyright 2018 Ehsan Gharib-Nezhad

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