Knowledge Bank

The intermolecular potential surfaces of the $H2$ - rare qas pairs are perhaps the best $characterized1$ of any triatomic system, thanks in part to previous mid-infrared $spectra2$ of the $H2-$, and $D2$-rare qas Van der Waals molecules. These spectra accompany the various rotation-vibration transitions in the $v=1-0$ fundamentals of $H2(=2.2\mu m)$ and $D2(=3,2\mu m)$ and they are observed in low-temperature long-path absorption experiments. Similar spectra should accompany the pure rotational $H2$ and $D2$ Lines in the fat infrared $(16-60\mu m)$, and the first such experiments are the subject of this talk. The usual far infrared difficulties with exotic window materials, low source brigtness, and low detector sensitivity make this work more difficult than that in the mid-infrared. The $S(0)(-354cm-1)$ and $S(1)(-587cm-1)$ spectra of $H2-Ar$ have already been observed, and they should ultimately result in even better potential surfaces for these systems. The same regions in the spsctrum of the dimer $(H2)2$ are also being studied, for the moment at 77 K (though lower temperature (15 K) experiments are also planned). These are of interest because of the observation of ($H2)2$ in Voyaget spececraft spectra of Jupiter and $Saturn.3$