Multi-dimensinal spectroscopies of liquid
Two-dimensional infrared spectroscopy
Ultrafast Dynamics of Liquid Water: Energy Relaxation and Transfer Processes of the OH Stretch and the HOH Bend
The vibrational energy relaxation and transfer processes of the OH stretching and
the HOH bending vibrations in liquid water are investigated via the theoretical
calculation of the pump-probe spectra obtained from non-equilibrium molecular dynamics
simulations with the TTM3-F interaction potential.
The excitation of the OH stretch induces an instantaneous response of the high
frequency librational motions in the 600-1000 cm-1 range.
In addition, the excess energy of the OH stretch of a water molecule quickly
transfers to the OH stretches of molecules in its first hydration shell with
a time constant of ~50 fs, followed by relaxation to the HOH bends of the surrounding
molecules with a time constant of 230 fs.
The excitation of the HOH bend also results in the ultrafast excitation of the high
frequency librational motions.
The energy of the excited HOH bend of a water molecule decays, with a time constant
of 200 fs, mainly to the relaxation of the HOH bends of its surrounding molecules.
The energies of the HOH bends were found to transfer quickly to the intermolecular
motions via the coupling with the high frequency librational motions.
The excess energy of the OH stretch or the HOH bend relaxes to the high frequency
intermolecular librational motions and eventually to the hot ground state with
a time scale of ~1 ps via the coupling with the librational and translational motions.
The energy relaxation and transfer processes were found to depend on the local hydrogen
bonding network; the relaxations of the excess energy of the OH stretch and the HOH
bend of four- and five-coordinated molecules are faster than those of
a three-coordinated molecule due to the delocalization of the vibrational motions
of the former (four- and five-coordinated molecules) compared to those of
the later (three-coordinated molecules).
The present results highlight the importance of the high frequency intermolecular
librational modes in facilitating the ultrafast energy relaxation process
in liquid water via their strong nonlinear couplings with the intramolecular
OH stretching and HOH bending vibrations.
Ultrafast dynamics of liquid water: Frequency fluctuations of the OH stretch and the HOH bend
Frequency fluctuations of the OH stretch and the HOH bend in liquid water are
reported from the third-order response function evaluated using the TTM3-F
potential for water. The simulated two-dimensional infrared (IR) spectra of
the OH stretch are similar to previously reported theoretical results.
The present study suggests that the frequency fluctuation of the HOH bend
is faster than that of the OH stretch. The ultrafast loss of the frequency
correlation of the HOH bend is due to the strong couplings with the OH stretch
as well as the intermolecular hydrogen bond bend.
Ultrafast energy relaxation and anisotropy decay of the librational motion
in liquid water: A molecular dynamics study
We theoretically investigate intermolecular motions in liquid water
in terms of third-order infrared (IR) spectroscopy. We calculate
two-dimensional (2D) IR spectra, pump-probe signals, and three-pulse
stimulated photon echo signals from the combination of equilibrium and
nonequilibrium molecular dynamics simulations. The 2D IR spectra and
the three-pulse photon echo peak shift exhibit that the frequency
correlation of the librational motion decays with a time scale of 100 fs.
The two-color 2D IR spectra and the pump-probe signals reveal that
the energy transfer from the librational motion at 700 cm-1 to
the low frequency motion below 300 cm-1 occurs with a time scale of 60 fs
and the subsequent relaxation to the hot ground state takes place on
a 500 fs time. The time scale of the anisotropy decay of the librational
motion is found to be ~115 fs. The energy dissipation processes are
investigated in detail by using the nonequilibrium molecular dynamics
simulation, in which an electric field pulse is applied. We show that
the fast energy transfer from the librational motion to the low frequency
motion is mainly due to the librational-librational energy transfer.
We also show that the fast anisotropy decay mainly arises
from the rapid intermolecular energy transfer.
Yagasaki, Ono & Saito, J.Chem.Phys.131, 164511 (2009).
Molecular Dynamics Simulation of Nonlinear Spectroscopies of
Intermolecular of Motions in Liquid Water
Water is the most extensively studied of liquids because of both its ubiquity
and its anomalous thermodynamic and dynamic properties.
The properties of water are dominated by hydrogen bonds and hydrogen bond network
Fundamental information on the dynamics of liquid water has been provided
by linear infrared (IR), Raman, and neutron-scattering experiments;
molecular dynamics simulations have also provided insights.
Recently developed higher-order nonlinear spectroscopies open new windows
into the study of the hydrogen bond dynamics of liquid water.
For example, the vibrational lifetimes of stretches and a bend, intramolecular
features of water dynamics, can be accurately measured and are found to be on
the femtosecond time scale at room temperature.
Higher-order nonlinear spectroscopy is expressed by a multitime correlation
function, whereas traditional linear spectroscopy is given by a one-time correlation function.
Thus, nonlinear spectroscopy yields more detailed information on the dynamics
of condensed media than linear spectroscopy. . . .
Yagasaki & Saito, Acc.Chem.Res.42, 1250 (2009).
Ultrafast intermolecular dynamics of liquid water: A theoretical study on
two-dimensional infrared spectroscopy
Physical and chemical properties of liquid water are dominated
by hydrogen bond structure and dynamics. Recent studies of nonlinear
vibrational spectroscopy of intramolecular motion provided new insight
into ultrafast hydrogen bond dynamics. However, our understanding of
intermolecular dynamics of water is still limited. We theoretically
investigate intermolecular dynamics of liquid water in terms of
two-dimensional infrared (2D IR) spectroscopy. The 2D IR spectrum of
intermolecular frequency region (< 1000 cm-1) is calculated by using
the equilibrium and non-equilibrium hybrid molecular dynamics method.
We find the ultrafast loss of the correlation of the libration motion
with the time scale of approximately 110 fs. It is also found that
the energy relaxation from the libration motion to the low frequency
motion takes place with the time scale of about 180 fs. We analyze
the effect of the hindered translation motion on these ultrafast dynamics.
It is shown that both the frequency modulation of libration motion and
the energy relaxation from the libration to the low frequency motion
significantly slow down in the absence of the hindered translation motion.
The present result reveals that the anharmonic coupling between the hindered
translation and libration motions is essential for the ultrafast relaxation
dynamics in liquid water
Waiting time dependence of 2D IR cpectra of lqiuid water
Yagasaki & Saito, J.Chem.Phys.128, 154521 (2008).
Two-dimensional Raman spectroscopy
Fifth-order two-dimensional Raman spectroscopy of liquid water, crystalline
Ice Ih and amorphous ices: Sensitivity to anharmonic dynamics and local
hydrogen bond network structure
Theoretical study of off-resonant fifth-order two-dimensional (2D)-Raman
spectroscopy is made to analyze the intermolecular dynamics of liquid and
solid water. The 2D-Raman spectroscopy is susceptible to the nonlinear
anharmonic dynamics and local hydrogen bond structure in water. It is found
that the distinct 2D-Raman response appears as the negative signal near
the t2 axis.
The origin of this negative signal for t2 < 15 fs is from the nonlinear
polarizability in the librational motions, whereas that for
30 fs < t2 < 150 fs
is attributed to the anharmonic translational motions. It is found that
the mechanical anharmonicity and nonlinear polarizability couplings among
modes clearly can be observed as the sum- and difference-frequency peaks
in the 2D-Raman spectrum (i.e., Fourier transforms of the response). The
2D-Raman spectroscopies of ice Ih and amorphous ices, i.e., low-density,
high-density, and very high-density amorphous ices, are also investigated.
It is found that the 2D-Raman spectroscopy is very sensitive to the anisotropy
of the structure of ice Ih. The strong HB stretching band is seen in the
2D-Raman spectroscopy of the polarization directions parallel to the c-axis,
whereas the contributions of the librational motion can be also seen in the
spectrum with the polarization directions parallel to the a-axis. The 2D-Raman
spectroscopy is also found to be also very sensitive to the differences in
local hydrogen bond network structures in various amorphous phases.
2D Raman signal of lqiuid water
2D Raman spectrum of lqiuid water
Saito & Ohmine, J.Chem.Phys.125,084506 (2006).