The vibrational spectrum of water in liquid alkanes (original) (raw)
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Water vibrations have strongly mixed intra- and intermolecular character
Nature chemistry, 2013
The ability of liquid water to dissipate energy efficiently through ultrafast vibrational relaxation plays a key role in the stabilization of reactive intermediates and the outcome of aqueous chemical reactions. The vibrational couplings that govern energy relaxation in H2O remain difficult to characterize because of the limitations of current methods to visualize inter- and intramolecular motions simultaneously. Using a new sub-70 fs broadband mid-infrared source, we performed two-dimensional infrared, transient absorption and polarization anisotropy spectroscopy of H2O by exciting the OH stretching transition and characterizing the response from 1,350 cm(-1) to 4,000 cm(-1). These spectra reveal vibrational transitions at all frequencies simultaneous to the excitation, including pronounced cross-peaks to the bend vibration and a continuum of induced absorptions to combination bands that are not present in linear spectra. These observations provide evidence for strong mixing of int...
J Phys Chem a, 2000
The aim of the present paper is to evaluate the influence of the solute-solvent interactions on the infrared spectra of water diluted in liquid CCl 4 and in supercritical xenon, considered as the standard 'inert' solvent. This investigation is based upon FTIR spectra analyzed at the light of both analytical treatments and molecular dynamics simulations. For water in supercritical xenon, the rotational relaxation processes mainly determine the shape of the IR profiles associated with the ν 1 and ν 3 stretching modes. The water molecule rotates almost "freely" due to the isotropic character of the van der Waals interactions applied on the solute. Both the J-model for asymmetric molecular rotor and the molecular dynamics simulations properly account for the band shapes associated with the ν 3 and ν 1 vibrational modes of water. Thus, the rotational dynamics of water is primarily governed by "collisional" interactions with the neighboring solvent molecules. For water dissolved in liquid CCl 4 , a structural analysis based upon the simulated radial distribution functions provides evidence for the existence of a short-ranged C‚‚‚H-O arrangement between the solute and its neighboring solvent molecules. It is also found that the reorientational dynamics of water are more perturbed than those in SC xenon fluid, due to the weakly anisotropic character of the water-CCl 4 interactions. In particular, the reorientational motions of the z symmetry axis of water appear to be more specifically affected. We emphasize that a correct treatment of the rotational dynamics of water in liquid CCl 4 is provided only by simulation methods that, in contrast to the analytical J model, include the details of the intermolecular solute-solvent potential. Although the transition dipole moment of the ν 3 mode of water is only weakly affected by the interactions, the oscillator strength of the ν 1 internal mode is found to be enhanced compared to its gas-phase value, a result related to the increase of the transition dipole moment due to the water-solvent interactions. Finally, we argue that the spectral properties can be interpreted without invoking a specific H-bond contribution in the intermolecular potential.
A molecular dynamics study of the OH stretching vibrational spectrum of liquid water
Chemical Physics Letters, 1986
A classical molecular dynamics (CMD) study has been carried out to investigate the OH stretching spectrum of liquid water. The potential used is the simple point charge model modified to include anharmonic vibrational potentials. A series of CMD runs were made for a system of 100 water molecules. Spectral functions for infrared, Raman and inelastic neutron scattering were directly computed from the trajectories of the CMD. The computed spectral band shapes are in good qualitative agreement with experimentally measured spectra.
An improved potential for non-rigid water molecules in the liquid phase
Chemical Physics Letters, 1983
A modification of the central-force model for liquid water is proposed; a spectroscopic potential is adapted to describe the intramolecular interactions. Gas-liquid shifts of internal vibrational frequencies obtained from MD simulations are in good agreement with available spectroscopic data.
Vibrational Spectroscopy and Dynamics of Water
We present an overview of recent static and time-resolved vibrational spectroscopic studies of liquid water from ambient conditions to the supercooled state, as well as of crystalline and amorphous ice forms. The structure and dynamics of the complex hydrogen-bond network formed by water molecules in the bulk and interphases are discussed, as well as the dissipation mechanism of vibrational energy throughout this network. A broad range of water investigations are addressed, from conventional infrared and Raman spectroscopy to femtosecond pump−probe, photon-echo, optical Kerr effect, sum-frequency generation, and two-dimensional infrared spectroscopic studies. Additionally, we discuss novel approaches, such as two-dimensional sum-frequency generation, three-dimensional infrared, and two-dimensional Raman terahertz spectroscopy. By comparison of the complementary aspects probed by various linear and nonlinear spectroscopic techniques, a coherent picture of water dynamics and energetics emerges. Furthermore, we outline future perspectives of vibrational spectroscopy for water researches. CONTENTS
Structure and dynamics of water remain a challenge. Resolving the properties of hydrogen bonding lies at the heart of this puzzle. We employ ab initio Molecular Dynamics (AIMD) simulations over a wide temperature range. The total simulation time was < 2 ns. Both bulk water and water in the presence of a small hydrophobic molecule were simulated. We show that large-angle jumps and bond bifurcations are fundamental properties of water dynamics and that they are intimately coupled to both local density and hydrogen bond strength oscillations in scales from about 60 to a few hundred femtoseconds: Local density differences are the driving force for bond bifurcations and the consequent large-angle jumps. The jumps are intimately connected to the recently predicted hydrogen bond energy asymmetry. Our analysis also appears to confirm the existence of the so-called negativity track provided by the lone pairs of electrons on the oxygen atom to enable water rotation. S tatic and dynamic properties of both bulk and solvation water have garnered a lot of attention including several conflicting hypotheses. For example, the picture that water rotation can be desribed by simple Debye rotational diffusion was shown to be too simplistic by Laage and Hynes who demonstrated, using computer simulations, that instead of smooth rotation, water molecules undergo large-angle jumps 1 . This has since been confirmed by experiments 2 and independent simulations 3 . In a recent contribution, ab initio simulations of Kühne and Khaliullin 4 resolved the controversy regarding the interpretation of a series of x-ray experiments 5,6 that suggested water having anisotropic structure. Their simulations showed that the structure of water is tetrahedral but the energetics of the hydrogen bonds (HBs) are asymmetric.
We report an analysis of the stretching peak appearing in the IR experimental spectra of liquid water. In the literature, ATR-IR spectroscopic measurements were repeatedly performed in a wide range of temperature and gave rise to a lively debate among scientists. In particular a two components model related to H-bond complexes of different strength have been proposed in order to justify the existence of two types of molecules as it appears from the spectroscopic data. At the opposite, Molecular Dynamics simulations support a multistate (continuum) system of H bond having different strength giving rise to a (locally) tetrahedral description of liquid water. We will show that liquid water is a quantum two-level system according to the predictions of Quantum Electrodynamics (QED) and that several features (the asymmetric band profile, the existence of an isosbestic point and the modifications of the vibrational stretching band with the temperature) cannot be fully justified in the real...
Dynamics of water molecules in an alkaline environment
The Journal of Chemical Physics, 2002
We report on a two-color mid-infrared pump-probe spectroscopic study of the dynamics of the OH stretch vibrations of HDO molecules dissolved in a concentrated ͑10 M͒ solution of NaOD in D 2 O. We observe that spectral holes can be created in the broad OH stretch absorption band that change neither position nor width on a picosecond time scale. This behavior differs strongly from that of pure HDO:D 2 O where rapid spectral diffusion ( c Ϸ600 fs) occurs. The long-living inhomogeneity indicates that a concentrated aqueous NaOX (XϭH,D) solution has a very static hydrogen-bond network. The results also show that the absorption band of the OH stretch vibration consists of two separate classes of OH groups with very different vibrational lifetimes. For component I, the lifetime of the OH stretch vibration is ϳ600 fs and increases with OH frequency, which can be explained from the accompanying decrease in the strength of the hydrogen-bond interaction. This component represents HDO molecules of which the OH group is bonded to a D 2 O molecule via a DO-H¯OD 2 hydrogen bond. For component II, the lifetime is ϳ160 fs, and does not show a significant frequency dependence. This component represents HDO molecules that are hydrogen bonded to a D 2 O molecule or an OD Ϫ ion. The short, frequency-independent vibrational lifetime of component II can be explained from the participation of the HDO molecule and its hydrogen-bonded partner in deuteron and/or proton-transfer processes.
The Journal of Chemical Physics, 1996
The structure, dynamical, and electronic properties of liquid water utilizing different hybrid density functionals were tested within the plane wave framework of first-principles molecular dynamics simulations. The computational approach, which employs modified functionals with short-ranged Hartree-Fock exchange, was first tested in calculations of the structural and bonding properties of the water dimer and cyclic water trimer. Liquid water simulations were performed at the state point of 350 K at the experimental density. Simulations included three different hybrid functionals, a meta-functional, four gradient-corrected functionals, and the local density and Hartree-Fock approximations. It is found that hybrid functionals are superior in reproducing the experimental structure and dynamical properties as measured by the radial distribution function and self-diffusion constant when compared to the pure density functionals. The local density and Hartree-Fock approximations show strongly over-and understructured liquids, respectively. Hydrogen bond analysis shows that the hybrid functionals give slightly smaller average numbers of hydrogen bonds than pure density functionals but similar hydrogen bond populations. The average molecular dipole moments in the liquid from the three hybrid functionals are lower than those of the corresponding pure density functionals. † Part of the special issue "Michael L. Klein Festschrift".