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Augustana, March 2, 2007Darin J. Ulness, Concordia College 1Noisy Light Spectroscopy

Noisy LightSpectroscopy:

Putting noise to good use

Darin J. UlnessDepartment of Chemistry

Concordia CollegeMoorhead, MN

TheA

Augustana, March 2, 2007Darin J. Ulness, Concordia College 2Noisy Light Spectroscopy

OutlineI. IntroductionII. Experiment

• Coherent Raman Scattering

III. Hydrogen Bonding• Pyridine systems

IV. Prospectus

Augustana, March 2, 2007Darin J. Ulness, Concordia College 3Noisy Light Spectroscopy

SpectroscopyUsing light to gain information about matter

•Transition frequencies•Lineshapes•Susceptibilities

Information Uses of information•In Chemistry•In Biology•In Engineering

Augustana, March 2, 2007Darin J. Ulness, Concordia College 4Noisy Light Spectroscopy

Light

frequency

Spectrum

time

One frequency (or color)

Electromagnetic radiation•Focus on electric field part

Augustana, March 2, 2007Darin J. Ulness, Concordia College 5Noisy Light Spectroscopy

Noisy Light: Definition•Broadband•Phase incoherent•Quasi continuous wave

Ele

tric

Fie

ld S

tren

gth

Time

Noi

sy L

ight

Spe

ctru

m

Frequency

Time resolution onthe order of the correlation time, c

Augustana, March 2, 2007Darin J. Ulness, Concordia College 6Noisy Light Spectroscopy

Experiment•Coherent Raman Scattering: e.g., CARS•Frequency resolved signals•Spectrograms•Molecular liquids

Augustana, March 2, 2007Darin J. Ulness, Concordia College 7Noisy Light Spectroscopy

Nonlinear Optics

P= ESignal

Material

Light field

Perturbation series approximation

P(t) = P(1) + P(2) + P(3) …

P(1) = (1)E, P(2) = (2)EE, P(3) = (3)EEE

Augustana, March 2, 2007Darin J. Ulness, Concordia College 8Noisy Light Spectroscopy

CARSCoherent Anti-Stokes Raman Scattering

R

1

12

CARS

1-2= R

CARS= 1 +R

Augustana, March 2, 2007Darin J. Ulness, Concordia College 9Noisy Light Spectroscopy

CARS with Noisy Light•I(2)CARS

•We need twin noisy beams B and B’.•We also need a narrowband beam, M.•The frequency of B (B’) and M differ by roughly the Raman frequency of the sample.•The I(2)CARS signal has a frequency that is anti-Stokes shifted from that of the noisy beams.

B

B’M

I(2)CARS

Augustana, March 2, 2007Darin J. Ulness, Concordia College 10Noisy Light Spectroscopy

I(2)CARS: Experiment

Monochromator

NarrowbandSource

BroadbandSource(noisy light)

Lens

Sample

Interferometer

B

B’

MI(2)CARS

ComputerCCD

Augustana, March 2, 2007Darin J. Ulness, Concordia College 11Noisy Light Spectroscopy

I(2)CARS: SpectrogramMonochromator

NarrowbandSource

BroadbandSource

Lens

Sample

Interferometer

B

B’

MI(2)CARS

ComputerCCD

•Signal is dispersed onto the CCD

•Entire Spectrum is taken at each delay

•2D data set: the Spectrogram

Augustana, March 2, 2007Darin J. Ulness, Concordia College 12Noisy Light Spectroscopy

I(2)CARS: Spectrogram

Pixel A

A

Pixel B

B

Pixel C

C

Dark regions: high intensityLight regions: low intensity

Oscillations: downconversion of Raman frequency.Decay: Lineshape function

Augustana, March 2, 2007Darin J. Ulness, Concordia College 13Noisy Light Spectroscopy

SpectrogramNo new information can be extracted.

However…

•Huge oversampling gives much enhanced precision.•Visually appealing presentation of data gives much insight.

Augustana, March 2, 2007Darin J. Ulness, Concordia College 14Noisy Light Spectroscopy

I(2)CARS: Data Processing

18000 18100 18200 18300 18400

-2

-1

0

1

2

BenzeneT22

0 200 400 600 800 1000 1200

0

25

50

75

100

125

150

BenzeneT22

100 200 300 400

0.2

0.4

0.6

0.8

Fourier

Transformation

X-Marginal

Augustana, March 2, 2007Darin J. Ulness, Concordia College 15Noisy Light Spectroscopy

Virtues of I(2)CARS•Less expensive.•Easier experiment to perform.•Signals are more robust.•Immune to dispersion effects. •Exquisitely sensitive to relative changes in the vibrational frequency and dephasing rate constant.

Augustana, March 2, 2007Darin J. Ulness, Concordia College 16Noisy Light Spectroscopy

Hydrogen Bonding•Interaction between a hydrogen atom and oxygen or nitrogen (or fluorine)

•A very weak chemical interaction (bond)

•A very strong physical interaction

•Exploited extensively in biological systems

O, NO, N

O, NO, N

H

Augustana, March 2, 2007Darin J. Ulness, Concordia College 17Noisy Light Spectroscopy

Pyridine Systems

Why Pyridine

•Simple molecule

•Important component in many compounds

•Biological importance

•Strong I(2)CARS signal

•H-bond acceptor but not a H-bond donor.

N

C

C

C

C

C

H H

H

H

H

Augustana, March 2, 2007Darin J. Ulness, Concordia College 18Noisy Light Spectroscopy

Pyridine: Normal Modes

1 990

A1

Ring B

reathing

12 1030

A1

Triangle

Augustana, March 2, 2007Darin J. Ulness, Concordia College 19Noisy Light Spectroscopy

Pyridine and H-bondingNeat Pyridine•Two peaks

With H-bond•Three peaks

Augustana, March 2, 2007Darin J. Ulness, Concordia College 20Noisy Light Spectroscopy

Pyridine and H-bondingKey Results

•Some pyridine is free some is hydrogen bonded

•Hydrogen bonding blue-shifts the ring breathing mode

•Hydrogen bonding does not shift the triangle mode

Augustana, March 2, 2007Darin J. Ulness, Concordia College 21Noisy Light Spectroscopy

Pyridine: Inner Tube Model•Molecular orbitals•Electrostatics•Compare with benzene

•Stabilization through delocalization

•H-bonding makes pyridine more “benzene-like”

Augustana, March 2, 2007Darin J. Ulness, Concordia College 22Noisy Light Spectroscopy

Pyridine: Inner Tube Model

Electron density for Benzene

= +Electron density for free pyridine

Electron density for H-bonded pyridine

= +

Full e- density e- density sp2 e- density

Full e- density e- density sp2 e- density

Augustana, March 2, 2007Darin J. Ulness, Concordia College 23Noisy Light Spectroscopy

Pyridine: Test of ModelVary the strength of hydrogen bonding

Formamide N-H-N bond~ 3-4 Kcal/mol

WaterN-H-O bond~ 6-7 Kcal/mol

Acetic AcidProton transfer (acid/base)

980 990 1000 1010 1020 1030 10400.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

Nor

mal

ized

X m

argi

nal i

nten

sity

Raman wavenumber / cm -1

Formamide

Water

Acetic Acid

4 cm-1

8 cm-1

14 cm-1

Augustana, March 2, 2007Darin J. Ulness, Concordia College 24Noisy Light Spectroscopy

Pyridine: Peak Broadening

Augustana, March 2, 2007Darin J. Ulness, Concordia College 25Noisy Light Spectroscopy

Peak Broadening ModelsNetwork model

Thermalized distribution model

Etc.

Fileti, E.E.; Countinho, K.; Malaspina, T.; Canuto, S. Phys. Rev. E. 2003, 67, 061504.

Augustana, March 2, 2007Darin J. Ulness, Concordia College 26Noisy Light Spectroscopy

Pyridine/water Temperature

980 990 1000 1010 1020 1030 1040

0.0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

T = -40 O

C

T = -20 O

C

T = 0 O

C

T = 20 O

C

T = 40 O

C

T = 60 O

C

Nor

mal

ized

X m

argi

nal i

nten

sity

Raman wavenumber / cm-1

Xpy = 0.55

Augustana, March 2, 2007Darin J. Ulness, Concordia College 27Noisy Light Spectroscopy

Pyridine/water TemperatureXpy = 0.55

-40 -20 0 20 40 60

1.0

1.5

2.0

2.5

3.0

3.5

Pea

k w

idth

(ob

s) /

cm

-1

Temperature / O

C

Hydrogen Bonded Ring Breathing Mode

“Free” Pyridine Ring Breathing Mode

Triangle Mode

Augustana, March 2, 2007Darin J. Ulness, Concordia College 28Noisy Light Spectroscopy

Pyridine/water TemperatureXpy = 0.55

-1

-40 -20 0 20 40 60

988

990

992

994

996

998

1029.5

1030.0

1030.5

1031.0

1031.5

Ram

an W

aven

umbe

r /

cm

Temperature / O

C

Hydrogen Bonded Ring Breathing Mode

“Free” Pyridine Ring Breathing Mode

Triangle Mode

Augustana, March 2, 2007Darin J. Ulness, Concordia College 29Noisy Light Spectroscopy

ProspectusSummary:•Noisy light provides an alternative method for probing ultrafast dynamics of the condensed phase.•Useful tool for probing hydrogen bonding using “test” molecules.•Simple model useful in understanding hydrogen bonding in pyridine.•Thermalized distribution is likely cause of peak broadening.

Augustana, March 2, 2007Darin J. Ulness, Concordia College 30Noisy Light Spectroscopy

ProspectusFuture of noisy light at Concordia:•Other pyridine based molecules

•Hydroxymethyl pyridine.•Halo pyridines.

•Other nitrogen heterocycles.•A principle goal is to develop an I(2)CARS based microscopy.

Augustana, March 2, 2007Darin J. Ulness, Concordia College 31Noisy Light Spectroscopy

AcknowledgementsFormer StudentsJahan Dawlaty: Cornell University, Ph.D. candidate in optical electronics Dan Biebighauser: Vanderbilt University, Ph.D. in mathematicsJohn Gregiore: Cornell University, Ph.D. candidate in physicsDuffy Turner: MIT, Ph.D. candidate in physical chemistryPye Phyo Aung: John’s Hopkins University, Ph.D. candidate in mathematicsTanner Schulz: University of Minnesota, Ph.D. candidate in physicsLindsay Weisel: Michigan State University, Ph.D. candidate in physical chemistry

Current StudentsBritt BergerZach JohnsonErik BergDanny GreenSarah Freeman

Other Group MembersDr. Mark Gealy, Department of PhysicsDr. Eric Booth, Post-doctoral researcher

FundingNSF CAREER Grant CHE-0341087Henry Dreyfus Teacher/Scholar programConcordia Chemistry Research Fund

Augustana, March 2, 2007Darin J. Ulness, Concordia College Noisy Light Spectroscopy

Augustana, March 2, 2007Darin J. Ulness, Concordia College 23Noisy Light Spectroscopy

Pyridine and Water

960 970 980 990 1000 1010 1020 1030 1040

0.0

0.2

0.4

0.6

0.8

1.0 Pyridine/water solution: X(py)=0.6

T = -4o

T = 3o

T = 23o

T = 32o

T = 42o

T = 52o

T = 62o

T = 72o

T = 76o

No

rma

lize

d X

-ma

rgin

al

Wavenumber / cm-1

Augustana, March 2, 2007Darin J. Ulness, Concordia College 7Noisy Light Spectroscopy

Noisy Light: Alternative•Its cw nature allows precise measurement of transition frequencies.•Its ultrashort noise correlation time offers femtosecond scale time resolution.•It offers a different way to study the lineshaping function.•It is particularly useful for coherent Raman scattering.•Other spectroscopies: photon echo, OKE, FROG, polarization beats…

Augustana, March 2, 2007Darin J. Ulness, Concordia College 8Noisy Light Spectroscopy

Theory

Optical coherence theory

Perturbation theory: Density operator

Noisy Light Spectroscopy

Augustana, March 2, 2007Darin J. Ulness, Concordia College 9Noisy Light Spectroscopy

Theoretical Challenges•Complicated Mathematics•Complicated Physical Interpretation

Difficulty•The cw nature requires all field action permutations. The light is always on.•The proper treatment of the noise cross-correlates chromophores.

Solution•Factorized time correlation (FTC) diagram analysis

Augustana, March 2, 2007Darin J. Ulness, Concordia College 10Noisy Light Spectroscopy

FTC Diagram Analysis

Set of intensity level terms

(pre-evaluated)

Set of evaluated intensity level

terms

Messy integration and algebra

Set of FTC diagrams

ConstructionRules

EvaluationRules

Physicshard hard

easy

Augustana, March 2, 2007Darin J. Ulness, Concordia College A1Noisy Light Spectroscopy

Utility of FTC Diagrams•Organize lengthy calculations•Error checking•Identification of important terms•Immediate information of about features of spectrograms•Much physical insight that transcends the choice of mathematical model.

Augustana, March 2, 2007Darin J. Ulness, Concordia College A2Noisy Light Spectroscopy

Example: I(2)CARS

P(t,{ti})

P(s,{si})

arrow segments: B, B’ correlation

-dependentline segments: B, B or B’,B’ correlation

-independent

FTC analysis•Each diagram with arrows has a topologically equivalent partner diagram containing only lines: 2:1 dynamic range•Each diagram with arrows has a topologically equivalent partner diagram that has arrows pointing in the opposite direction: signal must be symmetric in

Augustana, March 2, 2007Darin J. Ulness, Concordia College 4Noisy Light Spectroscopy

Modern SpectroscopyFrequency Domain•Measure Spectra•Examples

•IR, UV-VIS, Raman•Material response

•Spectrally narrow•Temporally slow

Time Domain•Response to light pulse•Examples

•PE, transient abs.•Material response

•Spectrally broad•Temporally fast

Augustana, March 2, 2007Darin J. Ulness, Concordia College 4Noisy Light Spectroscopy

Modern SpectroscopyFrequency Domain•Measure Spectra•Examples

•IR, UV-VIS, Raman•Material response

•Spectrally narrow•Temporally slow

Time Domain•Response to light pulse•Examples

•PE, transient abs.•Material response

•Spectrally broad•Temporally fast

Augustana, March 2, 2007Darin J. Ulness, Concordia College 4Noisy Light Spectroscopy

Modern SpectroscopyFrequency Domain•Measure Spectra•Examples

•IR, UV-VIS, Raman•Material response

•Spectrally narrow•Temporally slow

Time Domain•Response to light pulse•Examples

•PE, transient abs.•Material response

•Spectrally broad•Temporally fast

Is there another useful technique?Noisy light? YES!

Augustana, March 2, 2007Darin J. Ulness, Concordia College A3Noisy Light Spectroscopy

Example: I(2)CARS

Pixel A

A

Pixel B

B

Pixel C

C

The I(2)CARS data shows • 2:1 dynamics range• symmetry

Augustana, March 2, 2007Darin J. Ulness, Concordia College A4Noisy Light Spectroscopy

0 1 2 3 4 50.00

0.05

0.10

0.15

0.20

0.25

0.30

s

S/N

(a)

0 1 2 3 4 50.00

0.05

0.10

0.15

0.20

0.25

0s

D

S/N

(b)

Augustana, March 2, 2007Darin J. Ulness, Concordia College A5Noisy Light Spectroscopy

Augustana, March 2, 2007Darin J. Ulness, Concordia College A6Noisy Light Spectroscopy

Augustana, March 2, 2007Darin J. Ulness, Concordia College A7Noisy Light Spectroscopy

-20 0 20 40 60 800.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

Fit Results:ratio =0.00783 T + 0.905R = 0.9942

Fre

e p

yr.

to

H-b

ou

nd

pyr

Temperature (Co)

- ∆G° Product Favored

- ∆H° Exothermic

- ∆S° Entropically unfavorable

Augustana, March 2, 2007Darin J. Ulness, Concordia College A8Noisy Light Spectroscopy

17300 17400 17500 17600

-400

-200

0

200

400

pyridine with .4g AgNO3

960 970 980 990 1000 1010 1020 1030 1040-0.2

0.0

0.2

0.4

0.6

0.8

1.0Pyridine / AgNO

3

g AgNO3/ml py 0.00 0.061 0.097 0.121 0.170 0.238 0.298 0.341 0.409

No

rma

lize

d X

-ma

rgin

al

Wavenumber / cm-1

0.00 0.05 0.10 0.15 0.20 0.25-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4 Pyridine/AgNO3

Ratio

27.1 Xeff

2 -.97 X

eff + 0.013

Co

mp

lexe

d p

yri

din

e t

o

Fre

e p

yri

din

ed

Effective mole fraction AgNO3

complex = Icomplex

free xfree

Icomplex = Ifree at 0.21 mole fraction

complex = 1

free .79

complex = 3.76

free

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