Collision-induced absorption spectra of molecular hydrogen in the second overtone region at 77, 201 and 298 K

Xiang, Fan (1992) Collision-induced absorption spectra of molecular hydrogen in the second overtone region at 77, 201 and 298 K. Masters thesis, Memorial University of Newfoundland.

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Abstract

The collision-induced absorption spectra of molecular hydrogen in its second overtone region were recorded with a ~ 2.0 m high-pressure low-temperature absorption cell for gas densities up to 1000 amagat at 77, 201 and 298 K. The occurrence of the dip at Q₃(1) with characteristic low- and high- wavenumber components Qp and Qr, observed for the first time in the 3-0 band at different temperatures, clearly shows the contribution of the short-range electron-overlap interaction of the collisions to the 3-0 band in contrast to the 2-0 band of H₂. In addition to the overlap components, the observed spectra consist of the long-range quadrupole-induced transitions of the type Q₃(J)+Q₀(J), S₃(J)+Q₀(J), Q₃(J)+S₀(J), Q₂(J)+Q₁(J), S₂(J)+Q₁(J), Q₂(J)+S₁(J) and S₂(J)+S₁(J), where the subscripts 0 to 3 indicate Δv, the change in the vibrational quantum number. -- An analysis of the observed profiles was performed by using the Levine-Birnbaum intracollisional line-shape function [Phys. Rev. 154, 86 (1967)] and the Van Kranendonk intercollisional line-shape function [Can. J. Phys. 46, 1173 (1968)] for the overlap-induced transitions, and the Lorentz line-shape function as well as the Birnbaum-Cohen line-shape function [Can. J. Phys. 54, 593 (1976)] for the quadrupole-induced transitions. Very good agreement between the experimental absorption profiles and the calculated profiles was obtained by reducing the matrix elements of the quadrupolar moment <0J|Q|v’J’> for Δv= 2 and 3 by a factor 0.68 and by treating the relative intensities of the three groups of transitions, namely, the overlap transitions, the quadrupolar single transitions and the quadrupolar double transitions, as independent parameters. From this analysis the characteristic half-width parameters δa and δc for the overlap components, δq of the Lorentz line-shape function, and δ1 and δ2 of the Birnbaum-Cohen line-shape function for the quadrupole components have been determined. -- The analysis of the profiles described above reveals some excess absorption in the band around 12,460 cm⁻¹. As the area under the absorption profile of this excess absorption is found to be proportional to the cube of the density of H₂, it is interpreted as arising from the triple transitions Q₁(J)+Q₁(J)+Q₁(J). This represents the first observation of simultaneous transitions involving three molecules in collision-induced spectra. Profiles resulting from the triple-collision transitions were also analyzed satisfactorily by using the Lorentz line-shape function as well as Birnbaum-Cohen line-shape function.

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