Laboratory infrared spectroscopy of some important atmospheric trace gases.

摘要

High-resolution measurements of the infrared spectra of water vapor (H ₂O) carbon monoxide (CO) and the fluorocarbon C₂F₆ have been performed using a Bruker EFS-120 HR Fourier-transform spectrometer. Two stainless steel cryogenically cooled absorption cells have been employed with provided path lengths of 2.15 and 9.28 cm. A multiple-reflection White cell has also been used with path lengths between 3.2 to 41.2 meters in increasing steps of 3.2 meters. In order to retrieve the spectral line parameters from the observed transmission spectra, a multi-spectral non-linear least-squares fitting algorithm has been developed with special attention paid to the shape of the instrumental function of the spectrometer.; Spectral line parameters have been obtained for more than 1000 transmissions of water vapor in the 950–2100 Cm−1 and 3000–4050 Cm−1 regions. The measurements have been performed at 252, 273 and 296 K. Line positions, line strengths, self-broadened line widths and self-induced line shifts have been measured for all of these lines. Air-broadened line widths and air-induced line shifts have been obtained for some of the lines. The exponent n in the power law characterizing the dependence of air-broadened line widths upon temperature has been determined for the strong lines in these spectral regions mentioned.; Spectral line parameters have also been measured for the lines of 12C16O in the fundamental band and in the first overtone band. More than 100 spectra have been taken at several temperatures between 170 and 296 K to determine these parameters. Line strengths, self- and air-broadened line widths, self- and air-induced line shifts have been retrieved for the lines between P(24) and R(23) in the first overtone band. Line strengths, air-broadened line widths and air-induced line shifts have been retrieved for the spectral lines between P(23) and R(25) in the fundamental band. The exponent n characterizing the temperature-dependence of the self- and air-broadened line widths has been determined for the lines in both bands. Assuming a similar power law relationship, the temperature-dependence of the self- and air-induced line shifts, an exponent Π, has also been determined.; The absorption cross-sections have been measured for C₂F ₆ under the conditions appropriate to the terrestrial atmosphere, with temperatures in the range of 180 to 296 K, and the broadening pressures in the range of 30 to 760 torr. The measured band strengths (in units of 10 −16 cm-molecule−1) of the 8.0 and 8.95 μm bands are 1.636 ± 0.003 and 0.467 ± 0.0018, respectively.; The highly accurate spectroscopic parameters obtained in this work, many of which have not been reported previously, can be applied to the remote sensing and radiative transfer modeling of the terrestrial atmosphere. The data are also compared with the results in the literature reported by other investigators.