The onset of the tetrabonded structure in liquid water

Water properties are dominated by the hydrogen bond interaction that gives rise in the stable liquid phase to the formation of a dynamical network. The latter drives the water thermodynamics and is at the origin of its well known anomalies. The HB structural geometry and its changes remain uncertain and still are challenging research subjects. A key question is the role and effects of the HB tetrahedral structure on the local arrangement of neighboring molecules in water. Here the hydrogen dynamics in bulk water is studied through the combined use of Neutron Compton Scattering and NMR techniques. Results are discussed in the framework of previous studies performed in a wide temperature range, in the liquid, solid, and amorphous states. For the first time this combined studies provide an experimental evidence of the onset of the water tetrahedral network at T~315 K, originally proposed in previous studies of transport coefficients and thermodynamical data; below this temperature the local order in water changes and the lifetime of local hydrogen bond network becomes long enough to gradually develop the characteristic tetrahedral network of water.     

The thermodynamics and structure of liquid water

The additive interatomic interaction model has been used to calculate the thermodynamic functions of liquid water. The O … O and H … H nonbonded interactions were described by Kitaigorodsky potential functions of type 6-exp; for the H … O interactions the hydrogen bond potentials were introduced, and refined using sublimation heats of ice modifications and the normal vibrations of the water dimer. The thermodynamic functions of liquid water were obtained by averaging the corresponding thermodynamic quantities by the Monte Carlo method in the NVT ensemble. Different initial configurations were considered and the results were proved to converge, provided the Markov chain is sufficiently long. The calculated thermodynamic functions were in agreement with the experimental data. An analysis of instantaneous equilibrium configurations was carried out, and conclusions were drawn to what degree the previously proposed structures of liquid water correspond to reality.     

The multipole polarizabilities and hyperpolarizabilities of the water molecule in liquid state: an ab initio study

A charge perturbation variant of the finite-field method has been used to calculate dipole and quadrupole moments, dipole polarizability, hyper- and principal components of high-order polarizabilities of the water molecule in gas and in liquid phase conditions. Calculations were performed for the ground-state water molecule at the MP2 and MP4 levels of theory. The gas phase values determined allow our methodology for extracting polarizabilities to be tested and a properly balanced, moderate-sized basis set to be selected; the results obtained are in very good agreement with experiment and the most accurate previous theoretical estimates. A local field approach is introduced to mimic the electrostatic environment experienced by a water molecule in the liquid. Within this approach, sets of fixed charges are used to generate the desired electric fields and field gradients. Three different liquid phase models and the corresponding sets of electrical properties are examined. The values obtained from these models and for gas-phase are compared. The magnitudes of the dipole and the quadrupole moments increase moving from gas to liquid phase, where the latter shows greater sensitivity to the choice of liquid model. For a liquid phase water molecule the first hyperpolarizability (β) and first higher polarizability (A) increase markedly, actually changing sign, the second hyperpolarizability (γ) also increases but much less dramatically, and components of the second high-order polarizability tensor (B) demonstrate a rearrangement of contributions. The values reported for the hyper- and high-order polarizability tensors are the first such theoretical estimates for liquid water.     

On the structure of a water molecule chemisorbed on a metal surface

A model using the electrostatic image force and the harmonic restoring force has been adapted to find the equilibrium structure of a chemisorbed water molecule on a metal surface. An estimate of the maximum possible increase in the HOH interbond angle upon chemisorption due to image forces is given.     

The analysis of a time-of-flight neutron diffractometer for amorphous materials: the structure of a molecule in a liquid

A comparison is made of the conventional method of using a continuous monochromatic slow neutron beam method of measuring the structure factor of an amorphous material (e.g. a liquid or a glass) and the method using a pulsed beam of heterochromatic neutrons and measurement of their time-of-flight. The Placzek [1] method has been adapted to the analysis of the time-of-flight experiment. The corrections required to convert the measured counting rates to static structure factors are explicitly evaluated for various detector laws and for any incident spectrum. It is shown that there is no particular virtue in equal-path time-of-flight arrangements. There is however a particular interest in a ‘1/v ²’ detector.

The method of analysis is of particular value for the determination of the interference part of the structure factor at high momentum transfer. Some recent experiments on molecular liquids (Clarke and Dore [2 (a] are analysed and it is shown that certain features of the structure of a molecule in the liquid state can be determined. This is a novel result and is of particular importance for liquid water. It is suggested that the D₂O molecule in liquid heavy water at 20°C has a form closer to that in the vapour than that found in ice.     

The structure of the triethylenediamine molecule in an excited electronic state

Ultraviolet absorption spectrum has been observed of triethylenediamine (1,4 diazabicyclo[2.2.2]octane) ($\text{D}{}_{\mathrm{<mtext>3</mtext><mtext>A</mtext><mtext>?</mtext>}}$) vapor in the 2200–2600 Å region, and an analysis has been made of its vibrational structure. The vibronic 0-0 transition was determined to be at 2513.65 Å (39782.8 cm^?1), and in the 2540–2590 Å region there were four hot bands found: two from the a₁′-type vibrational levels and two from the a₂″-type vibrational levels of the ground electronic state. The fine structures of these hot bands were examined with 0.49 Å/mm dispersion (slit width = 50 μm). For each of the two a₂″-type hot bands, a progression with 30 ～ 40 cm^?1 spacings was observed; whereas, no such progressions were found for the a₁′-type hot bands, in which absorption peaks are much more concentrated within narrow ranges. These progressions were attributed to a large-amplitude twisting motion of triethylene-diamine molecule. For explaining the whole energy-level structure, another large-amplitude motion, has been postulated. That is a double-minimum deformation motion along the molecular axis; in each minimum, one of the two NC₃ umbrellas is half-way open and the other NC₃ umbrella is half-way closed. The height of the potential barrier between these two minima has been estimated to be 1586 cm^?1.     

Origin of low-frequency spectrum structure of four-photon scattering in liquid water

-1 has been found experimentally in liquid water. The theoretical interpretation relates these spectral features to an interference of strictional and orientational contributions to the scattered signal. Received: 16 October 1996     

液态水微观结构研究的新进展

液态水有很多奇异特性.近年来,对液态水以何种微观结构形式存在的问题争议激烈.文章介绍了当前对水的微观结构的一些研究及其进展,讨论了液态水中的氢键模式与水的结构关系,进而用一个简化模型探讨了氢键的取向性与强弱性对水的异常行为的作用.     

液态水微观结构研究的新进展

液态水有很多奇异特性.近年来,对液态水以何种微观结构形式存在的问题争议激烈.文章介绍了当前对水的微观结构的一些研究及其进展,讨论了液态水中的氢键模式与水的结构关系,进而用一个简化模型探讨了氢键的取向性与强弱性对水的异常行为的作用.     

The structure of liquid bromine

The atom-atom correlation function for liquid bromine, derived from the X-ray diffraction studies reported in the preceding paper, is compared with the results of Monte Carlo computer simulations and reference site interaction model (RISM) calculations for various bromine-like model molecules. The models used included the two-centre Lennard-Jones interaction model, both by itself and with idealized point quadrupole and quadrupole-induced dipole interaction terms in the computer simulations, and two and three-centre hard-sphere models in RISM. None of these models lead to atom-atom correlation functions which are in good agreement with that obtained from experiment. This suggests that additional information about the interactions between bromine molecules will be needed before the structure of liquid bromine can be completely understood. Finally, by comparing the results of our computer simulations with RISM results for analogous models, we obtain some insight into the accuracy of the reference site interaction model.     

液态金属结构研究新进展

文章介绍了用内耗方法研究金属液态结构的新进展，发现了随温度变化金属液态结构发生不连续的变化，并经差热分析、X射线衍射等实验证实了这种变化．这对认知金属液态结构提供了新的实验依据。     

液态金属结构研究新进展

文章介绍了用内耗方法研究金属液态结构的新进展,发现了随温度变化金属液态结构发生不连续的变化,并经差热分析、X射线衍射等实验证实了这种变化.这对认知金属液态结构提供了新的实验依据.     

The structure of the water dimer

A previously reported self consistent approximation for the pair distribution function is applied to inverse power potentials. Results are reported for the first six virial coefficients over the full range of such potentials. The thermodynamic properties and pair distributions functions are presented for the inverse sixth and twelfth power potentials and are shown to be in close agreement with the results of molecular dynamics and Monte Carlo calculations.     

The electronic structure of the S8 molecule

The UV and X-ray photoelectron spectra of the S₈ molecule are presented together with an SCF-Xα-SW calculation of the electronic structure. The calculated optical transition energies are also presented and compared with the experimental UV absorption spectrum.     

Recent experimental aspects of the structure and dynamics of liquid and supercooled water

Liquid water, the most familiar liquid, is still not completely understood, even less so all the processes in which it participates. The directionality of the bonds and quantum aspects make the establishment of a complete theory difficult, particularly in the case of effective potentials built with spherical electrostatic forces. Recent work has focused on the hydrogen bonds formed between water molecules or with hydrophilic substrates. We describe the present situation of research concerning the so-called anomalies of liquid water at low temperature. Although without direct applications, this problem is consistently an object of discussion, enhanced by results from molecular dynamics simulations. Conversely, because in many situations where water plays a major role, such as, for example, in biology, only a few molecules are involved, the study of confined water is extremely important, sometimes decoupled from the more fundamental studies of bulk water. A short, but far from exclusive, summary of some of the more active domains of research concerning liquid water is given, mainly concerning interactions with other media.