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Abstract: New absorption cells designed specifically to achieve stable temperatures down to 66K inside the sample compartment of an evacuated Bruker IFS-125HR Fourier transform spectrometer (FTS) were developed at Connecticut College and tested at the Jet Propulsion Laboratory (JPL). The temperature stabilized cryogenic cells with path lengths of 24.29 and 20.38cm were constructed of oxygen free high conductivity (OFHC) copper and fitted with wedged ZnSe windows using vacuum tight indium seals. In operation, the temperature-controlled cooling by a closed-cycle helium refrigerator achieved stability of ±0.01K. The unwanted absorption features arising from cryodeposits on the cell windows at low temperatures were eliminated by building an internal vacuum shroud box around the cell which significantly minimized the growth of cryodeposits. The effects of vibrations from the closed-cycle helium refrigerator on the FTS spectra were characterized. Using this set up, several high-resolution spectra of methane isotopologues broadened with nitrogen were recorded in the 1200–1800cm−1 spectral region at various sample temperatures between 79.5 and 296K. Such data are needed to characterize the temperature dependence of spectral line shapes at low temperatures for remote sensing of outer planets and their moons. Initial analysis of a limited number of spectra in the region of the R(2) manifold of the ν 4 fundamental band of 13CH4 indicated that an empirical power law used for the temperature dependence of the N2-broadened line widths would fail to fit the observed data in the entire temperature range from 80 to 296K; instead, it follows a temperature-dependence similar to that reported by Mondelain et al. . The initial test was very successful proving that a high precision Fourier transform spectrometer with a completely evacuated optical path can be configured for spectroscopic studies at low temperatures relevant to the planetary atmospheres. [Copyright &y& Elsevier]

Abstract: We present measurements of He-broadening parameters for the R(0) and P(2) lines in the fundamental band of 13CO at different temperatures between 12K and room temperature. The broadening parameters are determined, taking into account confinement narrowing, by simultaneous least-squares fitting of spectra recorded using a frequency stabilized diode laser spectrometer. The pressure broadening cross sections are deduced and compared to close-coupling calculations and earlier results obtained for rotational transitions of 12CO. [Copyright &y& Elsevier]

We present measurements of Ar-broadening parameters for the R(0) and R(7) lines in the fundamental band of 13CO at eight temperatures from 80 to 297 K. The broadening parameters are determined by simultaneous least-squares fitting of spectra recorded using a frequency stabilized diode laser spectrometer. The comparison of the broadening parameter values for R(7) derived at room temperature and different pressures from different line profiles shows that an empirical line profile, which takes into account narrowing effects (Dicke narrowing and absorber speed dependence) but neglects any correlation between collisions, is able to describe the observed lines with constant values of the narrowing and broadening parameters over a 10–500 Torr pressure range. Starting from a recent ab initio potential energy surface, theoretical thermally averaged close coupling values of the Ar broadening parameter are calculated for the same temperatures. The comparison between experimental and calculated values shows an overall agreement of 1.5%. [Copyright &y& Elsevier]

Abstract: We report measurements of self- and nitrogen-pressure broadening of the P(11) line in the ν 1 + ν 3 combination band of acetylene at 195 739.649 5135(80)GHz by absorption of radiation emitted by an extended cavity diode laser referenced to a femtosecond frequency comb. Broadening, shift and narrowing parameters were determined at 296K. For the most appropriate, hard collision, model in units of cm−1/atm, we find 0.146317(27), 0.047271(104) and −0.0070819(22) for the acetylene self-broadening, narrowing and shift, and 0.081129(35), 0.022940(74) and −0.0088913(25) respectively, for the nitrogen-broadening parameters. The uncertainties are expressed as one standard deviation (in parenthesis) in units of the last digit reported. These parameters are 2–3 orders of magnitude more precise than those reported in previous measurements. Similar analyses of the experimental data using soft collision and simple Voigt lineshape models were made for comparison. [Copyright &y& Elsevier]

Room temperature values for self-broadened and hydrogen-broadened Lorentz halfwidth coefficients, and self and hydrogen pressure-induced shift coefficients have been measured for transitions with rotational quantum number m ranging between -24 and 24 in the 2 ← 0 band of 12C16O. The spectra were recorded with the McMath–Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak. The analysis was performed using a multispectrum nonlinear least squares technique. We have compared our results with similar measurements published recently. [Copyright &y& Elsevier]

We have analyzed the methyl fluoride RQ(J,0) Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines. [Copyright &y& Elsevier]