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AN INTRODUCTION TO HIGH RESOLUTION COHERENT MULTIDIMENSIONAL SPECTROSCOPY New 2D and 3D tools for dealing with severe rotational congestion Peter C. Chen, Thresa A. Wells, and Zuri R. House Spelman College, Atlanta GA Benjamin R. Strangfeld Georgia Institute of Technology, Atlanta GA

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Two Dimensional Spectroscopy On-diagonal peaks: Similar to 1D spectroscopy Off-diagonal peaks: Provides new information on the relationship (coupling, correlation, etc.) between peaks. Benefits: improves resolution and can potentially provide new information. I or A or 2D Contour Plot (XYZ surface) Conventional 1D Spectrum (XY plot)

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Nd:YAG Laser Raman Shifter Broadband OPO Monochromator with CCD sample Nd:YAG Laser Tunable OPO or dye laser Simplified Experimental Diagram for 2D Four wave mixing: 3 input beams 1 output beam 1234 1.Tunable dye or OPO 2.Broadband OPO 3.Broadband OPO 4.Output

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Coherent 2D spectrum of NO 2 (off-diagonal region) 2 frequency axes 1 intensity axis

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N=2 N=4 N=6 N=8 Nuclear spin statistics: N= only even values for Ka=0 Doublets due to spin-rotation interaction Additional peaks could be due to: Different Ka subgroups Other vibronic origins Hot bands Extra peaks that disobey selection rules due to conical intersections

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J=1 J=2 J=3 J=4 , cm -1 , cm -1 J=1 J=2 J=3 J=4 cm -1 , cm -1 B=B Boxes are concentric B B Boxes are not concentric Resembles a double Fortrat parabolaX-shaped cluster CLUSTER SHAPE: peaks ordered by J

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Simulated spectra of 79 Br 2, 79,81 Br 2, and 81 Br 2 513 nm 514 nm Simulated 2D: (v 3 = 25 v 4 = 26-50) Simulated 1D spectrum: Peak density is approximately 1000 peaks per nm v 4 =26 v 4 =27v 4 =28v 4 =29 4 (nm) 1 (nm) Intercluster: parabolas ordered by v and isotopomer Intracluster: Peaks ordered by J Peaks compete for limited space along 1D axis: patterns difficult to find

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2D Clusters / information Electronic general location of off-diagonal features Vibrational inter-cluster relationships. Spacing between clusters corresponds to spacing between vibrational levels. Rotational intra-cluster relationships. Shape and size of each cluster depends upon rotational constants.

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81 Br 2 79,81 Br 2 79 Br 2 Result: peaks spatially separated by isotopomer, but congestion remains a problem in many areas. Note the crowding by peaks from from lower lying parabolas, (v 1 >25). Also, no selectivity. 4 (nm) 1 (nm) v 4 =26 v 4 =27 v 4 =28v 4 =29 v 1 =25 P. C. Chen and M. Gomes, JPC A 112, 2999-3001, 2008.

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Multidimensional Multiresonant four wave mixing spectroscopy Singly resonantDoubly resonantTriply resonant Conventional 1D spectroscopy Peak Coherent 2D spectroscopy Continuous LinePeak Coherent 3D spectroscopy PlaneContinuous LinePeak 1 4 4 1 Doubly resonantTriply resonant

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Nd:YAG Laser Nd:YAG Laser Raman Shifter Broadband OPO Monochromator with CCD sample Tunable dye laser Nd:YAG Laser Tunable OPO Simplified Experimental Diagram for 3D Result: two tunable sources: OPO vs. dye laser Approach: scan one, step the other The stepped laser provides the selectivity

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1 2 3 4 5 67 8 910 hgfahgfa hgdahgda gdbagdba gfeagfea hfcahfca hdcahdca 1 3 2 4 3 1 2 4 3 2 1 4 1 2 3 4 1 3 2 4 2 1 3 4 1 2 3 4 3 1 2 4 2 3 1 4 3 2 1 4 1 = dye laser 2 = broadband OPO 3 = tunable OPO 4 = output

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1 2 3 4 hgfahgfa hgdahgda gdbagdba gfeagfea 1 3 2 4 3 1 2 4 3 2 1 4 1 2 3 4 aa fa ha ga aa da ha ga aa da ba ga aa fa ea ga fa ha ga da ha ga da ba ga fa ea ga P (3) = (3) EEE (3) =

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Inter-cluster pattern OPO 44 44 dye laser ea da ha ba fa ha ba ga da ga Process 1Process 2Process 3Process 4 OPO scan: rectangular gridrarerare parallelogram Dye laser scan: rare rectangular grid parallelogramrare fa ha ga da ha ga da ba ga fa ea ga Denominator:

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Process 1Process 2Process 3Process 4 OPO scan Dye laser scan or Intra-cluster pattern In a congested field, triplets (triangles) are easier to identify than doublets or singlets. (For more information on the structure of these triplets, see Ben Strangfelds talk, RD11) Processes 1 and 4 are most likely because of weaker NIR interactions for processes 2 and 3 for most molecules.

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Combined inter-cluster and intra- cluster patterns or Process 1, OPO scan Process 4, OPO scan 44 44 44 44 OPO Type of triangle depends upon whether the DL selects an R-type plane or a P-type plane R-typeP-typeR-typeP-type

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Dye laser Narrowband OPO monochromator R plane P plane 2D Side view of box 3D Dye laser selects OPO scans Mchr scans R selected P selected 2D vs 3D spectra The concentric boxes in 2D space are expanded into 3D space.

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Implications High resolution Coherent 3D spectroscopy can be thought of as a selective version of its 2D counterpart. This selectivity is made by fixing one of the input lasers while scanning the other(s). The 2D spectrum is expanded into 3D space; Fixing one of the narrowband input lasers selects a P- type or R-type plane Scanning the other lasers/mchr produces the resulting slice in this 3D space

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Next 3 talks RD 10 - Thresa A. Wells: NO 2 and intercluster patterns RD 11 - Benjamin R. Strangfeld: Br 2 and intracluster patterns RD 12 - Zuri R. House: I 2 and future directions

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Summary High resolution spectroscopy of large or complex molecules suffers from congestion: Unresolved peaks Lack of identifiable patterns Coherent 2D spectroscopy: Improves resolution Provides peak sorting (by v, J, and isotopomer). Coherent 3D spectroscopy: Further improves resolution over 2D Provides selectivity.

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Current and former group members: Candace Joyner Krystle McBride LaTasha Amisial Kyndra Cottingham Marcia Gomes Rebecca Massey Lindsai Bland Jaimie Miller Kamilah Mitchell Afrah Boigny Thresa Wells - NO 2 Christa Fields Tyler Sugars Notorious Scott Haviland Forrester Zuri House - I 2 Benjamin Strangfeld - Br 2 Collaborators: Paul Houston, Georgia Tech. Funding: NSF grants CHE-0616661 & CHE-0910232