Advances in Use of p-H2 as a Novel Host for Matrix IR Spectroscopy

A review of recent advances in IR spectroscopy using p-H-2 as a matrix host in our laboratory is presented. The softness of this novel p-H, matrix host not only makes high-resolution spectroscopy feasible but also provides new applications. Molecular motion, such as the rotation of C2H4, internal rotation (torsion) of CH3OH, and rotation of CH3F about a single axis are characterized in this p-H, matrix. In contrast, no evidence for rotation of CH3I and CH3 was found. The diminution of the cage effect leads to the possibility of production of free radicals via either photolysis in situ or bimolecular reactions of molecules with atoms that are produced in situ from their molecular precursors. Taking advantage of these unique features, we identified the IR spectrum of CH3 produced from photolysis of CH3I and CH3S produced from photolysis of CH3SCH3 and CH3SSCH3. The reaction of Cl with CS2 in solid p-H-2 yields ClSCS instead of ClCS2. The reaction of Cl with HCOOH in solid p-H-2 yields only a complex, Cl center dot HCOOH, not HCl and HOCO. The presence of o-H-2 in trace proportions turned out to be an important factor in the interpretation of IR spectra of species embedded in solid p-H-2. Experimental techniques to minimize the amount of o-H-2 and to characterize its relative concentration with spectra of H2O center dot o-H-2 are discussed.