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Pressure-induced rotational-vibrational U transitions (ΔJ=4) 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 $U(1)$ line, rough values are obtained for the hydrogen-molecule hexadecapolar moment and its derivative.
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Gibbs et al. (1974) studied this question.
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