Darin J. Ulness
Department of Chemistry
Concordia College, Moorhead, MN

Spectroscopy
Using light to gain information about matter
Information
• Spectra
• Transition frequencies
• Time dynamics
• Absorptivities
• Susceptibilities
Uses of information
• In Chemistry
• In Biology
• In Engineering

Modern Spectroscopy
Frequency 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 Spectroscopy
Frequency 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

Time Domain Spectroscopy
Ultrashort pulses are used to excite a molecule

Time Domain Spectroscopy
Ultrashort pulses are used to excite a molecule

Creating Ultrashort Pulses
Fourier Transforms!
• Things that happen fast in time require a broad frequency spectrum
• To make a short pulse you need a lot of colors

Phase Locking
Synchronize the phase of the electric field
• Many colors conspire to create a short pulse
• The phases of the different colors need to be “locked”

Noisy light Spectroscopy
Unlock the phase!
• The phases of the different colors have a random relation to one another
• Many colors conspire to create a short pulse coherence time
Frequency
Time

Noisy light Spectroscopy
Interacting with molecules
• The noisy light is “always on” …it is quasi-continuous wave
• The field may interact with the molecule at any time

Foundations of Noisy Light
Noisy Light Spectroscopy
Optical coherence theory
Perturbation theory:
Density operator

Nonlinear Spectroscopy
Signal
Material
P= c
E Light field
Perturbation series approximation
P(t) = P (1) + P (2) + P (3) …
P (1) =
P (3) = c
(1) E, P (2) = c
(2) EE, c
(3) EEE

CARS
C oherent A ntiS tokes R aman S cattering w
R w
1 w
2 w
1 w
CARS w
1
w
2
= w
R w
CARS
= w
1
+ w
R

Bichromophoric Model
(3)
P
( t ) a
Noisy light b
(3) *
P ( s )
< >

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.

New Viewpoint: The c
(5) Story

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.

FTC Diagram Analysis
Messy integration and algebra
Set of intensity level terms
(pre-evaluated)
Construction
Rules
Set of FTC diagrams
Evaluation
Rules Set of evaluated intensity level terms easy hard hard
Physics

FTC Diagram Analysis a b
P ( t ,{ t i
})
P ( s ,{ s i
}) arrow segments : t
-dependent line segments : correlation t
-independent correlation

I (2) CARS
Computer
Monochromator
CCD
Sample
Interferometer t
B’
B
I (2) CARS
Lens
M
Narrowband
Source
Broadband
Source
• Signal is dispersed onto the CCD
• Entire Spectrum is taken at each delay
• 2D data set: the Spectrogram

-1
-2
2
1
0
18000
0.8
I (2) CARS: Data Processing
BenzeneT22
BenzeneT22
150
18100 18200 18300 18400
200
125
Fourier
100
Transformation
50
75
25
0
0 200 400 600 800 1000 1200
300 400 100
0.6
0.4
0.2
X-Marginal

-200
-400
400
200
0
I (2) CARS: Hydrogen Bonding
Pyridine Pyridine
Neat
Pyridine
400
200
0
FT
-200
-400
17300 17400 17500 17600 17300 17400 17500 ave x .45 pyr_water
400
Pyridine/
Water
X w
= 0.55
200
-200
0
-400
17300 17400 17500 17600
17600

I (2) CARS: Hydrogen Bonding

I (2) CARS: Halogen Bonding
2.5
3
3.5
4
1.5
0.5
1
2
0
900 920 940 960
Pyridine and C3F7I
980 1000
Frequency (cm-1)
1020 1040 1060 1080 1100
0.9
Neat
0.3
0.4
0.5
0.6
0.1
0.2
0.7
0.8
C6F13I and Pyridine
3.5
4
2.5
3
1.5
2
0.5
1
0
900 920 940 960 980 1000
Frequency (cm-1)
1020 1040 1060 1080 1100
0.6
0.7
0.4
0.5
.8
0.9
0.2
0.3
Neat
0.1

Halogen Bonding
Electropositve s
-hole
Test Charge
Electronegative
“belt”
Electroneutral
“ring”

Photosynthesis

Acknowledgements
Students
Theory
Jahan Dawlaty
Dan Biebighauser
John Gregiore
Duffy Turner
Kurt Haag
Issac Heath
Carena Daniels
Method Development
Pye Phyo Aung
Tanner Schulz
Lindsay Weisel
Krista Cosert
Perrie Cole
Alex Harsh
Britt Berger
Zach Johnson
Thao Ta Funding
NSF CAREER Grant CHE-0341087
Henry Dreyfus Teacher/Scholar program
Concordia Chemistry Research Fund
Hydrogen/Halogen bonding
Eric Berg
Jeff Eliason
Diane Moliva
Jason Olson
Scott Flancher
Danny Green
Photosynthesis
Becca Hendrickson
Meghan Knudtzon
Dylan Howie
Bobby Spoja
Other Group Members
Dr. Mark Gealy, Department of Physics
Dr. Eric Booth, Post-doctoral researcher
Dr. Haiyan Fan, Post-doctoral researcher