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42121-AC6
Fluorinated Radicals and Interstellar Molecules
Introduction. Our work consists of using the sensitive and versatile technique of pulsed-jet Fabry-Perot Fourier transform microwave (FTMW) spectroscopy to study the structure, dynamics, and electronics of a number interesting molecular systems. During the granting period of September 1, 2006 - August 31, 2007 the work in our laboratory consisted of four themes: 1) the study of radicals and other unstable molecules produced in a high voltage discharge immediately following the supersonic expansion of the molecules into the vacuum chamber, 2) the study of the dynamics and structures of weakly bound complexes, 3) collaborating with visitors to the lab on joint projects, and 4) making the laboratory and the FTMW spectrometer available to visitors for their own microwave spectroscopic experiments. Radicals and other unstable molecules. F2C-C≡N. We have completed a study of the cyanodifluoromethyl radical which is isoelectronic with our already published 1,1-difluoro-2-propynyl radical, F2C-C≡CH. The radical's rotational spectra shows a rich splitting of the transitions consisting of “fine structure” due to the electronic spin of the radical coupling with rotation, and the “hyperfine structure” due to the coupling of the nuclear spins of the hydrogen and the fluorine nuclei with the electronic spin of ½ in addition to the nuclear quadrupole coupling splitting of the I = 1, 14N. While the pure rotational transitions tell us about the geometric structure of the difluoropropargyl radical, the fine and hyperfine splittings yield information about the electronics of the radical. Unlike F2C-C≡CH, F2C-C≡N is non-planar. The bonding of the fluorine atoms to the methyl carbon is greatly influenced by the substitution of N for CH at the other end of the molecule. HGeBr. We have begun a collaboration with Dennis Clouthier and his graduate student Fumie Sunahori from the University of Kentucky. Fumie visited the lab for three weeks in July 2007 to work on this and other projects. We have previous published work on HSiCl and HGeCl, so the work on bromogermylene is a natural extension for us. Clouthier and Sunahori have observed this molecule in high resolution electronic spectra, so we followed their procedure in the production of this unstable triatomic: a high voltage discharge following supersonic expansion of a dilute mixture of H3GeBr in argon. Preliminary spectra have been observed and assigned. CCP. This project is also in collaboration with Clouthier and Sunahori. CCP is a linear 2Π1/2 radical and a possible candidate for interstellar detection. Following the procedure of Clouthier, we have attempted to produce the radical by a discharge of a jet of a mixture of PCl3 and methane in an argon carrier gas. No spectra unambiguously assignable to CCP has yet to be observed. Weakly bound complexes. (OCS)2. The lowest energy, non-polar isomer of (OCS)2 has long been known from IR spectroscopy, while the “long-anticipated polar isomer of the OCS dimer” has only been deduced from qualitative beam refocussing experiments. This, despite many attempts by microwave spectroscopist to find the polar isomer. After the initial detection in the infrared by Afshari and coworkers, we have found the higher energy, polar isomer of (OCS)2 by the “trick” high pressure expansion of dilute OCS in helium. A surprisingly strong microwave spectrum of Cs (OCS)2 has been observed and assigned. This work was published in the Journal of Chemical Physics. (N2O)2. The higher energy polar isomer was also found by Afshari and coworkers in the infrared and then by us in the microwave. Again, the trick is to expand in helium which allows for the higher energy isomers to coexist with the lowest energy form in a beam whose rotational temperature is ~ 1 K. Since the dimer has four spin 1 14N nuclei, each rotational transition has hundreds of unresolved hyperfine components. The 15N containing isotopomers were studied in collaboration with Nicholas Walker and Anthony Legon at the University of Bristol. Many weakly bound (van der Waals) complexes have been studied in the lab. During the year covered by this period of the PRF grant we have investigated, among others, the structure and dynamics cyanoacetylene, HCCCN, complexing with itself, neon, carbon monoxide, and carbon dioxide. Collaborations with visiting scientists. With Adjunct Professor Karen Peterson of San Diego State University, we have just submitted for publication in the Journal of Chemical Physics the study of the complexes of argon and neon with the weakly polar small hydrocarbon, propane. Karen has visited the lab for the past three summers. New projects with her are underway. Professor Robert Bohn and his students of the University of Connecticut visit the laboratory to work on multi-conformational molecules. Former student, Professor Lu Kang, of Union College, Kentucky, is a frequent visitor to the laboratory.
