augustana, march 2, 2007darin j. ulness, concordia college 1 noisy light spectroscopy noisy light...

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


OutlineI. IntroductionII. Experiment

• Coherent Raman Scattering

III. Hydrogen Bonding• Pyridine systems

IV. Prospectus


SpectroscopyUsing light to gain information about matter

•Transition frequencies•Lineshapes•Susceptibilities

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


Light

frequency

Spectrum

time

One frequency (or color)

Electromagnetic radiation•Focus on electric field part


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


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


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


CARSCoherent Anti-Stokes Raman Scattering

R

1

12

CARS

1-2= R

CARS= 1 +R


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


I(2)CARS: Experiment

Monochromator

NarrowbandSource

BroadbandSource(noisy light)

Lens

Sample

Interferometer

B

B’

MI(2)CARS

ComputerCCD


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


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


SpectrogramNo new information can be extracted.

However…

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


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


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.


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


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


Pyridine: Normal Modes

1 990

A1

Ring B

reathing

12 1030

A1

Triangle


Pyridine and H-bondingNeat Pyridine•Two peaks

With H-bond•Three peaks


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


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

•Stabilization through delocalization

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


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

≈


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


Pyridine: Peak Broadening


Peak Broadening ModelsNetwork model

Thermalized distribution model

Etc.

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


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


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


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


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.


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.


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


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


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…


Theory

Optical coherence theory

Perturbation theory: Density operator

Noisy 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


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.


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


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


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!


Example: I(2)CARS

Pixel A

A

Pixel B

B

Pixel C

C

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


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)


-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


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

augustana, march 2, 2007darin j. ulness, concordia college 1 noisy light spectroscopy noisy light...

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