Quadrupolar double transitions S1(J)+S(J) in the infrared fundamental band of molecular hydrogen at 77 K

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Abstract
Double transitions S1(J)+S0(J) corresponding to the vibrational–rotational transition in one molecule and a rotational transition in the other molecule, occurring simultaneously in a colliding pair, have been observed in the infrared fundamental band of normal H2 at 77 K for gas densities in the range 100–320 amagat with a 2 m absorption cell. These transitions arise because of the contribution to the intermolecular interaction by the anisotropic component of the polarizability of one molecule in the quadrupole field of the other and occur in the high wave number tail of the S1(J) and Q1(J)+S0(J) components of the band. The experimental profiles were analyzed by assuming appropriate line shape functions and using the theoretical matrix elements of the quadrupole moment, isotropic polarizability, and anisotropy of the polarizability, of the H2 molecule. From this analysis the characteristic half-width parameter δq and the binary and ternary absorption coefficients of the S1(J)+S0(J) transitions have been obtained. The value of δq obtained in the present work is in agreement with the one obtained for the S1(J) and Q1(J)+S0(J) components of the lower density profiles of the band at 77 K reported earlier from our laboratory [S. P. Reddy, G. Varghese, and R. D. G. Prasad, Phys. Rev. A 15, 975 (1977)]. The experimental value of the binary absorption coefficient of S1(1)+S0(1) is 1.3×10−9 cm−1 amagat−2, which is in close agreement with the theoretical value.