Abstract

The so-called line-by-line procedure is an impractical procedure in the case of several chlorofluorocarbons (CFCs). Positions, strengths and widths of individual lines are practically impossible to catalogue since there are literally (densely packed) thousands of them. Lines belonging to hot bands, which are transitions from excited vibrational levels, and isotopic bands further complicate the problem. A proper approach to take in such instances would be to measure the absorption coefficient itself over the range of wavenumbers, temperatures and pressures that are relevant to atmospheric remote sensing experiments. The ultimate goal in the line-by-line scheme is, after all, that of computing the absorption coefficient, a computation that is so desperately dependent on our knowledge, which we can never hope to possess totally adequately in the near future, of all of the parameters mentioned above and of their temperature and pressure dependence. Why not measure the absorption coefficient itself in the laboratory ? To illustrate the atttractiveness of this idea we present below two examples involving CFC-12 (CF₂Cl₂) and CFC-22 (CHClF₂). The spectra were measured with the Doppler-limited spectral resolution of a tunable diode laser spectrometer and using a cryogenically cooled absorption cell, both of which are adequately described in some of our publications.¹

© 1991 Optical Society of America