2D IR Spectroscopy

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Slides for PowerPoint:
Nonlinear and
Two-Dimensional Spectroscopy
Andrei Tokmakoff
MIT Department of Chemistry
Complete Slides
Why 2D IR Spectroscopy?
• IR spectroscopy
– IR probes vibrations intrinsic to all molecules
– Each vibration gives different information
› Structure and dynamics
– Intrinsic time-scale of ~1 ps
• 2D IR spectroscopy: A more sensitive probe
– Characterize vibrational correlations
» Couplings, orientation, exchange
– Resolves congested spectra
& suppresses inhomogeneous broadening
– Quantitative structure-based modeling
Fourier transform 2D IR spectroscopy
Ultrafast nonlinear spectroscopy
mask
Polarization-selective pump-probe experiment
Magic Angle: Vibrational Lifetime
Anisotropy: Reorientation
r  t    S ||  S  
S
||
 2S  
T1
Peak Shift Measurement
ta – tb (fs)
2D IR Interferometer
time/frequency
detection
time/time
detection
2D IR Spectroscopy in pump-probe geometry
Obtaining an Absorptive 2D IR Spectrum
2D IR spectroscopy
• Related to the joint probability P   3 ,final ,  2 ;  1 ,initial 
2 >
= 0c
Frequency Fluctuations
Vibrational Couplings
Chemical Exchange
Chemical exchange and spectral diffusion
• Excite: Initial frequency 1
• Wait for period 2
• Detect: Final frequency 3
2 = 0
2 → 
2D lineshapes: Loss of frequency correlation
Absorptive
S C
Phase
Ellipticity
a
b
Phase slope
Extra Graphics
2D Lineshapes
Rephasing and Non-rephasing
Rephasing and Non-rephasing
2D IR Spectrum of RDC in Hexane
2D IR Spectrum of RDC in Hexane
Polarization-Selective 2D IR Spectroscopy
Projection Angle from Peak Amplitudes

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