A LOW-TEMPERATURE ABSORPTION CELL FOR FTS AND DIODE LASER SPECTROSCOPY OF GASES
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Date
1986
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Ohio State University
Abstract
Laboratory spectroscopy of gases at reduced temperatures provides a means for simplifying complex spectra, narrowing doppler widths, assigning energy levels, and measuring line strengths and broadenings as functions of temperature. We have constructed a cell which can be operated at any temperature between 50 and 300 Kelvin. The cell has a 30-cm path with a 2.5-cm bore to permit multiple passing of a small laser beam. A unique feature of this design is that the windows are sealed to the cell with spring-loaded teflon o-rings, which have proven to maintain a good seal down to 50 Kelvin. The cell is cooled with a single-stage closed-cycle helium refrigerator and the cell is continuously variable in temperature. The use of a refrigerator allows unattended operation for indefinite periods of time. The cell has been used to obtain spectra between 95 and 220 Kelvin with our diode laser spectrometer and with the l-m FTS at Kitt Peak.
Description
[FIGURE] (A) The $^{R}Q_{0}$ region in the 12-micron band of ethane, recorded with a sample temperature of 95 Kelvin. The linewidth is $0.0017 cm^{-1}$ FWHM. (B) The same spectrum as (A) deconvolved to remove the doppler lineshape. The resulting linewidth is $0.0006 cm^{-1}$ FWHM. Adress of authors: Planetary Systems Branch. Code 693.2. NASA Goddard Space Flight Center. Greenbelt, MD 20771.
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