Hexadecapolar U-branch transitions in the infrared fundamental band of gaseous hydrogen at 77 K

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Abstract
U‐branch transitions corresponding to the rotational selection rule ΔJ=+4 in the collision‐induced fundamental band of normal H2 at 77 K have been investigated for gas densities in the range 300–520 amagat with a 2 m absorption cell. These transitions, arising from the hexadecapolar induction mechanism in the colliding pairs of molecules, occur in the high wave number tail of the overlap and quadrupolar transitions of the band and include primarily single transitions U 1(J) and double transitions Q 1(J)+U 0(J), J=0 and 1, at 77 K. The experimental absorption profiles were analyzed by assuming a new expression for the contribution of the total wing of the overlap and quadrupolar transitions and a dispersion type function as well as a Levine–Birnbaum function for the U transitions, and the characteristic half‐width parameters δ u of the dispersion function and δ′ u of the Levine–Birnbaum function have been obtained. The experimental value of the binary absorption coefficient of the U 1(1) transition, derived from the profile analysis, is 2.40×10−10 cm−1 amagat−2, which is in good agreement with the theoretical value.