Nuclear spin conversion of O2 doped solid normal H2 at 4.2 K: An empirical law to determine the ortho-H2 concentration by infrared absorption spectroscopy

We have studied the time evolution of IR spectra of solid normal H2 doped with O2 at 4.2 K. We have determined ortho concentration from IR integrated intensity ratio between the ortho double transitions at 4736 cm−1 and the para contribution to the double transitions at 4505 cm−1, supposing that an average experimental strength of these transitions can be defined. Within this frame, we propose an empirical relation between the ortho concentration and the experimental intensity ratio between the 4736 and the 4505 cm−1 absorptions.