Knowledge Bank

Any description of the mechanisms responsible for solvent effects or pressure effects in spectroscopy requires knowledge of the electronic structure for the molecule for both the ground- and excited-states involved in the transition. The electronic structure for the molecule is typically characterized from determinations of the dipole moment and polarizability. Variations in these quantities with respect to solvent changes in the ground-state have been extensively studied using the Claussius-Mossotti relation. The corresponding excited-state quantities can be measured using electrochromism. In this technique, intense electric fields are used to partially orient a vapor phase sample which results in altering the absorption profile. From this effect, the excited-state dipole moment and polarizability can be determined. Electrochromism was use to determine the excited-state properties for the 192.2 nm band and 174 nm band for thiirane (ethylene Sulfide) assigned as the $4p\leftarrow n$ and $3d\leftarrow n$ Rydberg Transitions. The variations in the properties with respect to increasing the pressure of a nonpolar dielectric gas $(SF6orCF4)$ are discussed in terms of intermolecular potentials for the excited-states and possible mechanisms for interactions.