Linda R. Brown

Line positions and strengths of methane in the 2862 to 3000 cm−1 region☆

Abstract Measurements of line center positions and strengths of 1591 absorptions of CH 4 in the 2862 to 3000 cm −1 region have been made at high resolution. New assignments have been determined for several components in the P 14 and P 15 manifolds of the ν 3 band of 12 CH 4 . The strength data of the allowed transitions in the ν 3 band have been analyzed to determine the band strength and the coefficients of the F factor. The strength data given by Pine (1976) were also included in the analysis. For the ν 3 band, a strength of 259.5 cm −2 atm −1 at 296 K was obtained. Many forbidden lines in the ν 3 band were also observed in the spectra Line strengths in the ν 3 band of 13 CH 4 were determined from the spectra. The quantum assignments for the majority of the observed absorptions were not determined. These absorptions arise primarily from the bands 2 ν 2 , ν 2 + ν 4 , ν 2 + ν 3 − ν 2 and ν 3 + ν 4 − ν 4 for which there is presently little or no information.

Line intensities of methane in the 2700–2862-cm−1 region☆

Abstract Individual strengths and wavenumbers of 2080 methane absorption lines have been measured between 2700 and 2862 cm−1 at an average resolution of 0.023 cm−1 using a grating spectrometer. The results include all lines with strengths greater than 3 × 10−5 cm−2 atm−1 observable at 296 K with a maximum path of 32 m and a pressure of 4 Torr.

Line intensities of CO2 in the 2·7 micron region ☆

Individual line intensities have been measured at 0·025 cm−1 resolution and low pressures for the two strong Σ-Σ bands of C12O216 near 2.7 microns, as well as for their associated Π-Π hot-bands. Values of the rotationless dipole-moment matrix elements and vibration-rotation interaction coefficients are reported along with total band intensities. Results for the latter in cm−2 atm−1 at 296°K are: 25·7, 1·96, 39·3 and 3·23 for the 0201-0000, 0311-0110, 1001-0000, and 1111-0110 bands, respectively.

FT-IR measurements of cold cross sections of benzene (C6H6) for CASSINI/CIRS

Titan’s stratosphere is abundant in hydrocarbons (CxHy) producing highly complicated and crowded features in the spectra of Cassini/CIRS. Among these, benzene (C6H6) is the heaviest hydrocarbon ever seen in the Titan and cold planets. For this reason, a series of pure and N2-broadened C6H6 spectra were recorded in the 640 to 1540 cm−1region at gas temperatures down to 231 K using a Fourier transform spectrometer (Bruker IFS-125HR) at the Jet Propulsion Laboratory. We report temperature dependent absorption cross sections for three strong fundamental bands (ν4, ν14, ν13). We also derived pseudo-line parameters, which include mean intensities and effective lower state energies on a 0.005 cm−1frequency grid, obtained by fitting all the laboratory spectra simultaneously. For the pseudoline generation, details can be found in a JPL MK-IV website, http://mark4sun.jpl.nasa.gov/data/spec/Pseudo). The resulting pseudolines of the strong bands reproduce observed cross sections to within ̃3 %. These new results are compared to earlier work, including the C6H6+N2 spectra recorded at PNNL.a b

PERFORMANCE OF A CRYOGENIC MULTIPATH HERRIOTT CELL VACUUM-COUPLED TO A BRUKER IFS-125HR SYSTEM

Accurate modeling of atmospheric trace gases requires detailed knowledge of spectroscopic line parameters at temperatures and pressures relevant to the atmospheric layers where the spectroscopic signatures form. Pressure-broadened line shapes, frequency shifts, and their temperature dependences, are critical spectroscopic parameters that limit the accuracy of state-of-the-art atmospheric remote sensing. In order to provide temperature dependent parameters from controlled laboratory experiments, a 20.946 ± 0.001 m long path Herriott cell and associated transfer optics were designed and fabricated at Connecticut College to operate in the near infrared using a Bruker 125 HR Fourier transform spectrometer. The cell body and gold coated mirrors are fabricated with Oxygen-Free High Conductivity (OFHC) copper. Transfer optics are throughput matched for entrance apertures smaller than 2 mm. A closed-cycle Helium refrigerator cools the cell and cryopumps the surrounding vacuum box. This new system and its transfer optics are fully evacuated to ̃ 10 mTorr (similar to the pressure inside the interferometer). Over a period of several months, this system has maintained extremely good stability in recording spectra at gas sample temperatures between 75 and 250 K. The absorption path length and cell temperatures are validated using CO spectra. The characterization of the Herriott cell is described along with its performance and future applications.a b