Wave Packet Study of Ultrafast Relaxation in Ice Ih and Liquid Water. Resonant Intermolecular Vibrational Energy Transfer

Abstract

By using quantum chemistry, the fundamental normal modes and the frequencies of ice Ih and room-temperature water clusters containing up to 15 water molecules are constructed. These normal modes are then used on the basis of assumed harmonic dynamics for analyzing the survival probability and energy decay of wave packets which reflect symmetric and asymmetric stretch excitations in single water molecules. Following symmetric stretch excitation, it is found that the wave packet survival probability and the OH stretch mode energy both decay on a sub-100-fs time scale in both phases. For asymmetric stretch excited states, the characteristic relaxation time is below 100 fs in ice Ih, but it is slower in liquid water. In both cases, it is found that the dynamics are truly many-body in character, since clusters of size ∼15 are required to converge the early time behavior of the OH mode relaxation processes. The results support the suggestion of Woutersen and Bakker (Nature 1999, 402, 507-509) that, in liquid water, intermolecular vibrational energy transfer occurs on a sub-100-fs time scale. The dynamics appear to be predominantly of harmonic character.

Libration induced stretching mode excitation for pump-probe spectroscopy in pure liquid water

“…Such VET has already been observed by Woutersen and Bakker. 23 Poulsen et al 24 simulated VET in pure water, and found a time transfer from 80 to 250 fs, in very good agreement with our data. This allows us to depict the model of diffusion in pure water as follows: the pump pulse, via libration modes, excites OH vibrator at a given frequency.…”

Probing intermolecular couplings in liquid water with two-dimensional infrared photon echo spectroscopy

“…5 Alter-natively, intermolecular ET was studied by using harmonic approximations. 8,9 In this work, we use numerical integration of the Schrödinger equation 10 ͑NISE͒ in a fully anharmonic nonadiabatic simulation procedure, explicitly treating the intermolecular coupling, as well as fluctuations and anharmonicities of transition frequencies and dipole moments, to calculate the 2DIR-PE and pump probe ͑PP͒ response of OH stretch vibrations in liquid water. With this new procedure, we find excellent agreement with the recent experimental results.…”

Vibrational dynamics of hydrogen bonds

“…As a result the fastest dynamics of water (500 nm thickness) at room temperature has now been determined with 70 fs time resolution. These recent experimental results on neat water emphasize the necessity of theoretical studies on the determination of the couplings of librational modes with the O−H stretching oscillator [194], as well as intermolecular resonant vibrational energy transfer [195,196], fluctuations of the hydrogen bond network of neat water [176,197], and reorientational dynamics [198]. 7.9).…”