HOW DIFFERENT ARE {\it ORTHO} AND {\it PARA} HYDROGEN? A COMPUTATIONAL EXAMINATION OF POTENTIALS, BOUND STATES, AND SCATTERING OF HYDROGEN COMPLEXES

Abstract

The interaction between molecular hydrogen and other molecules is studied through {\it ab initio} calculations with a focus on differences in behavior between {\it ortho} and {\it para} hydrogen. These differences manifest themselves in various ways, including in the rotational spectra of complexes}, J. Chem. Phys. {\bf 127}, 054305 (2007).}$^{,}$}, J. Chem. Phys. {\bf 115}, 5155 (2001).} and in pressure broadening cross sections.}, 4069 (2000).} Two specific systems, H$_{2}$-HCN and H$_{2}$-OCS, will be examined. For H$_{2}$-HCN, a new 4-D potential surface will be presented along with bound state and scattering calculations, while for H$_{2}$-OCS new calculations utilizing a previously presented potential} will be discussed. These two systems display markedly different ground state geometries that lead to different behavior of the {\it ortho} and {\it para} hydrogen complexes. In addition to the specific systems a more general discussion will examine the effect of potential anisotropy and ground state geometry on the properties of hydrogen complexes and how the differences between {\it ortho} and {\it para} interactions can be used.