Energy level pressures, confined atoms

High resolution IR spectroscopy is confined to the study of atoms and molecules in the gas phase at low pressures, where the interaction energy between particles is orders of magnitude lower than in the condensed phases. The intermolecular interactions broaden the energy levels, and, consequently, the spectrcil lines, preventing the observation of finer details in the spectra. In the IR region the width of the spectral lines in the gas phase is caused mainly by the Doppler effect and by the broadening due to... 

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