Molecular line intensity and line shape, and their temperature dependence, are fundamental parameters to the understanding of planetary atmospheres and other problems with environmental implications. Fourier transform spectrometers and tunable diode lasers are frequently used to determine these parameters. An accurate understanding of the instrument line width is important to eliminate instrumental effects form the experimental data.
Low temperature absorption by molecular lines are characterized by narrow Doppler widths which can be of the same order of magnitude as the laser emission line widths. Measurements of low temperature gases under low pressure conditions may be used to study laser emission line shape. These low temperature conditions have also been used to investigate intramolecular collision potentials in the microwave spectral region using a technique referred to as collisional cooling; this experimental technique has been employed to study water vapor at temperatures of approximately 1 Kelvin. We have measured methyl fluoride gas at temperatures less than 10 Kelvin, and we have measured carbon monoxide gas to temperatures as low as 11 Kelvin.
Results of this work will be described.