Absorption Spectrum Of Liquid Water Research Articles

TDDFT and the x-ray absorption spectrum of liquid water: Finding the "best" functional.

We investigate the performance of time-dependent density functional theory (TDDFT) for reproducing high-level reference x-ray absorption spectra of liquid water and water clusters. For this, we apply the integrated absolute difference (IAD) metric, previously used for x-ray emission spectra of liquid water [T. Fransson and L. G. M. Pettersson, J. Chem. Theory Comput. 19, 7333-7342 (2023)], in order to investigate which exchange-correlation (xc) functionals yield TDDFT spectra in best agreement to reference, as well as to investigate the suitability of IAD for x-ray absorption spectroscopy spectrum calculations. Considering highly asymmetric and symmetric six-molecule clusters, it is seen that long-range corrected xc-functionals are required to yield good agreement with the reference coupled cluster (CC) and algebraic-diagrammatic construction spectra, with 100% asymptotic Hartree-Fock exchange resulting in the lowest IADs. The xc-functionals with best agreement to reference have been adopted for larger water clusters, yielding results in line with recently published CC theory, but which still show some discrepancies in the relative intensity of the features compared to experiment.

Optical properties of ice and snow.

The interactions of electromagnetic radiation with ice, and with ice-containing media such as snow and clouds, are determined by the refractive index and absorption coefficient (the 'optical constants') of pure ice as functions of wavelength. Bulk reflectance, absorptance and transmittance are further influenced by grain size (for snow), bubbles (for glacier ice and lake ice) and brine inclusions (for sea ice). Radiative transfer models for clouds can also be applied to snow; the important differences in their radiative properties are that clouds are optically thinner and contain smaller ice crystals than snow. Absorption of visible and near-ultraviolet radiation by ice is so weak that absorption of sunlight at these wavelengths in natural snow is dominated by trace amounts of light-absorbing impurities such as dust and soot. In the thermal infrared, ice is moderately absorptive, so snow is nearly a blackbody, with emissivity 98-99%. The absorption spectrum of liquid water resembles that of ice from the ultraviolet to the mid-infrared. At longer wavelengths they diverge, so microwave emission can be used to detect snowmelt on ice sheets, and to discriminate between sea ice and open water, by remote sensing. Snow and ice are transparent to radio waves, so radar can be used to infer ice-sheet thickness. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.

Absorption spectrum of water as a reflection of charge diffusion

The absorption spectrum of liquid water in the range of 103–1013 Hz (from dc conductivity of up to 5 THz IR resonance) is completely and uniformly described by a simple physical model. The model assumes the existence in water of a high concentration of H3O+ and OH− ions (up to 4.5% of the total number of molecules) that exchange protons with H2O molecules on the scale of picoseconds.

Two-photon absorption spectrum of liquid water and the effect of nondiagonal self-energy elements in the self-consistent GW approach on the band gap

Two-photon absorption spectrum of liquid water and the effect of nondiagonal self-energy elements in the self-consistent <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>G</mml:mi><mml:mi>W</mml:mi></mml:mrow></mml:math> approach on the band gap

Possible mechanism of molecular motion in liquid water from dielectric spectroscopy data

The broadband absorption spectrum of liquid water (103–1013Hz) contains a variety of dispersion features spread far apart on the time scale – the dc conductivity, the Debye relaxation, the relaxation-2, and the intermolecular vibration absorption peak at 5.3 THz. In the framework of the common hydrogen-bonding paradigm, the unified description of the features is not available. In an attempt to build a unified picture, we utilize the Frenkel's idea of the oscillation-translation dynamic of particles as a fundamental type of motion inherent to liquids. We develop a model of water structure, in which the dynamics is due to diffusion of particles, neutral H2O molecules and H3O+ and OH– ions - with their periodic localizations and mutual transformations. This model establishes, for the first time, a consistent link between the quoted spectral phenomena. Such currently debatable issues, as anomalous proton mobility and autoionization of water are discussed in the light of the new model. According to the model, water possesses a huge amount of short-living counter ions. This strongly contradicts to many current views on water, but meets support in individual MD simulations.

Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge.

The effects of isotope substitution in liquid water are probed by x-ray absorption spectroscopy at the O K-edge as measured in transmission mode. Confirming earlier x-ray Raman scattering experiments, the D2O spectrum is found to be blue shifted with respect to H2O, and the D2O spectrum to be less broadened. Following the earlier interpretations of UV and x-ray Raman spectra, the shift is related to the difference in ground-state zero-point energies between D2O and H2O, while the difference in broadening is related to the difference in ground-state vibrational zero-point distributions. We demonstrate that the transmission-mode measurements allow for determining the spectral shapes with unprecedented accuracy. Owing in addition to the increased spectral resolution and signal to noise ratio compared to the earlier measurements, the new data enable the stringent determination of blue shift and broadening in the O K-edge x-ray absorption spectrum of liquid water upon isotope substitution. The results are compared to UV absorption data, and it is discussed to which extent they reflect the differences in zero-point energies and vibrational zero-point distributions in the ground-states of the liquids. The influence of the shape of the final-state potential, inclusion of the Franck-Condon structure, and differences between liquid H2O and D2O resulting from different hydrogen-bond environments in the liquids are addressed. The differences between the O K-edge absorption spectra of water from our transmission-mode measurements and from the state-of-the-art x-ray Raman scattering experiments are discussed in addition. The experimentally extracted values of blue shift and broadening are proposed to serve as a test for calculations of ground-state zero-point energies and vibrational zero-point distributions in liquid H2O and D2O. This clearly motivates the need for new calculations of the O K-edge x-ray absorption spectrum of liquid water.

Temperature dependent soft x-ray absorption spectroscopy of liquids.

A novel sample holder is introduced which allows for temperature dependent soft x-ray absorption spectroscopy of liquids in transmission mode. The setup is based on sample cells with x-ray transmissive silicon nitride windows. A cooling circuit allows for temperature regulation of the sample liquid between -10 °C and +50 °C. The setup enables to record soft x-ray absorption spectra of liquids in transmission mode with a temperature resolution of 0.5 K and better. Reliability and reproducibility of the spectra are demonstrated by investigating the characteristic temperature-induced changes in the oxygen K-edge x-ray absorption spectrum of liquid water. These are compared to the corresponding changes in the oxygen K-edge spectra from x-ray Raman scattering.

Ab initio calculation of the electronic absorption spectrum of liquid water.

The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O-H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.

Insights in quantum dynamical effects in the infrared spectroscopy of liquid water from a semiclassical study with an ab initio-based flexible and polarizable force field

The dynamical properties of liquid water play an important role in many processes in nature. In this paper, we focus on the infrared (IR) absorption spectrum of liquid water based on the linearized semiclassical initial value representation (LSC-IVR) with the local Gaussian approximation (LGA) [J. Liu and W. H. Miller, J. Chem. Phys. 131, 074113 (2009)] and an ab initio based, flexible, polarizable Thole-type model (TTM3-F) [G. S. Fanourgakis and S. S. Xantheas, J. Chem. Phys. 128, 074506 (2008)]. Although the LSC-IVR (LGA) gives the exact result for the isolated three-dimensional shifted harmonic stretching model, it yields a blueshifted peak position for the more realistic anharmonic stretching potential. By using the short-time information of the LSC-IVR correlation function; however, it is shown how one can obtain more accurate results for the position of the stretching peak. Due to the physical decay in the condensed phase system, the LSC-IVR (LGA) is a good and practical approximate quantum approach for the IR spectrum of liquid water. The present results offer valuable insight into future attempts to improve the accuracy of the TTM3-F potential or other ab initio-based models in reproducing the IR spectrum of liquid water.

Estimating dry matter content of fresh leaves from the residuals between leaf and water reflectance

At about 1720 nm wavelength, there is an absorption feature of leaf dry matter based on a C−H stretch overtone, which is difficult to detect in fresh green leaves because of the absorption spectrum of liquid water. We applied a method originally proposed in Remote Sensing of Environment by B.-C. Gao and A.F.H. Goetz (Estimating dry matter content of fresh leaves from the residuals between leaf and water reflectance, pp. 137–145, 1994) that used linear regression between the natural logarithm of leaf spectral reflectance and the specific absorption coefficient of liquid water over wavelengths from 1500 to 1800 nm to calculate an expected reflectance spectrum. The residual difference between the measured and expected leaf reflectance spectra enhanced the absorption feature of dry matter. The absorption feature was quantified using the normalized dry matter index (NDMI) based on the contrast between the residual leaf reflectance at 1649 and 1722 nm. NDMI was linearly related to leaf dry matter content (g cm−2) for data obtained in the field (coefficient of determination r 2 = 0.636) and for the leaf optical properties experiment (LOPEX; r 2 = 0.684). Lignin and cellulose contents were also measured during LOPEX, but NDMI was weakly correlated to these variables, indicating NDMI was sensitive to all leaf biochemical constituents. Estimation of dry matter content combined with estimates of water content will facilitate the calculation of the fuel moisture content for prediction of wildfire.

Insights into the ultraviolet spectrum of liquid water from model calculations

With a view toward a better molecular level understanding of the effects of hydrogen bonding on the ultraviolet absorption spectrum of liquid water, benchmark electronic structure calculations using high level wave function based methods and systematically enlarged basis sets are reported for excitation energies and oscillator strengths of valence excited states in the equilibrium water monomer and dimer and in a selection of liquid-like dimer structures. Analysis of the electron density redistribution associated with the two lowest valence excitations of the water dimer shows that these are usually localized on one or the other monomer, although valence hole delocalization can occur for certain relative orientations of the water molecules. The lowest excited state is mostly associated with the hydrogen bond donor and the significantly higher energy second excited state mostly with the acceptor. The magnitude of the lowest excitation energies is strongly dependent on where the valence hole is created, and only to a lesser degree on the perturbation of the excited electron density distribution by the neighboring water molecule. These results suggest that the lowest excitation energies in clusters and liquid water can be associated with broken acceptor hydrogen bonds, which provide energetically favorable locations for the formation of a valence hole. Higher valence excited states of the dimer typically involve delocalization of the valence hole and/or delocalization of the excited electron and/or charge transfer. Two of the higher valence excited states that involve delocalized valence holes always have particularly large oscillator strengths. Due to the pervasive delocalization and charge transfer, it is suggested that most condensed phase water valence excitations intimately involve more than one water molecule and, as a consequence, will not be adequately described by models based on perturbation of free water monomer states. The benchmark calculations are further used to evaluate a series of representative semilocal, global hybrid, and range separated hybrid functionals used in efficient time-dependent density functional methods. It is shown that such an evaluation is only meaningful when comparison is made at or near the complete basis set limit of the wave function based reference method. A functional is found that quantitatively describes the two lowest excitations of water dimer and also provides a semiquantitative description of the higher energy valence excited states. This functional is recommended for use in further studies on the absorption spectrum of large water clusters and of condensed phase water.

Statistical average of model orbital potentials for extended systems: Calculation of the optical absorption spectrum of liquid water

Time-dependent density functional theory (TD-DFT) calculations of the electronic response of molecular and bulk liquid water based on a very accurate orbital-dependent ground-state exchange-correlation potential, the statistical average of (model) orbital potentials (SAOP), and on the adiabatic local density approximation (ALDA) for the exchange-correlation kernel are described. The quality of the calculated excitation energies, both in the molecule and in the liquid, is assessed by comparison to hybrid TD-DFT calculations and experimental data. A combination of classical molecular dynamics simulations and TD-DFT calculations sampling several disordered configurations of a small liquid sample is then used to simulate the optical absorption spectrum in the region of 0–15 eV. The resulting room-temperature absorption profile is discussed in connection with previous TD-DFT calculations as well as with results from Green’s function theory and experiment.

Information Content in O[1s] K-edge X-ray Emission Spectroscopy of Liquid Water

Does the fine-structure in oxygen K-edge X-ray emission (Fuchs et al. Phys. Rev. Lett. 2008, 100, 027801) imply that liquid water is a two-component mixture or is it the signature of a transient OH species arising in the core-excitation process? As with the interpretation of the X-ray absorption spectrum of liquid water, this question is also intensely discussed in the water and X-ray spectroscopy communities. X-ray emission is an independent probe of the electronic structure yielding complementary information on hydrogen bonding in liquid water. In this study, the angular anisotropy in the resonant inelastic soft X-ray scattering (resonant X-ray emission (XE)) spectrum of liquid water is simulated on the basis of ab initio molecular dynamics simulations to allow for direct comparison to recent experimental data (Forsberg et al. Phys. Rev. B 2009, 79, 132203). Theoretical simulations unequivocally show that the difference in angular anisotropy in the water lone-pair features is related to their fundamentally different origin. The high emission-energy peak is primarily due to the contribution from the out-of-plane (1b(1)) lone-pair in intact water molecules. On the other hand, the low emission-energy lone-pair peak originates from the bonding (3a(1)) state and is assigned to a transient OH species formed by ultrafast (<10 fs) photodissociation. The information in the XE spectrum on the structure of liquid water is limited and buried in features arising from excited state dynamics. In combination with available experimental data, the theoretical simulations settle a rising debate on the interpretation of resonant and nonresonant XE spectra of liquid water and there are strong implications for the XE spectroscopy of hydrogen-bonded liquids. The simulations show that the fine-structure in the XE spectrum of liquid water can be explained simply in terms of present day ab initio molecular dynamics simulations.

Dynamic polarizability, Cauchy moments, and the optical absorption spectrum of liquid water: A sequential molecular dynamics/quantum mechanical approach

The dynamic polarizability and optical absorption spectrum of liquid water in the 6-15 eV energy range are investigated by a sequential molecular dynamics (MD)/quantum mechanical approach. The MD simulations are based on a polarizable model for liquid water. Calculation of electronic properties relies on time-dependent density functional and equation-of-motion coupled-cluster theories. Results for the dynamic polarizability, Cauchy moments, S(-2), S(-4), S(-6), and dielectric properties of liquid water are reported. The theoretical predictions for the optical absorption spectrum of liquid water are in good agreement with experimental information.

Comparison of path integral molecular dynamics methods for the infrared absorption spectrum of liquid water

The ring polymer molecular dynamics (RPMD) and partially adiabatic centroid molecular dynamics (PA-CMD) methods are compared and contrasted in an application to the infrared absorption spectrum of a recently parametrized flexible, polarizable, Thole-type potential energy model for liquid water. Both methods predict very similar spectra in the low-frequency librational and intramolecular bending region at wavenumbers below 2500 cm(-1). However, the RPMD spectrum is contaminated in the high-frequency O-H stretching region by contributions from the internal vibrational modes of the ring polymer. This problem is avoided in the PA-CMD method, which adjusts the elements of the Parrinello-Rahman mass matrix so as to shift the frequencies of these vibrational modes beyond the spectral range of interest. PA-CMD does not require any more computational effort than RPMD and it is clearly the better of the two methods for simulating vibrational spectra.

X-ray absorption spectrum of liquid water from molecular dynamics simulations: Asymmetric model

We address the question of the local structure in liquid water by computing the x-ray absorption (XA) spectrum explicitly averaging over configurations from classical and Car-Parrinello molecular dynamics (MD) simulations. We confirm the prediction by Wernet et al. [Science 304, 995 (2004)] that the resulting spectra are not representative for liquid water due to a too large fraction of molecules with two donating hydrogen bonds. The H-bond criterion given by Wernet et al. is, however, not sufficient to predict the XA spectrum for general structures from MD simulations. Only by selecting specific single-donor MD configurations is it possible to represent the liquid water spectrum; this results in an improved and more restrictive geometrical connection between local structure and spectral features in the simulation. The configurations, with one strong and one weak donating hydrogen bond, need to be even more asymmetric than previously assumed. This bonding situation is strongly underrepresented in the simulations.

The relationship between dynamics and structure in the far infrared absorption spectrum of liquid water

Using an intense source of far infrared radiation, the absorption spectrum of liquid water is measured at a temperature ranging from 269 to 323 K. In the infrared spectrum we observe modes that are related to the local structure of liquid water. Here we present a FIR measured spectrum that is sensitive to the low frequency (<100 cm −1) microscopic details that exist in liquid water.

Temperature Dependence of the Visible-Near-Infrared Absorption Spectrum of Liquid Water

Optical absorptivity spectra of ultrapure liquid water over the wavelength range from 550 to 900 nm and over the temperature range from ∼15 to 60 °C are presented. The measured temperature dependen...

Some comments on the paper by Edward S Fry on the visible and near-ultraviolet absorption spectrum of liquid water

It is contended that the most comprehensive collection of data on the visible and near-ultraviolet spectrum of pure liquid water can still be found [Appl. Opt. 38, 1216 (1999)]. The data produced [Appl. Opt. 36, 8710 (1997)] from the integrated light loss in a light-scattering cavity containing water produces a useful set of data, although the error bars presented are underestimated. Furthermore, an oxidative purification step was not incorporated into the water purification procedure to remove residual traces of light-absorbing organic impurities.

Visible and near-ultraviolet absorption spectrum of liquid water: comment

Measurements of the absorption of pure water have been described [Appl. Opt. 38, 1216 (1999)]. This comment on that paper disputes the claims that (1) their list of references on pure water absorption is complete, (2) their result "...provides reliable data in the 320-420-nm region...," and (3) their data agree well with existing data in the literature. The clearest demonstration of these points is made by plotting their data and its associated error bars together with plots of other data in the literature that should be considered significantly more reliable. Finally, for practical applications that require absorption data, a suggestion is made for the best choice of absorption coefficients in the range of 196 nm <or= lambda <or= 700 nm.