Multi-Dimensional IR Spectroscopy of Acetic Acid Dimers and Liquid Water N. Huse 1, J. Dreyer 1, E.T.J.Nibbering 1, T. Elsaesser 1 B.D. Bruner 2, M.L. Cowan 2, J.R. Dwyer 2, B. Chugh 2, R.J.D. Miller 2 1 Max-Born-Institute for Nonlinear Optics und Short Pulse Spectroscopy Berlin, Germany 2 Department of Chemistry and Physics University of Toronto, Canada Partially funded by SFB 450
Outline Multi-dimensional spectroscopy Couplings in acetic acid dimers Structural dynamics in pure water
From Linear to Multi-Dimensional Spectroscopy Linear spectroscopy 2D spectroscopy T Which transitions couple to each other? What is the broadening mechanism? How fast are the dynamics? Excitation ν 1 Detection ν 3 Signals of anharmonic oscillators Fundamental transition Excited state absorption Cross peaks coupling Excitation ν 1 + + T Detection ν 3
Heterodyne Detected Photon Echoes T τ 3 τ 1 klo, -k1 + k2 + k3 Infrared detector array ν = 8cm -1 k LO Monochromator Spectrograms for different delays of τ T 1 LO τ 3 τ τ 1 1 1 2 3 = τ 3-1 ν 3 ν 3 ν3 Field extraction Fourier Pulse delay transform S(τ 1,ν 3 ) E(τ 1,ν 3 ) E(ν 1,ν 3 )
Acetic Acid Dimers Cyclic acetic acid dimer OH-stretching vibration well-defined geometry Absorbance (OD) 0.3 0.2 0.1 Phenol in C 2 Cl 4 Acetic Acid in CCl 4 2 levels vs. multi-level structure 0.0 3500 3000 2500 Wavenumber (cm -1 v OH =1 v=1,i red-shift of ν(o-h) v OH =0 v=0,i O H O H O very strong broadening structured bandshape
Acetic Acid Dimers Cyclic acetic acid dimer OH-stretching vibration ip bending 148 cm -1 ip stretching -143 cm -1 Absorbance (OD) 0.3 0.2 0.1 Phenol in C 2 Cl 4 Acetic Acid in CCl 4 2 levels vs. multi-level structure 0.0 3500 3000 2500 Wavenumber (cm -1 v OH =1 v OH =0 v=1,i v=0,i O H O H O Broadening mechanism: anharmonic coupling to low-frequency modes Fermi resonances? Heyne et al., J. Chem. Phys. 121 (2004), 902
Fermi Resonances 3200 1. 1 Fermi resonances 3000 0. 0 ν OH 1 δ OH 2 (ν OH /2δ OH ) g (ν OH /2δ OH ) u Excitation Frequency ν 1 2800 2600 3200 3000 2800 2600 T=0fs T=400fs 2600 2800 3000 3200 Detection Frequency ν 3-1 Signal Amplitude (norm.) 1 δ OH =1 0 0 ν OH,δ OH =0 Transitions: ν OH, δ OH, ν CO, ν C=O 1.0 0.5 0.0 T=0fs T=400fs Profiles 2600 2800 3000 3200 Detection Frequency ν 3 0.2 0.0 Absorbance (OD)
1.0 0 0 0.0 2 439.0 0 0 Ab-initio Calculations Theory Experiment IR Intensity (arb.u.) 0.50 0.25 Linear Nonlinear Linear Nonlinear 1 Excitation Frequency ν 1 3200 3000 2800 2600 T=400 fs -1 2600 2800 3000 3200 T=400 fs 2600 2800 3000 3200 0-1 Detection Frequency ν 3 Detection Frequency ν 3 Ab-initio calculations: Fermi resonances dominate 2D spectra Cubic coupling constants with i = ν bu OH j (a g ) δoh νc O δoh k (b u ) νc O δoh δoh -141-125 98 Dreyer, Int. J. Quantum Chem. (in press) νc=o νc O -85
Liquid Water Hydrogen bonds determine the structure and other properties of water MD simulation of water (from Parinello group) Inverse Absorption Length 10000 1000 Linear absorption spectrum Wieliczka '89 100 4000 3000 2000 1000 Frequency Wielczka et al., Appl. Opt. 28 Fluctuating geometry HOD in D 2 O: Stenger et al., Phys. Rev. Lett. 027401 (2001) Stenger et al., J. Phys. Chem A 105 (2001), 2929 OH stretching OH bending Librations
Ultrafast Timescales in Liquid Water O-H stretching vibration Librations O-H stretching modes (3400 cm -1 ) O-H bending mode (1650 cm -1 ) Fast librations ( 1500 cm -1 ) Vibrational lifetimes ~ 0.01 ps ~ 0.02 ps ~ 0.03 to 0.1 ps ~ 0.2 ps Microscopic dynamics of hydrogen bonds is ultrafast.
Frequency-Resolved Transient Grating T 1 3 LO 2 τ 1 =0fs Spectral diffusion signal decay at the edges within 50 fs Energy transfer anisotropy decay in less than 100 fs Pulse delay 50fs Population relaxation OH stretch lifetime = 190 fs
Correlation Spectra of Pure Water 3500 T=0fs T=50fs Pulse sequence 1.0001 ν 1 3250 τ 1 T=0 fs T=50 fs 0.04762 0 3000 2750 3000 3250 3500 ν 3 1 2 3 LO 2750 3000 3250 3500 ν 3 3-1.000 Microscopic origin: librational modes with ω > ω(o...o) Inverse Absorption Length 3000 1000 300 Wielczka et al., Appl. Opt. 28 OH bending Librations 1500 1000 500 Frequency
Conclusions Heterodyne photon echo spectroscopy delivers full information on couplings and line broadening mechanism Fermi resonances dominate 2D spectra of acetic acid although cubic coupling constants are similar for coupling to low-frequency modes (Huse et al., submitted) Loss of inhomogeneity in liquid water within 50 fs due to librational modes of the hydrogen bond network, T 1 200 fs (Cowan et al., Nature 434 (2005), 199)