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Monodeuterated methane (CH3D) is a constituent trace species in several planetary atmospheres, and its spectrum is often used in determinations of atmosphericH/Dratios. Methane plays an important role in terrestrial atmospheric chemistry. It is the most abundant hydrocarbon in our atmosphere and as anIRactive gas makes an important contribution to the enhanced greenhouse effect. Methane is increasing in the Earth’s atmosphere at a rate of about 1% per year. The current knowledge of its sources and sinks are not sufficient to isolate the cause of the observed changes in the mixing ratio and global distribution. As a result, the infrared spectrum of methane and its isotopomers is continually being investigated in order to obtain improved spectroscopic line parameters needed to interpret remote sensing observations. Remote sensing instruments require laboratory data sets based on measurements of very high accuracy. The primary objective of this study is to enhance our spectroscopic knowledge of monodeuterated methane in theν6band located at 6.8 microns. We present measurement results for self- and N2-broadened line parameters from room temperature down to about 80K. A total of 23 high-resolution, highS/Nspectra recorded with two Fourier transform spectrometers: a) the McMath-Pierce FTS located on Kitt Peak and b) a Bruker IFS-125HR FTS at the Jet Propulsion Laboratory (JPL)1were fit simultaneously in a multispectrum approach. 2The set included both pure CH3D and dilute mixtures of CH3D in research grade nitrogen. The variations in the measured line parameters with the symmetry species, the rotational quantum numbers and with temperature are reported and discussed in comparison with earlier measurements. For the case of nitrogen-broadening, we also provide semi-classical calculations based on a rigorous treatment of the active molecule as a symmetric top, a model intermolecular potential comprising both short- and long-range interactions, and exact classical trajectories. These calculations are done for various temperatures and for wide ranges of rotational quantum numbers. The role of the various high-order multipoles in the line-broadening at low, middle and high values of the rotational quantum numberJis investigated. Main features of theK-dependences are also analyzed. These theoretical values are included in the general comparison of our new experimental and already available in the literature results.3

Accurate knowledge of spectral line shape parameters is important for infrared transmission and radiance calculations in the terrestrial atmosphere. We report the self and air-broadened Lorentz widths, shifts and line mixing coefficients along with their temperature dependencies for methane absorption lines in the 2.2 µm spectral region. For this, we obtained a series of high-resolution, high S/N spectra of 99.99% 12C-enriched samples of pure methane and its dilute mixtures in dry air at cold temperatures down to 150 K using the Bruker IFS 125HR Fourier transform spectrometer at JPL. The coolable absorption cell had an optical path of 20.38 cm and was specially built to reside inside the sample compartment of the Bruker FTS1. The 13 spectra used in the analysis consisted of seven pure 12CH4 spectra at pressures from 4.5 to 169 Torr and six air-broadened spectra with total sample pressures of 113-300 Torr and methane volume mixing ratios between 4 and 9.7%. These 13 spectra were fit simultaneously using the multispectrum least-squares fitting technique2. The results will be compared to existing values reported in the literature3.

Spectral line parameters, including line center positions, absolute line intensities, self- and N2-broadened halfwidth coefficients, and the temperature dependences of these halfwidth coefficients, have been measured for more than 1330 transitions in the ν9 band of ethane (C2H6) by applying a multispectrum nonlinear least squares analysis technique.1 We analyzed a total of 43 high-resolution (0.00156-0.005 cm−1) infrared absorption spectra recorded with two different Bruker Fourier transform spectrometers (at PNNL and at JPL) at various sample path lengths, pressures and temperatures. The ν9 fundamental of C2H6 is the strongest band in the terrestrial spectral window, and it is often used for ethane identification and abundance determination in remote sensing of planetary atmospheres. Torsional splittings are fairly large (dependent upon J;K) and measurable in several rQ and pQ sub-band structures. However, in the case of the rQ0 sub-band the two split components are completely obscured because of the overlap of Doppler-broadened J transitions. The results from the present study2 will be compared with other published data.

This paper describes the status of the 2004 edition of the HITRAN molecular spectroscopic database. The HITRAN compilation consists of several components that serve as input for radiative transfer calculation codes: individual line parameters for the microwave through visible spectra of molecules in the gas phase; absorption cross-sections for molecules having dense spectral features, i.e., spectra in which the individual lines are unresolvable; individual line parameters and absorption cross-sections for bands in the ultra-violet; refractive indices of aerosols; tables and files of general properties associated with the database; and database management software. The line-by-line portion of the database contains spectroscopic parameters for 39 molecules including many of their isotopologues.The format of the section of the database on individual line parameters of HITRAN has undergone the most extensive enhancement in almost two decades. It now lists the Einstein A-coefficients, statistical weights of the upper and lower levels of the transitions, a better system for the representation of quantum identifications, and enhanced referencing and uncertainty codes. In addition, there is a provision for making corrections to the broadening of line transitions due to line mixing. (C) 2005 Elsevier Ltd. All rights reserved.