New Rotational Transition in the Hydrogen Molecule

Pressure-induced rotational-vibrational $U$ transitions ($\Delta J=4\mathrm{}$) of hydrogen gas have been observed for the first time at 195 K for densities in the range 180-300 amagat. The spectrum is interpreted in terms of a hexadecapolar induction mechanism, and from the experimental integrated absorption coefficient of the $U\left(1\right)\mathrm{}$ line, rough values are obtained for the hydrogen-molecule hexadecapolar moment and its derivative.