Two-dimensional infrared spectroscopy and ultrafast anisotropy decay of water

Abstract

We introduce a sparse-matrix algorithm that allows for the simulation of two-dimensional infrared (2DIR) spectra in systems with many coupled chromophores. We apply the method to bulk water, and our results are based on the recently developed ab initio maps for the vibrational Hamiltonian. Qualitative agreement between theory and experiment is found for the 2DIR spectra without the use of any fitting or scaling parameters in the Hamiltonian. The calculated spectra for bulk water are not so different from those for HOD in D(2)O, which we can understand by considering the spectral diffusion time-correlation functions in both cases. We also calculate the ultrafast anisotropy decay, which is dominated by population transfer, finding very good agreement with experiment. Finally, we determine the vibrational excitation diffusion rate, which is more than two orders of magnitude faster than the diffusion of the water molecules themselves.

Hydration Dynamics of Aqueous Nitrate

“…Despite the clear distinction between excitation and probing of lower and higher frequency modes in our experiments, we observe in-plane randomization of the transition dipole moment orientations on an ultrafast timescale. Excitation transfer alone, as for example between different water molecules with overlapping OH stretch spectra 51 , is not sufficient to account for this observation. For illustration consider the schematic picture of solvated nitrate ions in Fig.12.…”

OH and NH Stretching Vibrational Relaxation of Liquid Ethanolamine

“…Its vibrational relaxation dynamics following an initial OH-stretching excitation has been studied extensively by femtosecond (fs) time-resolved mid-infrared (MIR) spectroscopy. Immediately after laser-excitation of the v = 0 to v = 1 transition of the OH-stretching mode, the excess energy rapidly delocalizes onto neighboring water molecules thereby giving rise to an ultrafast loss of memory regarding the frequency of excitation as well as the orientation of the associated transition dipole [8][9][10]. These dynamics are facilitated by strong OH transition dipole interactions, i.e.…”

Dynamics of Resonant Energy Transfer in OH Vibrations of Liquid Water

“…If we assume that the Nparticle probability density W N is approximated as a product of N spherical symmetric two-particle probability density functions: (18) where g(r) is the pair correlation function of intermolecular OH dipoles, we can simplify the part of intermolecular pathway of Eq. (15) in the thermodynamic limit where N,V → and N/V = ρ, 22,23,25 and we get the survival probability within the IPA as (19) where .…”

“…(15), (19), and (20)] and the validities of them are assessed by comparing their predictions of survival probability with that of "exact" ME, Eq. (7), calculated by solving the master equation, Eq.…”

“…Due to the couplings, when an OH bond is excited, the excited energy is transferred to nearby OH bonds which are resonant with the excited OH bond. The energy transfer process is manifested in spectroscopic data such as IR and Raman line shapes, 7,[12][13][14][15][16] vibrational pump-probe anisotropy, 14,[17][18][19] and two-dimensional surface vibrational spectroscopy. 20 The manifestation of energy transfer hinders one extracting the information about local spectral dynamics directly from the analysis of experimental results.…”