EVIDENCE FOR A HEXADECAPOLE INTERACTION IN THE HYPERFINE SPECTRUM OF Lil

Abstract

Several years ago we used our molecular beam spectrometer to record the hyperfine spectrum of Lil. Attempts to fit the data to a set of molecular constants were close, but not quite satisfactory. Recently we have developed more refined techniques for fitting the lineshapes, and have refitted all the lines from the $^{7}Lil$ spectrum. With the improved line frequencies the data now fits nicely to a set of molecular constants, if a term representing the electric hexadecapole interaction of the iodine nucleus is included. A nuclear magnetic octupole interaction was also considered, but does not contribute significantly. To our knowledge this is the first time that a hexadecapole interaction significantly different from zero has been observed in a molecule.