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Rotational spectroscopic studies of C-H · · · F interactions in the vinyl fluoride · · · difluoromethane complex
No full textRotational spectra of the normal isotopic species and three (13)C isotopologues of the 1:1 complex between vinyl fluoride (CH2 ═ CHF) and difluoromethane (CH2F2) have been measured using 480 MHz bandwidth chirped-pulse Fourier-transform microwave spectroscopy in the 6.5-20 GHz region. A structure for this dimer has been determined by fitting the moments of inertia of all isotopologues and confirmed by calculation of Kraitchman single isotopic substitution coordinates. The structure is consistent with that determined by ab initio geometry optimization at the MP2/6-311++G(2d,2p) level and has the difluoromethane subunit located on the CHF side of the vinyl fluoride subunit with three C-H · · · F contacts and with the hydrogen atoms of the CH2F2 straddling the vinyl fluoride symmetry plane
Reduced bandwidth chirped-pulse microwave spectroscopy for analysis of weakly bound dimers: Rotational spectrum and structural analysis of CH2ClF⋯FHCCH2
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Weak interactions and CO2 microsolvation in the cis-1,2-difluoroethylene...CO2 complex
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Previous issue date: 6The need for a deep understanding of chem{CO_2} interactions is significant given the importance of supercritical chem{CO_2} (sc-chem{CO_2}) as a green solvent. Fluorinated compounds often have higher solubility in sc-chem{CO_2} than their hydrocarbon analogs, and the reasons for this are not well understood. Investigations of dimers of one chem{CO_2} molecule with a simple fluorinated hydrocarbon provide an initial step towards understanding the complex balance of forces that is likely to be present as a larger solvation shell of sc-chem{CO_2} is built._x000d_
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The weakly bound dimer {it cis}-1,2-difluoroethylene...chem{CO_2} is the latest in a series of complexes of chem{CO_2} with fluorinated ethylenes that has recently been studied using chirped-pulse (CP) Fourier-transform microwave spectroscopy. Unlike all previous members of the series, the observed structure of {it cis}-1,2-difluoroethylene...chem{CO_2} is nonplanar, with chem{CO_2} sitting above the ethylene plane and crossed relative to the C=C bond. This nonplanar arrangement is consistent with predictions made using symmetry adapted perturbation theory (SAPT), where the dispersion energy of the nonplanar structure is significantly more favorable than for a structure where chem{CO_2} lies in the same plane as the ethylene moiety. Observed transitions are doubled as a result of chem{CO_2} tunneling between equivalent positions above and below the ethylene plane, leading to inversion of the dipole moment component. Observed transitions for the most abundant isotopologue have been fitted to a two state Hamiltonian to give an energy difference between tunneling states of MHz, and analysis using Meyer's one dimensional model to determine the barrier to inversion is presently in progress
STRUCTURE DETERMINATION AND CH…F INTERACTIONS IN H2C=CHF…H2C=CF2 BY FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY
Get PDFThe structure of the weakly bound dimer between fluoroethylene (FE) and 1,1-difluoroethylene (DFE) has been determined using a combination of chirped-pulse and resonant-cavity Fourier-transform microwave spectroscopy over a 7.5 to 19 GHz range. The rotational constants of the most abundant isotopomer were determined to be = 6601.14(35) MHz, = 833.3336(5) MHz and = 744.0217(5) MHz, and are in excellent agreement with predictions at the MP2/6-311++G(2d,2p) level. Observation of all four unique C isotopologues in natural abundance allowed for a full structure determination, showing that the dimer takes on a planar configuration with the H--C--F end of FE aligned with one of the F--C=C--H sides of DFE, forming two inequivalent CHF contacts. The dipole moment components ( = 0.9002(18) D, = 0.0304(80) D) were determined using Stark effect measurements and confirm the observed structure.Made available in DSpace on 2016-01-05T20:04:30Z (GMT). No. of bitstreams: 3
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New approaches to decoding rotational spectra: Applications to fluoroethylene microsolvation by CO2
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Previous issue date: 6Chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometers such as the instrument at the University of Virginia can acquire spectra with high sensitivity in a short amount of time. This necessitates new approaches to spectroscopic analysis to ensure identification of all species in each recorded spectrum. With an intensity range covering four orders of magnitude after averaging 1 million free induction decays, a recent spectrum of a fluoroethylene (FE)/CO2 mixture in the 2 – 8 GHz range has over 11,000 lines with signal-to-noise ratio above ∼2.5. These transitions may arise from a combination of monomer, dimer and larger cluster species, including low abundance isotopes and complexes with carrier gas, water or other contaminants.
Our current focus is identifying spectra of FE(CO2)n clusters, containing progressively larger numbers of CO2 molecules. Several methods have been used to facilitate identification of lines for these spectra, which are expected to lose 1-2 orders of magnitude of intensity for each increase in cluster size. These approaches include subtraction of transitions that are observed in the FE-only spectrum from the spectrum of the FE/CO2 mixture, visual identification of patterns characteristic of asymmetric molecules, and application of extended cross correlation (XCC) techniques.a In the XCC approach, several spectra with systematically varied conditions (such as pressure or concentration) are compared, and a combination of graphs and computerized algorithms is used to identify transitions that behave similarly under the changing conditions. In addition to applications for fundamental spectroscopic studies, this approach has potential application to identification of the components of complex mixtures
Engaging Undergraduate Students In Spectroscopy Research Via Development And Incorporation Of Advanced Data Analysis Techniques
Get PDFThe rapidity with which large amounts of spectroscopic data can now be collected is presently driving interest in developing techniques to improve the speed with which spectra can be analyzed. While desirable in a research setting to avoid bottlenecks in the lab, these techniques will also be essential to the commercialization of high resolution spectroscopic methods for analysis of complex mixtures. At the same time, many undergraduate students are intrigued by the concept of data analytics and attracted by the growing job market related to this field. We will present our incorporation of analysis techniques appropriate for large data sets into undergraduate spectroscopy research experiences. Through analysis of high sensitivity microwave spectra of complex mixtures of weakly bound complexes, undergraduate students from a wide range of majors gain skill sets that put them ahead of their peers in areas such as problem solving, basic coding, and computer skills (Excel, DOS, Linux, Python, Mathcad). The majority of spectroscopy undergraduate research students at Eastern Illinois University do not go on to chemistry careers, and these additional skills that they learn provide excellent preparation for a wide range of career choices.Made available in DSpace on 2021-09-24T21:08:48Z (GMT). No. of bitstreams: 2
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Previous issue date: 2021-06-2
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