Empirical line parameters of methane in the 1.63-1.48 μm transparency window by high sensitivity Cavity Ring Down Spectroscopy
Résumé
The positions and intensities of methane in the 1.58 μm transparency window have been measured by high sensitivity Cavity Ring Down Spectroscopy at room temperature. The achieved sensitivity allowed measuring intensities as small as 3 × 10 -29 cm/molecule i.e. three orders of magnitude smaller than the intensity cut off of the HITRAN line list of methane. The complete list contains a total of 16,149 transitions between 6165 and 6750 cm -1. Their intensity values vary over six orders of magnitude from 1.6 × 10 -29 to 2.5 × 10 -23 cm/molecule. Transitions due to CH 3D in "natural" abundance in our methane sample were identified using a new spectrum of CH 3D recorded separately with a Fourier Transform spectrometer. From simulations of the CH 3D and methane spectra at low resolution, the CH 3D isotopologue has be found to contribute by up to 30% of the absorption near 1.58 μm.