44177-AC6
Structure and Dynamics of Highly Excited Vibrational States of Complexes of Water and Hydrogen Fluoride
Molecular hydrogen is the most abundant species in the universe. The understanding of its interactions is of considerable importance in almost every area of science. We have investigated the binding of hydrogen to the polar molecule carbonyl sulfide. The study was quite complete in that every isotopomer of hydrogen and every metastable rotational energy level of hydrogen was studied. Very frankly we initially did not understand the spectral results of
o-H2 OCS which was the reason for this extensive study. The experiments were done by precision rotational spectroscopy so that hyperfine structure was resolved. Its analysis played an important role in developing our understanding. Considering just the ordinary hydrogen each to be examined the magnetically inactive form para-hydrogen in the J=0 rotational level and the magnetically active form ortho-hydrogen J=1 in which hyperfine structure is observed. For the pH2-OCS a single form is expected since J=O H2 is non-degenerate. This was readily found and fitted well to a simple rotational Hamiltonian. The ortho hydrogen, and search, J =1 is triply degenerate and this form of the H2-OCS complex was not well understood and what was surprising to us was that the rotational energy levels ortho H2 OCS were very similar to those of
para-H2-OCS. We had expected all states of ortho H2 OCS to have angular momentum. We saw no evidence of this angular momentum in our spectra the rotational energy levels of the complex started, in both complexes, with zero total angular momentum. The transitions of the ortho complex showed no internal angular momentum and were relatively similar to the para complex.
Upon more thoughtful analysis, which is presented in detail in the published paper on the species, the threefold degeneracy of ortho hydrogen binding to OCS sulfide is completely split under the point group CS where the only symmetry element is the plane containing the line of the OCS and they center mass of the H2. This group has only one dimensional representations thus we found a single level in which the hydrogen molecular axis lies approximately parallel to the carbonyl sulfide; the two other levels of J=1 one of which lying in the plane, with H2 axis perpendicular to the ground state observed, the other with the H2 perpendicular to the plane, were at high enough energies not to be populated and observed in the jet cooled spectra.
We believe this is one of the first complexes of hydrogen studied in enough detail to see hyperfine structure. The species HD with OCS and D2 with OCS were studied at a similar level of detail. In both of these species hyperfine structure is observed indicating showing the orientation of the system. HD is quite interesting since the only level thermally populated in the jet is again J=0 a spherical state. There is a slight indication of polarization observed with respect to deuterium hyperfine structure. D2-OCS shows the orientation in the J=0 form by the quadruple hyperfine structure, which is greater than in HD-OCS
