Novel Applications of a Shape Sensitive Detector 2: Double

Resonance

Amanda ShirarPurdue 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

Intermediatestate

S0

S1

T1

ISCISC

Excited StateReaction Dynamics

MW Probe Products

Structural Information of meta-stable intermediate

species

Excited state reaction pathways

Barrier heights of singlet stateo-Methylbenzaldehyde

W

W

0

0

3W

3W

Intensity (Arb. Units)

1800016000140001200010000Frequency (MHz)

W

W

0

0 3W

3W

Intensity (mV)

1800016000140001200010000Frequency (MHz)

Inte

nsi

ty (

Arb

. U

nit

s)First Coupling

Scheme

Second CouplingScheme

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

Inte

nsi

ty (

Arb

. U

nit

s)

General Setup

UV Laser

CavityBroadband

Laser Bandwidth: ~0.4cm-1

Laser Power: 20-35 mJ (420-270 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 Moment1.129 D*

Triplet Lifetime5.653 s‡

At the origin

Excited State DynamicsIntersystem 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 Spectrum202-303212-313

211-312

D.G. Lister, J.K. Tyler, J.H. Hog, N.W. Larsen, J Mol Spec. 23 (1974) 253.

Ground State Rotational Spectrum

Rotational ConstantsA = 5617.40 MHzB = 2593.83 MHzC = 1777.04 MHz

J 12

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

JEx

J=2

J=1

Excitation Source(Laser)

Monitor S0 Rotational Transitions

Frequency DomainGround State Depletion

Time DomainGround State Depletion

MW

P

rob

e

0

(~50ns)Las

er

Pu

mp

Monitor Ground State (S0) 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

6a01 10

1

1201

6a02

1016a0

1

Monitoring202-303

TransitionAt 12.563 GHz

Band Contour at the Origin

S0 ‡ S1

*

A (MHz) 5617.4 5285.1

B (MHz) 2593.8 2633.5

C (MHz) 1777.0 1759.2

‡ 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 LIFGSD

Origin

202-303 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

Lase

r W

aven

um

ber

(cm

-1)

Microwave Frequency (MHz)

101202

111212

110211

212313

202303

211312

DepletionGain

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 (202-303).

CP-FTMW GSD of multiple transitions at once.

Future Research Looking for Dark Electronic States (T1)

Acknowledgements

FundingDr. 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 GHzFilter

ArbD8Analog

Waveguide

D1 D2

Trig In

BNC

In Out

Quartz Osc.

Ref In

SMA

RF Clock Input

Rb Clock

10 MHz

10 MHz

Insulated MW

Ch 3

Ch 2

Marker 1 500 MHz Scope

GPIB

GPIB

RS232

COM1

USB

DG535

Trigger

Laser Power Supply

Q-Switch Lamp

D6 D5

Wavemeter

Frequency Conversion

Unit

Dye Laser

RS232

RS232

Ext Ref In

RFIF

LO

LOIF

RF

To P.S.To P.S.

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

JEx1

J=2

J=1

Excitation Source(Laser)

Monitor S1 Rotational Transitions

Frequency DomainExcited State Spectrum

Time DomainExcited State Spectrum

MW

P

rob

e

0

(Fixed)Las

er

Pu

mp

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)

JEx2D

etec

tor

18.9 GHzPDRO

13 GHz PDRO

12 GHz Oscilloscope

(40 Gs/s)

13 GHzFilter

200W

50 Circuit

ArbitraryWaveformGenerator

100 MHz Quartz Oscillator

GHz Chirped Pulse0.1-5 GHz

8-18 GHz

Pulsed SampleNozzle

0.9-10.9 GHz26.9-36.9 GHz

1)

2)

3)

Free InductionDecay

13 GHz Simplified Circuit

18.9 GHzPDRO

12 GHz Oscilloscope

(40 Gs/s)

200W

ArbitraryWaveformGenerator

100 MHz Quartz Oscillator

GHz Chirped Pulse

8-18 GHzPulsed SampleNozzle

0.9-10.9 GHz26.9-36.9 GHz

1)

2)

3)

Free InductionDecay

MicrowaveCircuit

General Simplified Circuit

50 Circuit

Chamber

PLDRO (18.9 GHz)

PLDRO(13 GHz)

Power Supply(P.S.)

12 GHz Scope

13 GHzFilter

ArbD8Analog

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

10 MHz

Insulated MW

Ch 3

Ch 2

Marker 1 500 MHz Scope

GPIB

GPIB

RS232

COM1

USB

DG535

Trigger

Laser Power Supply

Q-Switch Lamp

D6 D5

Wavemeter

Frequency Conversion

Unit

Dye Laser

RS232

RS232

Ext Ref In

RFIF

LO

LOIF

RF

To P.S.To P.S.

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

12GHzScope

50/50

+ 30 MHz

30 MHz

+

30 MHz

+

Generate Microwave frequency

Cavity

MixingSignal

Detection

- Molecular Frequency - Frequency Shift

Broadband Setup

4x

Band with Relative cm-1