The S(0) line in solid H2

The far infrared absorption spectrum of solid H2 has been measured in the frequency region of the S(0) line. We have performed measurements at different ortho H2 concentrations in order to investigate the influence of ortho H2 molecules. By increasing the ortho H2 concentration Co from Co = 10% up to 75%, we found that the excitonic absorption is the dominant feature of the S(0) line at low Co values, but it still exists when Co is relevant.