OSU 06/19/08 Ultrabroadband Rotational Spectroscopy: Novel Applications of a Shape Sensitive Detector BRIAN C. DIAN Purdue University Department of Chemistry 560 Oval Dr, West Lafayette, IN Chandana Karunatilaka Post-Doc Amanda Shirar Graduate Student Giana Storck Graduate Student Kelly Hotopp Graduate Student Erin Blaze Biddle Undergraduate Ricky Crawley Jr. Undergraduate

OSU 06/19/08 Why 2D? Ground State Applications –Molecules with many conformers –Low barrier torsional motion Toluene –Biomolecules Excited State Dynamics –Dynamic Rotational Spectroscopy Assigning molecular Eigenstates Rotational Spectroscopic Analogs of 2D NMR Built upon work from Vogelsanger et. al., CPL (1988) v.144, 2, p. 180.

OSU 06/19/ GHz PDRO 12 GHz Oscilloscope (40 Gs/s) 200W Arbitrary Waveform Generator 100 MHz Quartz Oscillator GHz Chirped Pulse GHz 8-18 GHz Pulsed Sample Nozzle GHz GHz 1) 2) Interaction 3) Free Induction Decay How Do we Do This? Condensed Circuit Diagram 20 dB 13.0 GHz PDRO

OSU 06/19/ GHz PDRO 12 GHz Oscilloscope (40 Gs/s) 200W Arbitrary Waveform Generator 100 MHz Quartz Oscillator Pulsed Sample Nozzle GHz GHz 1) 2) Interaction 3) Free Induction Decay x4 20 dB How Do we Do This? Condensed Circuit Diagram GHz Chirped Pulse GHz GHz

OSU 06/19/ GHz PDRO 12 GHz Oscilloscope (40 Gs/s) 200W Arbitrary Waveform Generator 100 MHz Quartz Oscillator Pulsed Sample Nozzle GHz GHz 1) 2) 3) Detection Free Induction Decay x4 20 dB How Do we Do This? Condensed Circuit Diagram GHz Chirped Pulse GHz

OSU 06/19/08  Asymmetric rotor  ~ 20000:1 signal-to-noise across entire Bandwidth  Lines split by nuclear hyperfine of Cl  FWHM Linewidth 65 kHz 20  s gate   b ~ 1.2 Debye Ground State Spectrum of 1-Chloro-1-FluoroEthylene

OSU 06/19/08 Development of 2-D Rotational Spectroscopy - Experimental Design (NMR Analogs) Autocorrelation Spectra - Non-Selective Excitation - Pump all conformers - Probe all conformers - Complex interpretation of time domain spectrum J=0 J=2 J=1 Frequency Domain Energy Level Scheme MW Probe Excitation Source Time Domain Selective Excitation pump probe 11 (Scan) - Pump/Probe pulses nsec long -  1 varied from 2-.1 nsec - Magnitude FT taken in two dimensions

OSU 06/19/08 Time Domain Selective Excitation pump 11 probe (Scan) 0 00 N= ns N=2.5 N=0.5 N=1.5 Selection Rules  N = 1 Energy Level Scheme Ground State 2D Rotational Autocorrelation Spectra A C B

OSU 06/19/08 Ground State 2D Rotational Autocorrelation Spectra Time Domain Selective Excitation pump 11 probe (Scan) 0 00 N= ns F=2.5 F=0.5 F=1.5 Selection Rules  F = 1 Energy Level Scheme

OSU 06/19/08 Ground State Spectrum of 1-chloro-1-flouroethylene

OSU 06/19/08 Data Work Up Issues : - 20  s x 20  s digitization at 40 Gs/s 1.6x10 11 data points (after FT) - S/N Increases a digitization gets longer: Want to digitize as long as possible (w/in limitations of experimental T 2 ) - Significantly reduce points in first dimension by taking ‘cuts’ of the spectral region of interest only - Increases digitization in 2 nd Dimension - Workable solution to < 2 million data points (about what most current desktop applications can handle.)

OSU 06/19/08 Experimental Solution -Experimental Design (NMR Analogs) - Only consider single “connected” hyperfine peaks across four J levels - Selective Excitation - Fold Quantum Resonances onto “carrier” pulse - Digitize at full sampling rate to ‘unwrap’ folded signal - Full broadband results are projected onto a single hyperfine clump J=0 00 J=2 02 J=1 11 Frequency Domain Energy Level Scheme Carrier Frequency - Pump/Probe pulses 100 nsec long -  psec step size - Magnitude FT taken in two dimensions J=2 11 11 (Scan) Pump Project F=1.5 F=2.5 F=3.5

OSU 06/19/08 Broadband 2D Spectra  >1.2 million data points represented in graph  4  s digitization at 40 Gs/s along x-axis  1600 ns digitization at 10 Gs/s along y-axis

OSU 06/19/08 Broadband 2D 0 00  1 11 Spectral Region

OSU 06/19/08 Broadband 2D 2 02  2 11 Spectral Region

OSU 06/19/08 Conclusions Full broadband is not quite ready for prime time. Experimentally worked around by projecting on a single carrier frequency. Theoretically any number of peaks can be projected onto the carrier as long as they are connected to the carrier. Bandwidths of 500MHz (possibly up to 1 GHz) are realizable. Good news! Increases in digital memory are occurring rapidly!

OSU 06/19/08 Acknowledgements Funding: Purdue University Camille and Henry Dreyfus Young Faculty Award Chandana Karunatilaka: Post-Doc Amanda Shirar: Graduate Student Giana Storck: Graduate Student Kelly Hotopp: Graduate Student Erin Blaze Biddle : Undergraduate Ricky Crawley Jr.: Undergraduate Students:

OSU 06/19/08 FROG: 1 ns Sinc Pulse