Correlated and noncorrelated lineshape models under small lineshift condition:: Analysis of self-perturbed CH3D

The 14 transitions belonging to the P branch of the v(3) band of CH3D, near 1250 cm(-1), have been measured with a tunable diode-laser spectrometer. These lines, recorded at a total pressure ranging from 1 to 60 mbar, have been analyzed by means of soft and hard collision lineshape models. We emphasize the equivalence between the correlated and noncorrelated profiles, when the collisional lineshift may be neglected. As a result, new measurements of linestrengths, collisional self-broadening coefficients, and other parameters related to the Dicke effect are provided at room temperature. It is also shown that the instrumental distortions must be properly taken into account to avoid systematic errors on the fitted lineshape parameters, especially at low pressure. The broadening coefficients are compared with results calculated from a semiclassical theory, performed by considering, in addition to electrostatic interactions involving the octopole and hexadecapole moments of CH3D, the dispersion contributions. (C) 1998 Academic Press.