AUSTIN L. MCJUNKINS, K. MICHELLE THOMAS, APRIL RUTHVEN, AND GORDON G. BROWN Department of Science and Mathematics, Coker College, 300 E College Ave., Hartsville, SC MH10 ROOM-TEMPERATURE CHIRPED-PULSE FOURIER TRANSFORM MICROWAVE (RT-CP-FTMW) SPECTRUM OF PYRIDINE

Outline  Inexpensive 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 labs Inexpensive Room-Temperature Chirped-Pulse Fourier transform (RT-CP-FTMW) Microwave Spectrometer

MW Synthesizer ν0ν0 Fourier Transform Oscilloscope (1 GHz) Chirped-Pulse Arbitrary Function Generator (240 MHz) molecular FID static cell (12 feet of WRD-750 waveguide) to vacuum mixer power divider amplifier Diode limiter 1 S. T. Shipman, J. L. Neill, B. Kroncke, B. H. Pate, and P. Groner, Presentation at the International Symposium on Molecular Spectroscopy, Columbus, OH, USA, Z. 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, ~480 MHz chirped pulse 1W solid- state amp Inexpensive Room-Temperature Chirped-Pulse Fourier transform (RT-CP-FTMW) Microwave Spectrometer

MW Synthesizer ν0ν0 Fourier Transform Oscilloscope (1 GHz) Chirped-Pulse Arbitrary Function Generator (240 MHz) molecular FID static 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, ~480 MHz chirped pulse 1W solid- state amp double sideband mixer* diode limiter Advanced Control Components ACLM- 4619FC36 Inexpensive Room-Temperature Chirped-Pulse Fourier transform (RT-CP-FTMW) Microwave Spectrometer

240 MHz Chirped Pulse before power amplifier

Our spectrometer

Outline  Inexpensive 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 2 02 – ( MHz) (on cheap oscilloscope)

Benchmark: Methanol v 0 = 12300MHz white spectrum v 0 = MHz gold spectrum For : – = MHz – = MHz

Benchmark: Methanol Assignment Previous Observation (MHz) 2 Shipman et al observation (MHz) 1 Current Work (MHz) – – S. T. Shipman, J. L. Neill, B. Kroncke, B. H. Pate, and P. Groner, Presentation at the International Symposium on Molecular Spectroscopy, Columbus, OH, USA, L. H. Xu and F. J. Lovas, J. Phys. Chem. Ref. Data, 1997, 26, 17.

Outline  Inexpensive room-temperature chirped- pulse Fourier transform (RT-CP-FTMW) microwave spectrometer  Benchmark test - methanol  Room-Temperature spectrum of pyridine

Previous MW work on Pyridine 1,2  G. O. Sørensen: MW spectrum 8.5 – ºC and -20 ºC 1 Ground vibrational state Quadrupole Coupling Constants  Ye et al.: 75 – 110 GHz and 260 – 370 GHz Improved constants for ground state Assigned 6 vibrationally excited states 1 G. O. Sørensen, J. Molec. Spectr., (1967) 22, Enyi Ye, Ryan P.A. Bettens, Frank C. DeLucia, Douglas T. Petkie, and Sieghard Albert, J. Molec. Spectr., (2005) 232,

Room-Temp Spectrum of Pyridine 1,2 10,000 averages; ~5 mTorr; 25 ºC ~ 10 sec/step, 35 (overlapping) steps

Room-Temp Spectrum of Pyridine Ground Vibrational State 1 G. O. Sørensen, J. Molec. Spectr., (1967) 22, J” Ka” Kc” J’ Ka’ Kc’ Frequency (MHz) Previous Work(MHz) J” Ka” Kc” J’ Ka’ Kc’ Frequency (MHz) Previous Work(MHz)

Room-Temp Spectrum of Pyridine Ground Vibrational State Spectroscopic Constant Sorensen work 1 Ye et al work 2 Current work* 1 Current work* 2 A (MHz) B (MHz) C (MHz) Δ J (kHz) *1.3897* Δ JK (kHz) Δ K (kHz) δ J (kHz) δ K (kHz) N lines G. O. Sørensen, J. Molec. Spectr., (1967) 22, Enyi Ye, Ryan P.A. Bettens, Frank C. DeLucia, Douglas T. Petkie, and Sieghard Albert, J. Molec. Spectr., (2005) 232, * Δ J values fixed to those of previous work.

Room-Temp Spectrum of Pyridine First Excited Vibrational State 1 G. O. Sørensen, J. Molec. Spectr., (1967) 22, J” Ka” Kc” J’ Ka’ Kc’ Frequency (MHz) Previous Work(MHz) Spectroscopic Constant Ye et al work 2 Current work A (MHz) B (MHz) C (MHz) Δ J (kHz) * Δ JK (kHz) Δ K (kHz) δ J (kHz) δ K (kHz) N lines * Δ 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 GHz region of the spectrum.

Future Work  Frequency doubler MHz sweep (instead of 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 Program  Coker College