Water-vapor continuum CO_2 laser absorption spectra between 27°C and −10°C

Abstract

Water continuum CO2 laser absorption spectra are reported for temperatures between 27 and -10 degrees C. The continuum is found to possess a negative temperature coefficient. The results obtained suggest that the magnitude of this temperature coefficient increases with increasing water pressure and decreasing temperature. The temperature coefficients between 27 and 10 degrees C for air mixtures containing 3.0- and 7.5-Torr water vapor are -2.0 +/- 0.4 and -2.9 +/- 0.5%/ degrees C, respectively. For mixtures with 3.0-Torr water the 10-0 degrees C temperature coefficient is -7.7 +/- 0.2%/degrees C. The temperature and water pressure dependencies observed for the continuum suggest that while both collisional broadening and water dimer mechanisms contribute to the continuum, the dimer mechanism is more important over this temperature range.

The water vapour self- and water–nitrogen continuum absorption in the 1000 and 2500 cm −1 atmospheric windows

“…In the majority of laboratory measurements of the water-nitrogen continuum in the 1000 cm −1 window, a tunable CO 2 -laser was used as a radiation source, and the P(20) transition at 944.2 cm −1 was the most popular in those investigations. It can be seen from the figure that the measurements of Nordstrom et al [18], Loper et al [20] and Cormier et al [15] agree with each other and provide the foreign continuum value of about 6 × 10…”

“…These authors reported measurements with both a long path cell and spectrophone techniques at 26 CO 2 -laser transitions. Some of the results seem to have significant local line contribution to the absorption, as it is in the case of measurement on the R (20) 975.93 and R(14) 971.93 cm −1 transitions (see table 1 from Peterson et al [19]). In some other cases, the water vapour continuum absorption coefficients obtained with the opto-acoustic detector significantly deviate from measurements with the multi-pass cell.…”

“…Our experimental data on the water-nitrogen continuum in the 800-1230 cm −1 spectral range (solid thin line and black circles with error bars) in comparison with the models and with the data from other sources. Crosses: McCoy et al [17], (cell, 298 K); open diamonds: Nordstrom et al [18], (cell, 296 K); black squares: Peterson et al [19], (cell, 298 K); grey squares: Peterson et al [19] (spectrophone, 298 K); grey diamonds: Loper et al [20], (spectrophone, 296 K); open circles: Hinderling et al [21], (spectrophone, 298 K); grey triangles: Cormier et al [15], (CRDS, 326 K); grey circles with error bars: Burch & Alt [22], (cell, 296 K).…”

Theory of the water vapor continuum and validations

“…In Fig. 12, we show a comparison for the temperature dependence of the self absorption coefficient at frequencies near 1203 cm~' with experimental data obtained by a number of researchers using different experimental techniques (Burch et al, 1971;Montgomery, 1978;Loper et al, 1983). Also shown are some data from Varanasi (1988b) for a frequency near 1000 cm~'.…”

“…Roberts et al (1976) derived an analytic expression for the continuum in the 8-13 /im region by fitting the data of Burch et al (1971Burch et al ( , 1974Burch et al ( , 1975. This formulation is still widely used because of its simplicity, but it does not reproduce the improved experimental laboratory data of Burch and co-workers (1982Burch and co-workers ( , 1984Burch and co-workers ( , 1985, nor does it model correctly the temperature dependence observed by Montgomery (1978) and by Loper et al (1983). Thomas and Nordstrom (1980, 1982a,b, 1985 sought to model the continuum absorption in terms of a modified line shape.…”