Slide 1
AUSTIN L. MCJUNKINS, K. MICHELLE THOMAS, APRIL RUTHVEN, AND
GORDON G. BROWNDepartment of Science and Mathematics, Coker
College, 300 E College Ave., Hartsville, SC 29550.
MH10ROOM-TEMPERATURE CHIRPED-PULSE FOURIER TRANSFORM MICROWAVE
(RT-CP-FTMW) SPECTRUM OF PYRIDINE
OutlineInexpensive room-temperature chirped-pulse Fourier
transform (RT-CP-FTMW) microwave spectrometer
Benchmark test - methanol
Room-Temperature spectrum of pyridine
Ideally suited for primarily undergraduate institution
(PUI)Inexpensive ($30 - $50K)No moving parts (easy to build and
use)Useful for undergraduate research and teaching labsInexpensive
Room-Temperature Chirped-Pulse Fourier transform (RT-CP-FTMW)
Microwave SpectrometerMW Synthesizer0Fourier TransformOscilloscope
(1 GHz)Chirped-PulseArbitrary FunctionGenerator(240 MHz)molecular
FIDstatic cell (12 feet of WRD-750 waveguide)to vacuummixerpower
divideramplifierDiode limiter1S. T. Shipman, J. L. Neill, B.
Kroncke, B. H. Pate, and P. Groner, Presentation at the
International Symposium on Molecular Spectroscopy, Columbus, OH,
USA, 2008.2Z. Kisiel, O. Dorosh, A. Maeda, I. R. Medvedev, F. C. De
Lucia, E. Herbst, B. J. Drouin, J. C. Pearson, S. T. Shipman, Phys.
Chem. Chem. Phys., 2010, 12, 8329-8339.
~480 MHz chirped pulse1W solid-state ampInexpensive
Room-Temperature Chirped-Pulse Fourier transform (RT-CP-FTMW)
Microwave SpectrometerWe have constructed a chirped-pulse Fourier
transform microwave spectrometer to use in our studies.Our
spectrometer creates a 240 MHz pulse by mixing a carrier frequency
(o) with a chirped pulse created by our arbitrary function
generator.The chirped pulse is then amplified and used to polarize
the molecules. After polarization, the free induction decay (FID)
is amplified and mixed down by our carrier frequency.The molecular
FlD (down converted) is digitized on our Oscilloscope (digital) and
the Fourier transform is taken in order to gain the frequency
spectrum.Using 480 MHz intervals, we can take a full 8GHz spectrum
(10-18GHz). Advantage of chirped pulse: you can take a lot of data
at once.
4MW Synthesizer0Fourier TransformOscilloscope (1
GHz)Chirped-PulseArbitrary FunctionGenerator(240 MHz)molecular
FIDstatic cell (12 feet of WRD-750 waveguide)to vacuum*Garry S.
Grubbs II, Christopher T. Dewberry, Kerry C. Etchison, Katherine E.
Kerr, and Stephen A. Cooke, Rev. Sci. Instrum., 2007, 78,
096106.~480 MHz chirped pulse1W solid-state ampdouble sideband
mixer*diode limiterAdvanced Control Components ACLM-4619FC36
Inexpensive Room-Temperature Chirped-Pulse Fourier transform
(RT-CP-FTMW) Microwave SpectrometerWe have constructed a
chirped-pulse Fourier transform microwave spectrometer to use in
our studies.Our spectrometer creates a 240 MHz pulse by mixing a
carrier frequency (o) with a chirped pulse created by our arbitrary
function generator.The chirped pulse is then amplified and used to
polarize the molecules. After polarization, the free induction
decay (FID) is amplified and mixed down by our carrier
frequency.The molecular FlD (down converted) is digitized on our
Oscilloscope (digital) and the Fourier transform is taken in order
to gain the frequency spectrum.Using 480 MHz intervals, we can take
a full 8GHz spectrum (10-18GHz). Advantage of chirped pulse: you
can take a lot of data at once.
5240 MHz Chirped Pulsebefore power amplifier
Our spectrometer OutlineInexpensive room-temperature
chirped-pulse Fourier transform (RT-CP-FTMW) microwave
spectrometer
Benchmark test - methanol
Room-Temperature spectrum of pyridine
you never forget your first
Methanol 202 3-13 (12178.60 MHz)(on cheap oscilloscope)
Benchmark: Methanol
165 12 174 13 20 2 3-1 351 5 41 4v0 = 12300MHz white
spectrum
v0 = 12304 MHzgold spectrum
For 20 2 3-1 3 :
12300 121.4 = 12178.6 MHz12304 125.4 = 12178.6 MHzSynthesizer at
12300 MHz (blue), Synthesizer at 12304 MHz (gold). This shows that
we saw real peaks and confirmed that our spectrometer worked. (
screenshot)
10Benchmark: MethanolAssignmentPrevious Observation
(MHz)2Shipman et al observation (MHz)1Current Work(MHz)165 12 174
1312229.40012229.35412229.36202 3-1312178.59312178.59912178.60514 -
51512511.00012511.20312511.191S. T. Shipman, J. L. Neill, B.
Kroncke, B. H. Pate, and P. Groner, Presentation at the
International Symposium on Molecular Spectroscopy, Columbus, OH,
USA, 2008.2L. H. Xu and F. J. Lovas, J. Phys. Chem. Ref. Data,
1997, 26, 17.
11OutlineInexpensive room-temperature chirped-pulse Fourier
transform (RT-CP-FTMW) microwave spectrometer
Benchmark test - methanol
Room-Temperature spectrum of pyridine
Previous MW work on Pyridine1,2G. O. Srensen: MW spectrum 8.5 27
GHz @ 25 C and -20 C1Ground vibrational stateQuadrupole Coupling
Constants
Ye et al.: 75 110 GHz and 260 370 GHzImproved constants for
ground stateAssigned 6 vibrationally excited states1G. O. Srensen,
J. Molec. Spectr., (1967) 22, 325-346.2Enyi Ye, Ryan P.A. Bettens,
Frank C. DeLucia, Douglas T. Petkie, and Sieghard Albert, J. Molec.
Spectr., (2005) 232, 61-65.
Room-Temp Spectrum of Pyridine1,2
10,000 averages; ~5 mTorr; 25 C~ 10 sec/step, 35 (overlapping)
stepsRoom-Temp Spectrum of PyridineGround Vibrational State1G. O.
Srensen, J. Molec. Spectr., (1967) 22, 325-346.JKa KcJKa Kc
Frequency (MHz)Previous Work(MHz)144 142 210288.62119 2119
310383.003227 53227 610569.5055 153 211164.003832 63832
711269.00108 2108 311398.502521 42521 511444.001815 31815
411491.504437 74437 811762.9197 297 312301.5012301.4966 164
212342.0012341.193126 5 3126 612621.001714 31714 412990.0086 286
313070.002420 42420 513297.5013297.443731 63731 713535.0413535.3275
275 313688.0077 175 213861.0013860.4864 264 314149.504336 74336
814214.0214213.581613 31613 414419.5053 253 314464.0014463.9642 242
314655.0015654.6821 211 114682.5014682.62JKa KcJKa Kc
Frequency (MHz)Previous Work(MHz)131 231 314753.623025 53025
614765.0014764.7532 230 314823.0014823.2743 241 314863.3020 210
114902.5014903.1354 252 314948.0014947.3365 263 315100.502319 42319
515153.0015153.2076 274 315356.001512 31512 415740.5015740.4788 186
215744.5015743.0187 285 315755.0015755.213630 63630
715933.7815933.9098 296 316346.004235 74235 816834.8216834.511411
31411 416920.502924 52924 616943.002218 42218 516960.50109 2107
317183.594840 84840 917480.381310 31310 417932.0099 197
217992.001110 2118 318322.503529 63529 718403.50Room-Temp Spectrum
of PyridineGround Vibrational StateSpectroscopic ConstantSorensen
work1Ye et al work2Current work*1Current work*2A
(MHz)6039.2446039.24436039.086039.09B
(MHz)5804.9035804.91385804.725804.74C
(MHz)2959.2202959.210012959.182959.19J
(kHz)-0.0111.3897-0.011*1.3897*JK (kHz)-2.252-2.4984-1.18-1.18K
(kHz)1.6951.22781.261.26J (kHz)-0.00704K
(kHz)-2.0074Nlines52118546461G. O. Srensen, J. Molec. Spectr.,
(1967) 22, 325-346.2Enyi Ye, Ryan P.A. Bettens, Frank C. DeLucia,
Douglas T. Petkie, and Sieghard Albert, J. Molec. Spectr., (2005)
232, 61-65.* J values fixed to those of previous work.Room-Temp
Spectrum of PyridineFirst Excited Vibrational State1G. O. Srensen,
J. Molec. Spectr., (1967) 22, 325-346.JKa KcJKa Kc
Frequency (MHz)Previous Work(MHz)1108 2108 311515.5064 264
314153.501613 31613 414708.0020 210 114907.0065 263 315051.501512
31512 415979.131411 31411 417106.002218 42218 517490.101310 31310
418067.001110 2118 318077.00Spectroscopic ConstantYe et al
work2Current workA (MHz)6032.36966032.44B (MHz)5805.20815805.23C
(MHz)2962.29722962.56J (kHz)1.38961.3896*JK (kHz)-2.4936-0.895K
(kHz)1.21691.27J (kHz)-0.0103K (kHz)-2.095Nlines58410* J value
fixed to those of previous work.
Conclusions:Constructed a new, inexpensive room-temperature
chirped-pulse Fourier transform microwave (RT-CP-FTMW)
spectrometer.
Confirmed its frequency accuracy by performing tests on
methanol.
Measured and fit the ground state and first excited vibrational
state of pyridine in the 10-18 GHz region of the spectrum.
Since they shifted and disappeared they were not ghost peaks.
18Future WorkFrequency doubler0 - 500 MHz sweep (instead of 0-250
MHz)More Construction
Acknowledgements:Dr. Steve Shipman (New College of Florida)The
Pate lab (University of Virginia)SCICU (South Carolina Independent
Colleges and Universities) Student/Faculty Research ProgramCoker
College
