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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