Far infrared absorption spectra in liquid and solid H2

The far infrared absorption spectra of hydrogen have been measured in solid and liquid phases in the frequency range 300-800 cm-1. We have found a remarkable similarity between the liquid and solid spectra. In the solid phase, we have performed measurements at different ortho-H2 concentrations in order to investigate the influence of ortho-H2 molecules. In particular, we have studied the behaviour of the S(O) line at low ortho-H2 concentrations. We found that the rotational exciton picture describes our results well