Knowledge Bank

The infrared spectra of several isotopologues of the CO$2$-({\em para}-H$2$)$2$ trimer have been predicted by applying exact basis-set calculations to a global potential energy surface which is defined as a sum of the accurately known two-body {\em para}-H$2$--CO$2$ and {\em para}-H$2$--{\em para}-H$2$ potentials.\ (2010, submitted);~ K.\ Patkowski, W.\ Cencek, P.\ Jankowski, K.\ Szalewicz, J.B.\ Mehl, G.\ Garberoglio and A.H.\ Harvey, {\em J.\ Chem.\ Phys.} {\bf 129}, 094304 (2010).} These results are compared with new spectroscopic measurements, for which sixteen transitions have been assigned. A reduced-dimension treatment of the {\em para}-H$2$ rotation has been employed by performing an exact hindered-rotor average.\ (2010 submitted).}~ Three-body effects and the quality of the potential are discussed. We present a new technique for representing the three-dimensional {\em para}-H$2$ density in the body-fixed frame. It shown the two {\em para}-H$2$ molecules are localized much more closely together than is the case for the two He atoms in the analogous CO$2$--(He)$2$ system.