Molecular orientation in superfluid liquid helium droplets: high resolution infrared spectroscopy as a probe of solvent-solute interactions

Reported here are three aspects of molecular stereochemistry associated wit h polar molecules in an exotic solvent, namely, superfluid liquid helium. I nfrared spectroscopy is used to study the nature of the solvent-solute and solute-solute interactions in this unique environment. First, we use an ext ernal dc electric field to orient the helium solvated polar molecules in th e laboratory frame of reference and we characterize this orientation using pendular state spectroscopy. Second, we present results that demonstrate no n-equilibrium self-assembly of polar molecules into linear chain structures , due to the mutual orientation imposed by the associated dipole-dipole int eractions. Finally, the spectroscopic results provide information on the an isotropic interactions experienced by the solvated molecules, which result in significant molecular orientation in the droplet frame of reference. Stu dies of this type provide important new insights into the nature of the int eractions between the molecules and the superfluid solvent.