N$_2$ COLLISIONAL BROADENING OF METHANE IN THE THZ REGION MEASURED AT THE SOLEIL SYNCHROTRON

Abstract

Recently, we recorded the THz centrifugal distortion-induced spectrum of methane using synchrotron radiation at the SOLEIL facility. Intensities of pure rotation lines of CH$_4$ were precisely measured, from which the induced dipole moment of this weak spectrum, of great interest for planetology, was accurately inferred., in press (2010)} This study should in particular help to measure methane concentrations in Titan's atmosphere., {\em Icarus\/} {\bf 189}, 35--62 (2007).} Here, we continue the work by presenting spectra of CH$_4$/N$_2$ mixtures, again recorded with a 150 m optical path in a White cell and a Bruker IFS 125 HR FTIR spectrometer at the AILES beamline of SOLEIL. More precisely, the spectra were recorded with 5 \% of CH$_4$ in N$_2$ at various total pressures ({\it ca.\/} 100, 200, 400, 600 and 800 mbar). These spectra will allow to measure collisional broadening and shift coefficients, as well as line-mixing parameters, with N$_2$ as a perturber (like in Titan's atmosphere).