The Low Frequency Broadband Fourier Transform Microwave Spectroscopy of Hexafluoropropylene Oxide, CF 3 CFOCF 2 Lu Kang 1, Steven T. Shipman 2, Justin L. Neill 2, Alberto Lesarri 3, and Brooks H. Pate 2 1 : Department of Natural Sciences, Union College, KY 40906, USA 2 : Department of Chemistry, University of Virginia, VA 22904, USA 3 : Departmento de Quimica Fisica, Universidad de Valladolid, SPAIN

A challenge of FP-FTMW below 4 GHz  Fabry-Perót cavity: Q ~ 10,000  Fresnel number:  Solutions to the low frequency bands  Increase a: Arunan, Emilsson, Gutowsky J. Chem. Phys. 101, 861, (1994)  Decrease R: Etchison, Dewberry, Kerr, Cooke J. Mol. Spectrosc. 242, 39, (2007)  Cylindrical resonator: TE 01 mode Storm, Dreizler, Consalvo, Grabow, Merke Rev. Sci. Instrum. 67(8), 2714, (1996)

Chirped-Pulse FTMW spectrometer (WF08) L P F SS –AMP AWG 7102 DG 535 CDCD ABAB 10 MHz Ref. TDS 2040 TDS 6124C LN-AMP SPST CP-FTMW is not a FP cavity based technology!

Hexafluoropropylene Oxide — HFPO  Material sciences, :CF 2  Polymer chemistry  Simple structure  Dipole moments a-axis: D b-axis: 0.15 D c-axis: 0.40 D

Ab initio calculations & experiments  Density Functional Theory (DFT) calculation  Gaussian 03: B3LYP/ G(d,p)  Sample: HFPO – SynQuest Lab. Inc.  ~ 0.3% 1.5 atm  CP-FTMW spectrometer: 2.0 – 8.5 GHz  Average 10,000 shots in 45 min.  SS-AMP(4W) / TWTA(300W)  FP-FTMW spectrometer: 8.0 – 26 GHz

Analysis  Spectra assignments: 5 HFPO isotopologues  Plusquellic’s JB95 & Pickett SPFIT/SPCAT  Watson’s A-reduction Hamiltonian  Structural analysis  Watson’s mass dependent r m (2) structure  Kisiel’s STRFIT

DFT calc. [1], [2] [1][2] Main-HFPO 13 C 1 -HFPO 13 C 2 -HFPO 13 C 3 -HFPO 18 O-HFPO A 0 (MHz) (11) (44) (41) (41) (45) B 0 (MHz) (5) (25) (27) (23) (26) C 0 (MHz) (5) (30) (30) (27) (35) Δ J (Hz) (18)54.6(19)55.0(19)54.5(16)54.5(24) Δ JK (Hz) (86)109.5(94)107.7(91)105.4(82)96.0(98) Δ K (Hz) (15)-20(10)-19(13)-11.3(99) [3] δ J (Hz) (61)8.38(75)8.79(78)8.59 (62)8.3(10) δ K (Hz) (13)-260(19)-261(19)-251(16)-247(23) σ [4] (kHz) [4] # of lines [ 1] [ 1] The calculation was done by B3LYP/ G(d,p) method using Gaussian 03 program package. [2] [2] All calculated constants are derived from the optimized equilibrium molecular structure. [3] [3] Fixed to be the values obtained from the dominate isotopologue. [4] [4] The standard deviation of the fit using Pickett’s SPFIT suite of program. The spectroscopic constants of HFPO

Molecular skeleton structure of HFPO DFT r e struct.Exp. r m (2) struct. [1] r(CF 3 – CF) / Å (4) r(CF – CF 2 ) / Å (5) r(CF 2 – O) / Å (2)  (CF 3 –CF–CF 2 ) / º (3)  (CF–CF 2 –O) / º (2) Φ(CCC – CCO) / º (3) [1] The fluorine atoms related structural parameters are fixed to be the optimized values from the DFT calculation, B3LYP/ G(d,p).

Summary  Microwave spectra of HFPO: 2.0 – 26 GHz  CP-FTMW: effective in S & C bands (2 – 8 GHz)  a-type transitions can be observed (μ a < 0.1 Debye)  All 13 C (1.07%) isotopologues can be measured in natural abundance using CP-FTMW spectrometer!  Determined the skeleton r m (2) geometry of HFPO  DFT calc. agrees with exp. measurements

Acknowledgement  John B. Stephenson Fellowship, 2007 Appalachian College Association (ACA)  Prof. Brooks H. Pate’s group  Dr. Richard D. Suenram (NIST/UVA)  Dr. Gordon G. Brown (Coker College, SC)  Audience