We report on the collisional relaxation of the J = 3 <-- 2 rotational line
of CO induced by nitrogen and oxygen. Measurements have been made by using
a millimeter wave video-type spectrometer at several temperatures in the 24
0-400 K range. In the 20-400 mTorr pressure range investigated significant
deviations from the Voigt profile have been observed. The observed lineshap
es have been studied by means of a quasi-analytical Speed Dependent Galatry
Profile. This allows to point out a correlation between the parameters des
cribing the speed dependence of relaxation and the molecular diffusion. The
retrieved collisional relaxation coefficients and their temperature depend
ence both favourably compare to previous reported measurements. Theoretical
results obtained from the Robert-Bonamy collisional formalism and from the
Brownian motion theory allows to consider the possible origins of observed
lineshapes. (C) 2000 Elsevier Science B.V. All rights reserved.