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Title:Assignment of the microwave spectrum of 1,2-difluorobenzene…hcch: lessons learned from analysis of a dense broadband spectrum
Author(s):Peebles, Rebecca A.
Contributor(s):Pate, Brooks; Seifert, Nathan A.; Kang, Justin M.; Peebles, Sean A.; Grant, Mikayla L.; Nelson, Rebecca D.; Akmeemana, Anuradha
Subject(s):Structure determination
Abstract:Dimers of aromatic molecules with weak proton donors such as acetylene are prototypical systems for investigating weak CH$cdotspi$ interactions. A logical progression from our recent rotational spectroscopic studies of benzene�HCCH and fluorobenzene$cdots$HCCH was to study 1,2-difluorobenzene(1,2-dfbz)$cdots$HCCH, so the effect of increasing the number of electronegative substituents could be investigated. In this talk, structures of benzene, fluorobenzene, and 1,2-difluorobenzene complexed with HCCH will be compared, and the challenges and pitfalls encountered during assignment of the very rich chirped-pulse Fourier-transform microwave (CP-FTMW) spectrum will be discussed. The spectrum of a mixture of 1,2-dfbz and HCCH in a neon carrier was initially recorded using the CP-FTMW spectrometer at the University of Virginia. Transitions matching the patterns and approximate rotational constants predicted for 1,2-dfbz$cdots$HCCH were readily identified; however, efforts to fit the observed frequencies to an asymmetric top Hamiltonian were unsuccessful. A second CP-FTMW scan of only 1,2-dfbz monomer revealed that the transitions initially believed to be 1,2-dfbz$cdots$HCCH were actually present in both scans. Subtraction of lines common to both data sets revealed a previously unidentified pattern of transitions that have now been confirmed by isotopic substitution to belong to 1,2-dfbz$cdots$HCCH. The originally identified transitions are likely 1,2-dfbz$cdots^{20}$Ne, which has a similar mass to the HCCH complex. Ab initio calculations for 1,2-dfbz$cdots$HCCH and 1,2-dfbz$cdots$Ne lead to several possible orientations for each dimer with similar energies and rotational constants, and efforts to improve the computational methods and to reliably identify stationary points on the dimer potential energy surfaces are ongoing.
Issue Date:22-Jun-15
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:ACS
Genre:Conference Paper / Presentation
Date Available in IDEALS:2016-01-05

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