Microwave Spectroscopy of Weakly Bound Molecular Complexes

80 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.The pure rotational high resolution microwave spectra of weakly bound molecular complexes are discussed. These complexes, consisting of a polar linear molecule and a rare gas atom or other molecule as the bound partner, have binding energies ranging from 0.2 to 6.0 kcal/mole. Formation of the complexes is achieved by a molecular free jet expansion of the monomeric components in an inert carrier gas. The expanding gas is directed into a Fabry-Perot cavity where the rotational transitions of the species of interest are excited with a microwave pulse. The subsequent coherent molecular emission can be detected and analyzed to yield structural and electronic information about the complex.The Fabry-Perot pulsed Fourier transform microwave technique is briefly outlined in the first chapter. This method was used for all the experiments discussed in this thesis. In Chapter II the krypton-hydrogen fluoride van der Waals molecule is discussed. The rotational spectra of eight isotopic species are assigned and the molecular structure and intramolecular potential are interpreted in light of the spectroscopic constants. The first observed rare gas nuclear quadrupole coupling (83-Kr), due to the electronic field gradient at the krypton nucleus, results from Sternheimer type shielding rather than charge transfer in the KrHF molecule.Chapter III contains the spectroscopic data and derived constants for the ground vibrational state of the gas phase linear hydrogen-bound hydrogen cyanide dimer. This work resolves the hyperfine structure due to the nitrogen nuclear electric quadrupole moment in the dimer for the first time. Differences in the nuclear quadrupole coupling constants at the binding and non-binding nitrogen sites are attributed to electronic effects within the HCN subunits. Work in progress on a search to observe the dimer in interstellar dust clouds is also described.The complex between cyclopropane and hydrogen fluoride is found to be hydrogen-bound and is discussed in Chapter IV. The heavy-atom-planar structure of the complex is uniquely determined from the isotopic species studied. The force constant and well depth of this complex are compared to those of other hydrogen-bound complexes as well as non-hydrogen-bound species. Finally the last chapter contains results of two related projects.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD