Testing the validity of the optical diffusion coefficient: Line-shape measurements of CO perturbed byN2

Abstract

Using a high-resolution difference-frequency spectrometer, we have studied the shape of four infrared lines of CO, highly diluted in N~. We have approached the analysis from two perspectives. In the first, the spectral profile of an isolated line is empirically represented by a variation from the "standard" model in which the mass-diffusion constant is replaced with a pressureand line-dependent "optical" diffusion constant. In the second, we abandon the concept of an "optical" diffusion constant and replace it with a physically more tenable hypothesis that the departures from the standard model are due to a slight deviation from the usual exponential decay used to describe the collision broadening of spectral lines. This shifts the focus of the discussion from an analysis of the translational dynamics to an analysis of the dynamics of the internal degrees of freedom.PACS number(s): 33.70. Jg, 35.20.Yh, 34.10.+x

Spectral Profiles for Atmospheric Absorption by Isolated Lines: A Comparison of Model Spectra with P- and R-Branch Lines of CO in N2 and Ar

“…It is the symmetric component of the experimental profiles that is analyzed here. For both hard-collision models we consider the narrowing parameter, z (for a definition, see for example (16)), to be determined by the mass diffusion constant (17). For CO-N 2 , the calculated narrowing parameter for the fundamental band of CO at 301 K is 7.19/atm.…”

Line Broadening and the Temperature Exponent of the Fundamental Band in CO–N2 Mixtures

“…The experiments described in this work were carried out using a difference-frequency laser spectrometer previously described by members of our group (23,28). The infrared radiation tunable in the 2.5-5.5 m is obtained by mixing the light from a frequency-stabilized Argon ion laser with the light from a Coherent 699-29, R6G dye laser.…”

Testing Lineshape Models: Measurements forv= 1–0 CO Broadened by He and Ar

“…Details of the independence between the time evolution of the translational LiIO 3 , difference frequency spectrometer have been given and internal degrees of freedom. Thus it reduces to the Voigt in (15,16). The essential characteristics of the spectrometer profile at low densities while capturing the essence of Dicke are a spectral resolution of 2 MHz (6 1 10 05 cm 01 ) and a narrowing at high densities.…”

“…We ignore the shifts. The expres-in our earlier publications (9,15,16).The speed-dependent models discussed above all assume statistical independence between phase changes and velocity changes, i.e., that conceptually to first order these changesThere is at present no model which combines the concepts of speed dependence and stawhere M is the confluent hypergeometric function. Here m tistical dependence and we are therefore forced to examine Å (n 0 3)/(n 0 1), a Å m p /m a , where m p and m a are the the influence of statistical dependence using a speed-indemasses of the perturber and active molecule, x is the speed pendent model.…”