Finite duration of collisions and vibrational dephasing effects on the Ar broadened HF infrared line shapes: Asymmetric profiles

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Abstract
The existence of an asymmetry for the HF rovibrational absorption isolated lines induced by Ar pressure is clearly observed. This confirms the expected behavior based on a previous theoretical analysis of the finite duration effect on the molecular line shapes in the core region at moderate densities. The observed profile is well represented by the addition to the usual Lorentzian line shape of a dispersion component. This component is proportional to a characteristic parameter, linear with respect to the density of perturber and explicitly connected to the intermolecular potential. The a priori calculation of this parameter from an empirical potential leads to a super-Lorentzian shape in the low frequency side in agreement with the experiment. Moreover, the expected increase of the asymmetry when going from the fundamental to the harmonic band is well observed. Such an increase results from the modification of the vibrational dephasing process due to molecular anharmonicities.