TESTING THE VALIDITY OF THE OPTICAL DIFFUSION-COEFFICIENT - LINE-SHAPE MEASUREMENTS OF CO PERTURBED BY N2

Using a high-resolution difference-frequency spectrometer, we have stu died the shape of four infrared lines of CO, highly diluted in N2. We have approached the analysis from two perspectives. In the first, the spectral profile of an isolated line is empirically represented by a v ariation from the ''standard'' model in which the mass-diffusion const ant is replaced with a pressure- and line-dependent ''optical'' diffus ion constant. In the second, we abandon the concept of an ''optical'' diffusion constant and replace it with a physically more tenable hypot hesis that the departures from the standard model are due to a slight deviation from the usual exponential decay used to describe the collis ion broadening of spectral lines. This shifts the focus of the discuss ion from an analysis of the translational dynamics to an analysis of t he dynamics of the internal degrees of freedom.