Frank Marshall

Microwave Spectra and Structure of Ar-1,3-Difluorobenzene

The microwave spectrum of the dimer Ar-1,3-difluorobenzene from 2 to 18 GHz is reported. The spectrum has been observed using a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer that has recently been expanded to include the 2-6 GHz region of the electromagnetic spectrum. Details of this upgraded spectrometer are reported. Eighty-seven transitions were observed for the parent dimer spectrum, which was adequately fit to a semirigid rotational Hamiltonian consisting of A, B, and C as well as four quartic centrifugal distortion constants. Observations of 13C species in natural abundance were aided by utilizing smaller chirp ranges of 7-9 and 9-11 GHz for 1.9 million and 3.73 million averages, respectively. Assignment of 13C isotopologues allowed for determination of the Kraitchman coordinates of the carbon atoms as well as inertial fits of the complex. The quantum-chemical structure predicts an Ar to monomer center of mass distance of 3.48 Å, compared with 3.564(1) Å determined from experimental structural analysis. This new study indicates that in fluorinated benzene-Ar dimers, when the fluorines are separated by more carbon atoms, the Ar-ring center distance decreases.

THE COMPLETE HEAVY-ATOM STRUCTURE OF A CP-FTMW CHIRAL TAG PRECURSOR, VERBENONE

FRANK E MARSHALL, Department of Chemistry, Missouri University of Science and Technology, Rolla, MO, USA; CHANNING WEST, GALEN SEDO, Department of Natural Sciences, University of Virginia’s College at Wise, Wise, VA, USA; BROOKS PATE, Department of Chemistry, The University of Virginia, Charlottesville, VA, USA; G. S. GRUBBS II, Department of Chemistry, Missouri University of Science and Technology, Rolla, MO, USA.

AN INVESTIGATION OF THE DIPOLE FORBIDDEN TRANSITION EFFECTS IN BROMOFLUOROCARBONS AS IT PERTAINS TO 3-BROMO-1,1,1,2,2-PENTAFLUOROPROPANE USING CP-FTMW SPECTROSCOPY

As part of a series of bromofluorocarbon species and analogues, the microwave spectrum of the molecule 3-bromo-1,1,1,2,2-pentafluoropropane has been measured on a CPFTMW spectrometer located at Missouri S&T. The resultant spectrum is dense with transitions occurring at a rate of ≈1 transition/MHz! Within the spectrum, Br and Br isotopologues of multiple conformers of 3-bromo-1,1,1,2,2-pentafluoropropane have been identified. Rotational constants, centrifugal distortion parameters, nuclear quadrupole coupling constants and how each compare with theory for each conformer will be discussed. Due to the large quadrupolar moment of bromine, heavy, brominated molecules are good candidates for dipole-forbidden transitions. Previous studies with bromoperfluoroacetonea provided a rich spectrum full of dipole forbidden transitions that 3-bromo-1,1,1,2,2-pentafluoropropane does not share. This difference will be explained using structural considerations along with the matrix elements needed to enact these transitions.

A CHIRPED PULSE FOURIER TRANSFORM MICROWAVE (CP-FTMW) SPECTROMETER WITH LASER ABLATION SOURCE TO SEARCH FOR ACTINIDE-CONTAINING MOLECULES AND NOBLE METAL CLUSTERS

Microwave spectroscopic techniques have traditionally been part of the foundation of molecular structure and this conference. Instrumental developments by Brooks Pate and sourcing developments by Steve Cooke on these instruments have allowed for the dawning of a new era in modern microwave spectroscopic techniques.ab With these advances and the growth of powerful computational approaches, microwave spectroscopists can now search for molecules and/or cluster systems of actinide and noble metal-containing species with increasing certainty in molecular assignment even with the difficulties presented with spin-orbit coupling and relativistic effects. Spectrometer and ablation design will be presented along with any preliminary results on actinide-containing molecules or noble metal clusters or interactions.