HIGH-RESOLUTION COHERENT THREE-DIMENSIONAL SPECTROSCOPY OF IODINE 

ZURI HOUSE, PETER C. CHEN, THRESA A. WELLS

SPELMAN COLLEGE, ATLANTA GA

BENJAMIN R. STRANGFELD

GEORGIA INSTITUTE OF TECHNOLOGY, ATLANTA GA

OUTLINE/PURPOSE

• Background

• Experimental Set-up

• Four Wave Mixing Processes

• Data Analysis

• Next Step

• Conclusion

• Acknowledgements

• Purpose of Experiment: To explore and test a new 3 dimensional technique on Iodine

BACKGROUND- IODINE• Purpose of the study

• Understand how 3D spectroscopy can be used for molecules without known spectroscopic constants

• Establish a standard procedure for analyzing unknown molecules

• Reasons for choosing iodine

• Energy levels for two states involved are known and thoroughly studied (X to B transition)

• Simple diatomic molecule with no isotopomers• Used low resolution absorption spectrum to determine

roughly where to set laser

ELECTRONIC SPECTRA

BACKGROUNDTypes of Spectroscopic Methods

• Raman, IR, UV-Vis, NMR (a few examples)

Characteristics of Techniques (in heavily congested systems)

• 1D- highly congested 2D- less congested

• 3D- even less congested, and selective (see next slide)*2D and especially 3D techniques are new and innovative

. .

λaλa

λbI

DATA ANALYSIS- ORIGINAL RUN

RESONANCE• 3D spectroscopy is a fully resonant process

• When 3 beams are resonant with the levels in the molecule, a lot of light is generated and the peaks are more intense

• triply resonant features are more intense than > doubly > Singly

i ii iii iv

532 M S ω4 M 532 S ω4 M S 532 ω4 532 S M ω4

ω4= ω532- ωS + ωM

• Non-linear optical process• Can only be done with very intense (pulsed) lasers• Taking 3 beams and overlapping them to create a new 4th

beam that has its own wavelength (determined by molecule present)

• Detected by monochromator• Which process is responsible for my results?

FOUR WAVE MIXING PROCESS

EXPERIMENTAL SET-UP

3 lasers used for the Four Wave Mixing Process• Mopo (tunable)• Sopo (broadband OPO)

• Can adjust to find fully resonant peaks• 532nm ND: YAG laser

• Wavelength cannot be changed• Selects J value, primarily vibrational changes

532nm Nd: YAG Laser (GCR)

532nm Nd: YAG Laser (GCR)

532nm Nd: YAG Laser

SampleRaman Shifters

SOPO

Monochromator with CCD

MOPO

532 S M ω4

B state, high v’

B state, low v’

X state, high v”

X state, low v”

PROCESS 4 DIAGRAM

DATA ANALYSIS- ORIGINAL RUN

SLOPE OF THE LINE

Slope of lines

• The slope of the line which passes through all of the clusters in that particular area in the pattern was derived

• Slope should be 1 because the axes are ω4 vs. ωM

• Derivation from equation ω4 = ω532- ωS + ωM to y=mx+b

1.ω4 – (ω532 – ωS) = ωM

2.ωM = ω4 + (ωS – ω532)

y = mx + b• Used to help determine spectroscopic constants

VERTICAL SPACING

Intercluster Relationship

• Indicates spacing between the excited levels within the B-state

• Since levels are relatively evenly spaced, levels are not approaching the dissociation limit for the B-state

DIAGONAL SPACING

Intercluster Relationship

• Tells us about the spacing between the excited levels within the higher X-state

• Aren’t converging, so dissociation level hasn’t been reached• All of this information determined is electronic and vibrational

• Next: find rotational information (intracluster relationship)

INTRACLUSTER RELATIONSHIP

FURTHER STUDY• Use simulation (via Excel spreadsheet) to:

• Tune the laser to a specific resonance and decrease the bandwidth to control the number of peaks within a cluster

• Employ same techniques Benjamin Strangfeld described and calculate B’s for designated triangles within a cluster

• Compare coherent 3D spectroscopic constant to literature values

ACKNOWLEDGEMENTS

Peter Chen

Thresa Wells

Benjamin Strangfeld

Aspiring Researchers Program

NSF Grant: NSF CHE-0910232