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

T 1

Anisotropy: Reorientation

  S ||  S    S ||  2S  

Peak Shift Measurement t a – t b (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 = 0 c 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

Phase Absorptive S



C a b

Ellipticity 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