“fast” camera“slow” camera In both examples, there is still something to “see” This is not the case for most types of spectroscopy

E. T. J. Nibbering et. al, “Vibrational Dynamics of Hydrogen Bonds”, in “Analysis and Control of Ultrafast Photoinduced Reactions”, O. Kuehn and L. Woeste eds., Springer Series in Chemical Physics vol. 87 (2007)

Photon Echo E.L. Hahn (1950) AB CD EF

Three-pulse photon echo E S, k S echo  E S, k S E 1 *, k 1 E 2, k 2  t 1 t3t3 t T= t 2 E 3, k 3 coherence period population period Large homogeneous broadening E 1 *, k 1 E 2, k 2  t3t3 t T E 3, k 3 coherence period population period Large inhomogeneous broadening “free induction decay”

_ _ + + Excitation 1 Detection 3 Excited State Absorption Cross Peaks  Coupling Fundamental Transition (emission) Model absorptive 2D-IR spectrum Elongated peaks indicate correlations between excited and detected frequencies, which denotes the presence of inhomogenous broadening.

N. Huse et. al., “Anharmonic Couplings Underlying the Ultrafast Vibrational Dynamics of Hydrogen Bonds in Liquids”, Phys. Rev. Lett., 95, /1-4 (2005) 2D-IR spectroscopy of acetic acid dimer

T. Brixner et. al., “Two-dimensional spectroscopy of electronic couplings in photosynthesis”, Nature, vol. 434, pp (2005) 2D electronic spectroscopy of the FMO complex

Further reading R. R. Ernst, G. Bodenhausen, A. Wokaun, Principles of Nuclear Magnetic Resonance in One and Two Dimensions; Oxford Press: London, M. Cho, “Coherent Two-Dimensional Optical Spectroscopy”, Chem. Rev. 108, p (2008) J. P. Ogilvie and K. J. Kubarych, “Multidimensional Electronic and Vibrational Spectroscopy: An Ultrafast Probe of Molecular Relaxation and Reaction Dynamics”, in Advances In AMO Physics, E. Arimondo, P. R. Berman and C. C. Lin eds., Elsevier (2009) P. Hamm, “Mukamel for Dummies” (teaching notes, available online, latest version from 2005)