Electromagnetic theories provide a tool to detect the origin of scattering in optical multilayers. Illumination and observation conditions that cause surface and bulk scatterings to have different behaviors are pointed out. Angular, wavelength, and polarization dependences are investigated for the location of structural irregularities at interfaces or in the bulk of a multilayer. Specific experiments can be designed.

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Taking advantage of a versatile set-up, combining pulsed pin hole or slit nozzle supersonic expansion with an external cavity quantum cascade laser, the rovibrational absorption spectrum of the SF dimer in the ν mode region has been revisited at high resolution under various experimental conditions in SF:He mixtures. Two new rotationally resolved spectral bands have been identified in the range of the parallel band of the dimer spectrum in addition to that previously reported. Among these three spectral features, two of them are assigned to conformations of the dimer (noted #1 and #2), clearly distinguished from their different S-S interatomic distances, i.e. 474 and 480 pm respectively. The third one is assigned to a (SF)-He complex, from comparison with additional experiments in which (SF)-Rg heterotrimers (Rg = Ne, Ar, Kr, Xe) are observed. A schematic picture of the potential energy landscape of the SF dimer in terms of a nearly flat surface is proposed to account for the conformational relaxation observed in the expansions and for the structure of the (SF)-Rg heterotrimers, which are exclusively formed from the conformer #2 dimer. Although modelling qualitatively supports this picture, much effort has still to be achieved from a theoretical point of view to reach a quantitative agreement with the present benchmark experimental data both in terms of structure and energetics.