Slides for PowerPoint:
Nonlinear and Two-Dimensional Spectroscopy
Andrei TokmakoffMIT 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
1T
|| ||r t S S S 2S
Peak Shift Measurement
ta – tb (fs)
2D IR Interferometer
time/frequencydetection
time/timedetection
2D IR Spectroscopy in pump-probe geometry
Obtaining an Absorptive 2D IR Spectrum
2D IR spectroscopy
Frequency Fluctuations Vibrational Couplings Chemical Exchange
• Related to the joint probability
3,final 2 1,initialP , ;
2 = 0 2 > c
• Excite: Initial frequency 1
• Wait for period 2
• Detect: Final frequency 3
Chemical exchange and spectral diffusion
2 = 0
2 →
AbsorptiveCS
2D lineshapes: Loss of frequency correlation
Phase
a
b
Phase slope
Ellipticity
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