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

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 , ;

t2 = 0

t2 > tc

• Excite: Initial frequency w1

• Wait for period t2

• Detect: Final frequency w3

Chemical exchange and spectral diffusion

t2 = 0

t2 →

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