The Low Frequency Broadband Fourier
Transform Microwave Spectroscopy of
Hexafluoropropylene Oxide, CF3CFOCF2
Lu Kang1, Steven T. Shipman2, Justin L. Neill2,
Alberto Lesarri3, and Brooks H. Pate2
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, 47005 SPAIN
A challenge of FP-FTMW below 4 GHz

Fabry-Perót cavity: Q ~ 10,000
a2
 Fresnel number: N 
1
R

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: TE01 mode
Storm, Dreizler, Consalvo, Grabow, Merke
Rev. Sci. Instrum. 67(8), 2714, (1996)
Chirped-Pulse FTMW spectrometer (WF08)
CP-FTMW is not a FP cavity based technology!
TDS 2040
10 MHz Ref.
AWG 7102
TDS 6124C
C D
LPF
DG 535
LN-AMP
A B
SS –AMP
SPST
Hexafluoropropylene Oxide — HFPO
 Material sciences, :CF2
 Polymer chemistry
 Simple structure
 Dipole moments
a-axis: 0.066 D
b-axis: 0.15 D
c-axis: 0.40 D
Ab initio calculations & experiments

Density Functional Theory (DFT) calculation
 Gaussian

Sample: HFPO – SynQuest Lab. Inc.
~

03: B3LYP/6-311++G(d,p)
0.3% HFPO/Ne @ 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
50
0.4
13C-HFPO:
220 - 110
The 2.0 - 8.5 GHz spectra
of HFPO isotopologues
10,000 averages in 45 min.
C3
0.3
40
C2
C1
0.2
Intensity (mV)
0.1
30
0.0
7597.5
7599.0
7600.5
20
10
0
2000
3000
4000
5000
6000
Frequency (MHz)
7000
8000
Analysis

Spectra assignments: 5 HFPO isotopologues

Plusquellic’s JB95 & Pickett SPFIT/SPCAT

Watson’s A-reduction Hamiltonian
Hˆ  A J 2  B J 2  C J 2
rr
0 a
0 b
0 c
Hˆ cd   J J 4   JK J 2K a2   K K 4a  2 J J 2 (J b2  J c2 )

  K J a2 (J b2  J c2 )  (J b2  J c2 )J a2


Structural analysis

Watson’s mass dependent rm(2) structure

Kisiel’s STRFIT
The spectroscopic constants of HFPO
DFT calc. [1], [2]
Main-HFPO
13C -HFPO
1
13C -HFPO
2
13C -HFPO
3
18O-HFPO
A0 (MHz)
2195.17
2217.04887(11)
2216.87825(44)
2214.65764(41)
2216.82656(41)
2187.44973(45)
B0 (MHz)
1088.27
1101.48958(5)
1097.80870(25)
1101.55450(27)
1096.82685(23)
1090.69436(26)
C0 (MHz)
925.60
936.60131(5)
933.89940(30)
936.24432(30)
933.18612(27)
933.87117(35)
ΔJ (Hz)
55.22
54.98(18)
54.6(19)
55.0(19)
54.5(16)
54.5(24)
ΔJK (Hz)
103.71
107.51(86)
109.5(94)
107.7(91)
105.4(82)
96.0(98)
ΔK (Hz)
-17.93
-19.8(15)
-20(10)
-19(13)
-11.3(99)
[3]
δJ (Hz)
8.54
8.493(61)
8.38(75)
8.79(78)
8.59 (62)
8.3(10)
δK (Hz)
-270.53
-265.5(13)
-260(19)
-261(19)
-251(16)
-247(23)
σ[4] (kHz)
---
1.4
1.3
1.4
1.5
2.0
# of lines
---
364
66
69
71
49
[1]
The calculation was done by B3LYP/6-311++G(d,p) method using Gaussian 03 program package.
[2] All calculated constants are derived from the optimized equilibrium molecular structure.
[3] Fixed to be the values obtained from the dominate isotopologue.
[4] The standard deviation of the fit using Pickett’s SPFIT suite of program.
Molecular skeleton structure of HFPO
DFT re struct.
[1]
Exp. rm(2) struct.[1]
r(CF3 – CF) / Å
1.532
1.546(4)
r(CF – CF2) / Å
1.460
1.451(5)
r(CF2 – O) / Å
1.380
1.374(2)
(CF3–CF–CF2) / º
126.6
126.2(3)
(CF–CF2–O) / º
60.1
59.3(2)
Φ(CCC – CCO) / º
101.2
103.0(3)
The fluorine atoms related structural parameters are fixed to be the optimized
values from the DFT calculation, B3LYP/6-311++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 (μa< 0.1 Debye)

All 13C (1.07%) isotopologues can be measured in
natural abundance using CP-FTMW spectrometer!

Determined the skeleton rm(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