| Popis: |
The collision-induced absorption spectrum of normal hydrogen gas has been measured from 20–320 cm-1, at temperatures in the range 21–38 K, and pressures between 0.6 and 3 atmospheres, over an optical path of 52 and 60 meters. Under these conditions the pure translational absorption band is observed virtually isolated from the much stronger rotational lines. Observations were conducted using a new f/10 multi-reflection absorption cell cooled with the boil-off gas of liquid helium. The cell was coupled to a Fourier transform interferometer and spectra were obtained at a resolution of 0.24 cm-1. The spectra permit details of the submillimeter spectrum of H2 to be examined for the first time, and the R(0) line of HD at 89.2 cm-1 is observed in natural abundance. The absolute intensity of the H2 spectrum over the range 30–90 cm-1 is accurate to better than ±5% of the peak of the translational band. The measured translational spectrum can be synthesized within experimental error using the Birnbaum-Cohen lineshape. The temperature dependence of the translational band is discussed. The integrated intensity of the translational band is consistent with the Poll and Van Kranendonk theory of collision-induced absorption using a quantum mechanical pair distribution function based on a Lennard-Jones intermolecular potential. The integrated absorption increases with decreasing temperature in the range measured, and furthermore, it passes through a minimum between 38 and 77 K, the lowest temperature previously studied. |
