Empirical line parameters of methane in the 1.63–1.48μm transparency window by high sensitivity Cavity Ring Down Spectroscopy

Abstract

We have completed the spectral coverage of the 1.58 m transparency window of methane by high sensitivity Cavity Ring Down Spectroscopy at room temperature. The achieved sensitivity ( min~3 10-10 cm-1) allowed measuring line intensities as weak 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 16223 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. By comparison with a spectrum of CH 3 D recorded separately by Fourier Transform Spectroscopy, transitions due to CH 3 D in "natural" abundance in our methane sample were identified. The relative contribution of the CH 3 D isotopologue estimated by simulation of the CH 3 D and methane spectra at low resolution has showed that the CH 3 D absorption may contribute to the absorption in the region by up to 30%.

The near-IR spectrum of Titan modeled with an improved methane line list

“…This leaves two small regions (6181 -6289 and 6526 -6717 cm -1 ) where no low temperature measurements are available. In these regions we used room temperature measurements by Campargue et al (2010b). Some lines in these regions were assigned lower state energies based on quantum identifications by Nikitin et al (2010b).…”

“…This indicates that the line widths in a typical H 2 /He giant planet atmosphere should be little different to those in air, and our line list should be useable for such atmospheres without any correction. A particular advantage of the new list is that it includes many more weak lines in the 1.6 µm transparency region due to the new CRDS data from Campargue et al (2010b) and Wang et al (2010b). In this region HITRAN 2008 has an intensity limit of 3.7 × 10 -26 cm mol -1 and this is not deep enough to include a significant number of methane lines, but it is at these wavelengths where we see the most flux from Titan.…”

Accurate measurements of line strengths and air-broadening coefficients in methane around 1.66 µm using cavity ring down spectroscopy

“…It is interesting to compare the results on methane line intensities obtained in this work, with recent other experimental studies on methane in this wavelength region. During the last 10 years the group of Campargue in Grenoble performed a detailed, accurate study on methane between 1.26 and 1.71 μm [30][31][32][33][34][35][36][37][38] . The values of the line parameters, such as frequency and intensity, were determined using two spectroscopic techniques: Cavity Ring Down Spectroscopy and Differential Absorption Spectroscopy.…”

“…Next to theoretical studies numerous laboratory measurements were performed of methane line parameters in different spectral regions. For the measurements of line positions and intensities different spectroscopic techniques were used: Fourier Transform Spectroscopy [22][23][24][25][26][27][28][29] , Differential Absorption Spectroscopy [25,[30][31][32][33] , cavity ring down spectroscopy [34][35][36][37][38] , Dual Comb Spectroscopy [39] , highintensity Synchrotron radiation combined with Fourier Transform Spectroscopy [40] , Intracavity Laser Spectroscopy [41] . In recent years many studies were carried out, devoted to line shape analysis and determination of line parameters such as broadening coefficients, line shifts and line mixing parameters [e.g.…”

Modelling the near-infrared spectra of Jupiter using line-by-line methods

“…We have not attempted to model wavelengths shorter than 1.6 μm. However, new empirical methane line data for these wavelength regions are starting to become available (Sciamma‐O'Brien et al 2009; Campargue et al 2010a,b), which may enable our modelling to be extended to shorter wavelengths.…”