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Cryogenic Absorption Cells Operating Inside a Bruker IFS-125HR: First Results for 13CH4 at 7 MicrometersNew absorption cells designed specifically to achieve stable temperatures down to 66 K 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 20.38 cm 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 0.01 K. 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 1200-1800 per centimeter spectral region at various sample temperatures between 79.5 and 296 K. 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 v4 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 296 K; instead, it follows a temperature-dependence similar to that reported by Mondelain et al. [17,18]. 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.
Document ID
20100042368
Acquisition Source
Langley Research Center
Document Type
Reprint (Version printed in journal)
Authors
Sung, K.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Mantz, A. W.
(Connecticut Coll. New London, CT, United States)
Smith, M. A. H.
(NASA Langley Research Center Hampton, VA, United States)
Brown, L. R.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Crawford, T. J.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Devi, V. M.
(College of William and Mary Williamsburg, VA, United States)
Benner, D. C.
(College of William and Mary Williamsburg, VA, United States)
Date Acquired
August 25, 2013
Publication Date
June 1, 2010
Publication Information
Publication: Journal of Molecular Spectroscopy
Publisher: ScienceDirect
Volume: 262
Issue: 2
Subject Category
Inorganic, Organic And Physical Chemistry
Report/Patent Number
NF1676L-11843
Funding Number(s)
WBS: WBS 811073.02.04.02.28
Distribution Limits
Public
Copyright
Other

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