Influence of the finite duration of collisions on the infrared line shape

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Abstract
The influence of the finite duration of the collisions is analyzed for the pure rotational lines of a diatom–atom gas mixture and discussed vs the general trends of the anisotropic part of the intermolecular potential. The calculated line profiles, using curved classical trajectories and including all the orders of the interaction in the description of the time evolution of the dipole moment, show a significant deviation from the usual impact van Vleck–Weisskopf profiles as soon as the anisotropic potential exhibits a marked well. Such a deviation is consistent with the experimental results of Frenkel and van der Elsken for HCl–Ar mixture. At last, the shape of the rotational lines in the harmonic 0–2 vibrational band of HCl perturbed by xenon is calculated. In that case, the presence of a strong vibrational dephasing effect increases the influence of the finite duration of collisions and introduces a marked asymetry of the line shape.
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