Novel Applications of a Shape Sensitive Detector 2: Double Resonance Amanda Shirar Purdue University Molecular Spectroscopy Symposium June 19, 2008

Searching For “Dark States” Traditional problems Transition moment not allowed for laser based methods Using Microwave Spectroscopy Shape Sensitive Only need a permanent dipole moment Cavity Broadband

Intermediate state S0S0 S1S1 T1T1 ISC Excited State Reaction Dynamics MW Probe Products Structural Information of meta-stable intermediate species Excited state reaction pathways Barrier heights of singlet state o-Methylbenzaldehyde

W W 0 0 W W 0 0 Intensity (Arb. Units) First Coupling Scheme Second Coupling Scheme 2-D Dynamic Rotational Spectroscopy: 50 ns 10 ns 20 ns 30 ns 40 ns 50 ns 10 ns 20 ns 30 ns 40 ns Intensity (Arb. Units)

General Setup UV Laser Cavity Broadband Laser Bandwidth: ~0.4cm -1 Laser Power: mJ ( nm)

Aniline ‡ J.L. Knee, P.M. Johnson, J Chem Phys. 1 (1984) 13. * D.G. Lister, J.K. Tyler, J.H. Hog, N.W. Larsen, J Mol Spec. 23 (1974) 253. Dipole Moment D* Triplet Lifetime  s ‡ At the origin Excited State Dynamics Intersystem Crossing

Steps to Acquire Excited State Spectra 1) Ground State Microwave Spectrum (CP-FTMW) 2) Monitor Single Molecular Transition while scanning the laser (Cavity) 3) Monitor Many Molecular Transitions while scanning the laser (CP-FTMW)

Steps to Acquire Excited State Spectra 1) Ground State Microwave Spectrum (CP-FTMW) 2) Monitor Single Molecular Transition while scanning the laser (Cavity) 3) Monitor Many Molecular Transitions while scanning the laser (CP-FTMW)

Ground State Spectrum D.G. Lister, J.K. Tyler, J.H. Hog, N.W. Larsen, J Mol Spec. 23 (1974) 253. Ground State Rotational Spectrum Rotational Constants A = MHz B = MHz C = MHz  J 1  2

Steps to Acquire Excited State Spectra 1) Ground State Microwave Spectrum (CP-FTMW) 2) Monitor Single Molecular Transition while scanning the laser (Cavity) 3) Monitor Many Molecular Transitions while scanning the laser (CP-FTMW)

Ground State Depletion J Ex J=2 J=1 Excitation Source (Laser) Monitor S 0 Rotational Transitions Frequency Domain Ground State Depletion Time Domain Ground State Depletion MW Probe 00 (~50ns) Laser Pump  Monitor Ground State (S 0 ) Rotational Transitions  Signal Level Proportional to Population Difference of Rotational Levels (  N)  Population removed from upper rotational level increases  N; Increases Signal  Population removed from lower rotational level decreases  N; Decreases Signal  Laser Resolution ~ 0.4 cm -1 (~1.2 GHz)  Greatly Simplifies Assignment  Absorption-like Measurement

Different Vibronic Bands Origin 6a a a 0 1 Monitoring Transition At GHz

Band Contour at the Origin S 0 ‡ S1*S1* A (MHz) B (MHz) C (MHz) ‡ D.G. Lister et al., J Mol Spec. 23 (1974) 253. * E.R. Kerstel et al. J Mol Spec. 177 (1996) 74. H.M. Pickett, J Mol Spec. 148 (1991) 371. B-type Band Contour

LIF vs GSD LIF GSD Origin Transition

Steps to Acquire Excited State Spectra 1) Ground State Microwave Spectrum (CP-FTMW) 2) Monitor Single Molecular Transition while scanning the laser (Cavity) 3) Monitor Many Molecular Transitions while scanning the laser (CP-FTMW)

Multiplex Laser Wavenumber (cm -1 ) Microwave Frequency (MHz) 1 01       3 12 Depletion Gain Ground State Spectrum GSD Scan

Conclusions CP-FTMW used to record Ground State Rotational Spectrum. Used the cavity setup to acquire GSD of single molecular transition ( ). CP-FTMW GSD of multiple transitions at once. Future Research Looking for Dark Electronic States (T 1 )

Acknowledgements Funding Dr. Henry & Camille Dreyfus Foundation - Young Faculty Scholar Dr. Brian Dian Dr. Chandana Karunatilaka Fellow Graduate Students Kelly Hotopp Giana Storck Undergraduates Erin Biddle

Chamber PLDRO (18.9 GHz) PLDRO (13 GHz) Power Supply (P.S.) 12 GHz Scope 13 GHz Filter Arb D8 Analog Waveguide D1 D2 Trig In BNC In Out Quartz Osc. Ref In SMA RF Clock Input Rb Clock 10 MHz Insulated MW Ch 3 Ch 2 Marker MHz Scope GPIB RS232 COM1 USB DG535 Trigger Laser Power Supply Q-SwitchLamp D6D5 Wavemeter Frequency Conversion Unit Dye Laser RS232 Ext Ref In RF IF LO IF RF To P.S. 200W To P.S. 100 MHz To P.S. 50  Circuit To Switch To Amp To 18.9 GHz To 13 GHz To Quartz Oscillator Masterclock

Excited State Spectrum J Ex1 J=2 J=1 Excitation Source (Laser) Monitor S 1 Rotational Transitions Frequency Domain Excited State Spectrum Time Domain Excited State Spectrum MW Probe 00 (Fixed) Laser Pump  Set laser to specific vibronic mode  Determine molecular structure of excited state  Calculate the lifetime of excited state species  Only need a dipole moment to observe a spectra  Shorter microwave pulse (~250 ns) J Ex2 Detector

18.9 GHz PDRO 13 GHz PDRO 12 GHz Oscilloscope (40 Gs/s) 13 GHz Filter 200W 50  Circuit Arbitrary Waveform Generator 100 MHz Quartz Oscillator GHz Chirped Pulse GHz 8-18 GHz Pulsed Sample Nozzle GHz GHz 1) 2) 3) Free Induction Decay 13 GHz Simplified Circuit

18.9 GHz PDRO 12 GHz Oscilloscope (40 Gs/s) 200W Arbitrary Waveform Generator 100 MHz Quartz Oscillator GHz Chirped Pulse 8-18 GHz Pulsed Sample Nozzle GHz GHz 1) 2) 3) Free Induction Decay Microwave Circuit General Simplified Circuit 50  Circuit

Chamber PLDRO (18.9 GHz) PLDRO (13 GHz) Power Supply (P.S.) 12 GHz Scope 13 GHz Filter Arb D8 Analog Waveguide Pulsed Valve Driver D3 D1 D2 Trig In Ext Trig BNC In Out Quartz Osc. Ref In SMA RF Clock Input Rb Clock 10 MHz Insulated MW Ch 3 Ch 2 Marker MHz Scope GPIB RS232 COM1 USB DG535 Trigger Laser Power Supply Q-SwitchLamp D6D5 Wavemeter Frequency Conversion Unit Dye Laser RS232 Ext Ref In RF IF LO IF RF To P.S. 200W To P.S. 100 MHz To P.S. 50  Circuit To Switch To Amp To 18.9 GHz To 13 GHz To Quartz Oscillator D7 Discharge Experiment Masterclock

Cavity Setup MW Synthesizer Arb 12GHz Scope 50/ MHz 30 MHz +  30 MHz +  Generate Microwave frequency Cavity Mixing Signal Detection - Molecular Frequency  - Frequency Shift

Broadband Setup 4x

Band with Relative cm-1