Asymmetric OH Research Articles

SFG study on potential-dependent structure of water at Pt electrode/electrolyte solution interface

Structure of water at Pt/electrolyte solution interface was investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at ca. 3200 cm −1 and ca. 3400 cm −1, which are known to be due to the symmetric OH stretching ( υ 1) of tetrahedrally coordinated, i.e., strongly hydrogen bonded “ice-like” water, and the asymmetric OH stretching ( υ 3) of water molecules in a more random arrangement, i.e., weakly hydrogen bonded “liquid-like” water, respectively. The SFG intensity strongly depended on electrode potential. Several possibilities are suggested for the potential dependence of the SFG intensity.

Interfacial water structure at polymer gel/quartz interfaces investigated by sum frequency generation spectroscopy

Interfacial structures of water at polyvinyl alcohol (PVA) and poly(2-acrylamido-2-methypropane) sulfonic acid sodium salt (PNaAMPS)/quartz interfaces were investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at 3200 and 3400 cm(-1), corresponding to the symmetric OH stretching of tetrahedrally coordinated, i.e., strongly hydrogen bonded "ice-like" water, and the asymmetric OH stretching of water in a more random arrangement, i.e., weakly hydrogen bonded "liquid-like" water, respectively, in both cases. The "liquid-like" water became dominant when the PVA gel was pressed against the quartz surface. The relative intensity of the SFG signal due to the "liquid-like" water to that due to the "ice-like water" at the quartz surface modified with a self-assembled monolayer of aminopropyltrimethoxysilane (APS) became higher when the negatively charged PNaMPS gel was contacted to the APS modified quartz surface in a solution of pH = 12, where the surface was negatively charged and electrostatic repulsive interaction and low friction were present between the PNaMPS gel and the APS modified surface. It, however, did not change in a solution of pH = 2, where the surface was positively charged and electrostatic attractive interaction and very high friction were present between the PNaMPS gel and the APS modified surface. These results suggest the important role of water structure for small friction at the polymer gel/solid interface.

An automated FTIR method for the routine quantitative determination of moisture in lubricants: An alternative to Karl Fischer titration

An accurate primary Fourier transform infrared (FTIR) method for the determination of moisture in mineral and ester based lubricants has been developed based on the extraction of moisture into dry acetonitrile. FTIR evaluation of acetonitrile extracts from new and used lubricants as well as common lubricant additives and contaminants which might co-extract indicated that phenolic constituents interfered significantly with moisture measurements. By measuring moisture at 3676 cm −1 on the shoulder of the asymmetric OH stretching band, spectral interferences from extracted phenolic constituents were minimized. The spectra of calibration standards (0–2100 ppm), prepared by gravimetric addition of water to dry acetonitrile, were recorded in a 1000-μm CaF 2 transmission flow cell and produced linear standard curves having an S.D. of ∼±20 ppm. Lubricant sample preparation involved the vigorous shaking (20 min) of a 1:1.5 (w/v) mixture of lubricant and dry acetonitrile, centrifugation to separate the phases, acquisition of the FTIR spectrum of the upper acetonitrile layer, and subtraction of the spectrum of the dry acetonitrile used for extraction. A Continuous Oil Analyzer and Treatment (COAT ®) FTIR system was programmed to allow the automated analysis of acetonitrile extracts, and the methodology was validated by analyzing 58 new and used oils, independently analyzed by the Karl Fischer (KF) method. Linear regression of FTIR versus KF results for these oils produced a linear plot with a between-method S.D. of ±80 ppm. As implemented on the COAT ® system, this FTIR method is capable of analyzing 72 acetonitrile extracts/h and provides a high-speed alternative to the KF titrimetric procedures for the determination of water in lubricants.

Nature of water in nacre: A 2D Fourier transform infrared spectroscopic study

In this work, the interactions of aragonite and organic matrix in nacre with water are investigated using two-dimensional (2D) Fourier transform infrared (FTIR) spectroscopy. The 2D-FTIR analysis revealed four bands in the OH stretching region at around 3550, 3445, 3272 and 3074 cm −1. Two additional bands were found at around 3616 and 3282 cm −1 after deconvolution of the nacre spectrum. The bands at around 3616 and 3550 cm −1 are assigned to asymmetric and symmetric OH stretching of partially hydrogen bonded water molecules. The bands at around 3445 and 3272 cm −1 are assigned to asymmetric and symmetric OH stretching of water molecules fully hydrogen bonded with surrounding water molecules. Presence of above bands in the nacre spectrum suggests that water, in form of clusters, is present in protein matrix and aragonite pores. Water may also hydrogen bond with the organic matrix. The bands observed at 3282 and 3074 cm −1 are assigned to asymmetric and symmetric OH stretching of water molecules, chemisorbed on surfaces of aragonite platelets. Polarization experiments suggest that H–O–H plane of water molecules is along to c-axis of aragonite platelets.

Theoretical study of the changes in the vibrational characteristics arising from the hydrogen bonding between Vitamin C ( l-ascorbic acid) and H 2O

The vibrational characteristics (vibrational frequencies, infrared intensities and Raman activities) for the hydrogen-bonded system of Vitamin C ( l-ascorbic acid) with five water molecules have been predicted using ab initio SCF/6–31G(d, p) calculations and DFT (BLYP) calculations with 6–31G(d, p) and 6–31++G(d, p) basis sets. The changes in the vibrational characteristics from free monomers to a complex have been calculated. The ab initio and BLYP calculations show that the complexation between Vitamin C and five water molecules leads to large red shifts of the stretching vibrations for the monomer bonds involved in the hydrogen bonding and very strong increase in their IR intensity. The predicted frequency shifts for the stretching vibrations from Vitamin C taking part in the hydrogen bonding are up to −508 cm −1. The magnitude of the wavenumber shifts is indicative of relatively strong OH···H hydrogen-bonded interactions. In the same time the IR intensity and Raman activity of these vibrations increase upon complexation. The IR intensity increases dramatically (up to 12 times) and Raman activity increases up to three times. The ab initio and BLYP calculations show, that the symmetric OH vibrations of water molecules are more sensitive to the complexation. The hydrogen bonding leads to very large red shifts of these vibrations and very strong increase in their IR intensity. The asymmetric OH stretching vibrations of water, free from hydrogen bonding are less sensitive to the complexation than the hydrogen-bonded symmetric O H stretching vibrations. The increases of the IR intensities for these vibrations are lower and red shifts are negligible.

Polymorphic phase transition in Superhydrous Phase B

We synthesized superhydrous phase B (shy-B) at 22 GPa and two different temperatures: 1200°C (LT) and 1400°C (HT) using a multi-anvil apparatus. The samples were investigated by transmission electron microscopy (TEM), single crystal X-ray diffraction, Raman and IR spectroscopy. The IR spectra were collected on polycrystalline thin-films and single crystals using synchrotron radiation, as well as a conventional IR source at ambient conditions and in situ at various pressures (up to 15 GPa) and temperatures (down to −180°C). Our studies show that shy-B exists in two polymorphic forms. As expected from crystal chemistry, the LT polymorph crystallizes in a lower symmetry space group (Pnn2), whereas the HT polymorph assumes a higher symmetry space group (Pnnm). TEM shows that both modifications consist of nearly perfect crystals with almost no lattice defects or inclusions of additional phases. IR spectra taken on polycrystalline thin films exhibit just one symmetric OH band and 29 lattice modes for the HT polymorph in contrast to two intense but asymmetric OH stretching bands and at least 48 lattice modes for the LT sample. The IR spectra differ not only in the number of bands, but also in the response of the bands to changes in pressure. The pressure derivatives for the IR bands are higher for the HT polymorph indicating that the high symmetry form is more compressible than the low symmetry form. Polarized, low-temperature single-crystal IR spectra indicate that in the LT-polymorph extensive ordering occurs not only at the Mg sites but also at the hydrogen sites.

Structures of [Mg · (H 2O) 1,2] + and [Al · (H 2O) 1,2] + ions studied by infrared photodissociation spectroscopy: evidence of [HO–Al–H] + ion core structure in [Al · (H 2O) 2] +

Infrared spectra of [Mg · (H 2O) 1,2] + and [Al · (H 2O) 1,2] + are measured in the OH stretching region (3200–3800 cm −1). The spectra show the symmetric and asymmetric OH stretching bands of water molecules that are directly bound to the metal ions through metal–oxygen intermolecular bonds. In addition to these bands, the [Al · (H 2O) 2] + ion has another band at 3714 cm −1. This band is assigned to the free OH stretching vibration of the [HO–Al–H] + ion; the aluminum ion is inserted into the O–H bond of one water molecule in [Al · (H 2O) 2] +.

IR absorption spectroscopy of water in CsLiB6O10 crystals

AbstractPolarized absorption spectra of CsLiB 6 O 10 crystals have been measured between )186 and 25 C in the 1500–7500cm 1 wavenumber range. A series of absorption bands have been observed with intensities depending on the thermalhistory of the crystals. Three of them have been assigned as the fundamental H–O–H bending mode (d ¼ 1650 cm 1 ),and symmetric and asymmetric OH stretching modes of the bound H 2 O molecule (m s ¼ 3413 cm 1 and m a ¼ 3581 cm 1 ,respectively). Additional features in the 3800–4400, 4700–5300 and 6500–7100 cm 1 ranges have been interpreted asovertones and combinations of the fundamental H 2 O vibrations. The above assignments have been verified by detectingthe isotopic replica of the bands in a crystal treated in D 2 O vapour atmosphere. The possible sites for the H 2 O moleculein the lattice have been deduced from polarization angle dependence measurements. 2003 Elsevier B.V. All rights reserved. PACS: 42.70.Mp; 61.72.)y; 78.30.HvKeywords: FTIR spectroscopy; H

Infrared Spectroscopic Characterization of the Symmetrical Hydration Motif in the ·H2O Complex

We report for the first time the vibrational spectrum of a molecular anion−water complex in which the water molecule adopts a symmetrical binding motif. In the specific complex considered, S ·H2O, each hydrogen atom is attached to one of the oxygen atoms of the anion. The vibrational spectrum is rather simple and is analyzed with the aid of isotopic substitution and ab initio calculations of the complex structure and harmonic vibrational frequencies. The symmetric and asymmetric OH stretching modes in the S ·H2O complex are much closer in energy than in the isolated water molecule, an effect that is traced to the reduction in the HOH angle of the water molecule upon complexation.

Infrared Photodissociation Spectroscopy of Protonated Formic Acid−Water Binary Clusters, H+·(HCOOH)n·H2O (n = 1−5). Spectroscopic Study of Ion Core Switch Model and Magic Number

Infrared spectra of protonated formic acid−water binary clusters, H+·(HCOOH)n·H2O (n = 1−5), are investigated by infrared photodissociation spectroscopy and ab initio molecular orbital calculations. The asymmetric OH stretching vibration of water is observed in the infrared photodissociation spectra of the clusters with n = 1−3; it disappears in the spectra of the n = 4 and 5 clusters. On detailed comparison of the observed infrared spectra with calculated ones, the most stable geometric structures are obtained for the n = 1−5 clusters. These results suggest that the clusters switch the ion cores from HCOOH2+ for n = 1−3 to H3O+ for n = 4 and 5. The n = 5 cluster has a cyclic-type structure; the H3O+ ion core is fully surrounded and stabilized by five formic acid molecules. This characteristic nature produces a magic number of the n = 5 cluster.

Quantum dynamics of methanol: Hamiltonian, representation and intensity considerations

Employing a body-fixed axis system and Jacobi coordinates, a model for the vibration–torsion–rotation Hamiltonian of the CH 3OH molecule with large-amplitude internal motions has been derived. This Hamiltonian is expressed in terms of Jacobi coordinates and is partitioned in the form H A+ H B+ H int, where H A and H B are the rovibrational Hamiltonians of methyl group CH 3 and asymmetric rotor OH, and H int represents their interactions. The resulting Hamiltonian is used to carry out a pure quantum mechanical calculation for this kind of molecule or to construct the potential surface using observed data. The detailed discussion of the Hamiltonian is presented for the model with a rigid methyl group and a rigid OH, which describes five lower frequency vibrational modes and pure rotation in the molecule. We discuss the advantages of body-fixed Jacobi form of the Hamiltonian and solution strategies for practical programming. The properties of labels of the energy states, potential function and dipole moments are investigated according to the molecular symmetry group G 6 of methanol. Finally, the developed formulation is used to calculate the energy levels of CO-stretching–torsion–rotation for lower rotational excitation ( J⩽5). Comparison of the calculated results with experimental ones is presented.

Vibrational spectra of the methanol tetramer in the OH stretch region. Two cyclic isomers and concerted proton tunneling

Second order Mo/ller–Plesset perturbation theory and density functional theory are employed to localize several stationary points on the potential energy surface of the cyclic methanol tetramer. Two cyclic isomers are identified: one of S4 symmetry, with methyl groups in up-down-up-down configuration, and a second one of Ci symmetry, with the methyl groups in up-up-down-down configuration. The latter minimum is 360 cm−1 above the S4 minimum, with a barrier of 475 cm−1 separating them. These isomers give rise to four asymmetric OH modes around 3300 cm−1. A model of the concerted proton transfer, S4→D2d→S4 (D2d is the transition structure), yields an estimate of 0.7 cm−1 for the tunneling splitting of the totally symmetric OH stretch vibrational fundamental. Raman spectra would show evidence of this fundamental and help to identify admixtures of the Ci isomer.

Vibration, rotation, and parity specific predissociation dynamics in asymmetric OH stretch excited ArH2O: A half collision study of resonant V–V energy transfer in a weakly bound complex

Para ArH2O complexes are detected via slit jet direct absorption spectroscopy using continuous wave difference frequency generation of high resolution tunable IR in the 3780 cm−1 v3=1←0 asymmetric OH stretch region. P/R and Q branch transitions on the Π(101,v3=1)←Σ(000,v3=0) band are observed, which derive oscillator strength from the 101←000 v3=1←0 transition in free H2O and access upper states of e and f parity, respectively. Frequency shifts in the f parity levels (Q branch), and both frequency shifts and predissociation broadened linewidths in the e parity levels (P/R branch) are evidenced in the spectrum, unambiguously characteristic of an avoided crossing in the vicinity of J′=6 with a second, near resonant vibration–internal rotation state in ArH2O. From detailed analysis of the avoided crossing, this perturbing state is assigned to a symmetric (v1=1) OH stretch+internal rotor state in ArH2O, which resonantly mixes with the IR laser prepared asymmetric (v3=1) OH stretch by resonant ‘‘half collisional’’ V→V transfer with the Ar atom. The striking parity dependence of the observed predissociation linewidths results from energy conservation and the symmetries of the asymptotic Ar+H2O (v1=1) states; the e parity levels can dissociate to the ground 000 rotor level of H2O (v1=1), whereas the f parity levels can access at lowest the 111 rotor level, therefore releasing insufficient energy to rupture the van der Waals bond. The data establishes a clear upper limit on the dissociation bond strength for para ArH2O, and place spectroscopic constraints on the promoting internal rotor state in ArH2O (v1=1). A simple local mode theory of half collision induced mixing between symmetric and asymmetric stretch excitation in H2O is presented. The model predicts a coupling which is proportional to three factors, (i) a ‘‘steric’’ term which describes the overlap of initial/final internal rotor wave functions in the ArH2O angular geometry conductive to energy transfer, (ii) a ‘‘collisional’’ term which depends on the van der Waals stretching frequency and reduced mass, and (iii) an intramolecular V→V term to describe the ‘‘rephasing’’ of the OH local modes that characterizes the collisional transformation between asymmetric and symmetric stretch vibrations. All the parameters in the model are accessible from the high resolution van der Waals spectra, and the resulting predictions are in surprisingly good agreement with the coupling spectroscopically determined from the perturbation analysis. The high efficiency of the predissociation dynamics is also qualitatively consistent with the near gas kinetic v3↔v1 energy transfer observed by Finzi et al. [J. Chem. Phys. 63, 2285 (1975)] in thermally averaged H2O(v1,v3)+Ar collisions. In summary, analysis of the J and parity dependent predissociation linewidths and frequency shifts in a van der Waals near-IR spectrum of ArH2O offers an unusually detailed glimpse at collision induced intramolecular V–V transfer in vibrationally excited H2O from a half collision perspective.

VLA observations of the OH emission from Comet Wilson (1986) - The value of high resolution in both spatial and velocity coordinates

In comparison with Comet Halley, the radio OH emission from Comet Wilson behaved very erratically, changing rapidly in position as well as in velocity, while the emission and brightness distribution from Comet Halley displayed apparent stability. A few months later, nearer perihelion, just the opposite behavior was observed at UV wavelengths. Another difference between the two comets is that the OH emission from Comet Halley seemed confined to a region a few times 100.000 km in size, while the emission from Comet Wilson showed up in sporadic blobs, with variable intensities and velocities, at distances as far as 10 to the 6th km from the nucleus. This behavior in Comet Wilson may be associated with the disintegration of the outer frosting associated with new comets and possibly with the fragmentation and ejection of cometesimals from the nucleus. As part of the data analysis, it is demonstrated that lengthening the integration time and lowering the velocity resolution affects the symmetry of the OH images and spectral-line profiles. As a consequence, asymmetric cometary OH line profiles may be more common than previously thought.

Asymmetric circumstellar OH maser emission: effect of density fluctuations

Les asymetries dans les profils de la raie maser OH 1612 MHz sont etudiees en termes de fluctuations de densite dans l'enveloppe circumstellaire. Le spectre integre et la distribution spatiale de l'emission maser sont calcules pour un modele d'enveloppe circumstellaire avec des condensations de densite. L'asymetrie du profil est analyse dans un echantillon d'etoiles OH/IR avec les flux IRAS disponibles

Etude vibrationnelle de la phase II des hydrogénodisulfates de triammonium, (NH 4) 3H(SO 4) 2 et (ND 4) 3D(SO 4) 2

The i.r. and Raman spectra of room temperature phase (phase II) of (NH 4) 3H(SO 4) 2 and (ND 4) 3D(SO 4) 2 as polycrystalline samples and single crystals have been investigated between 4000 and 30 cm −1. An assignment of internal and external modes is given in terms of group frequencies and symmetry types. This crystal contains non-centrosymmetric dimers (SO 4HSO 4) 3− where sulphate ions are associated by strong asymmetric OH … O hydrogen bonds; they are characterized by two strong Raman bands at 1078 and 966 cm −1, and a νOH frequency at about 1250 cm −1. The acidic proton is statistically disordered around the crystallographic symmetry centre while all of the NH + 4 ions show an important dynamical orientational disorder.

Vibrational spectra and valence force field calculation of deltic acid

Infrared and Raman spectra of crystalline deltic acid and its deuterated derivative have been studied between 4000 and 20 cm −1. In order to specify vibrational assignment of ring and CO modes based on C 2v molecular symmetry, valence force field calculation was undertaken. It appears that the results obtained for simpler disubstituted cyclopropenones can be applied to deltic acid. So, the highest frequencies about 1930 and 1610 cm −1 involve nearly equal mixture of ring and CO stretching. Two different, strong but asymmetric OH ▪OC hydrogen bonds occur in crystal.

Solvent effect on acid salt of dichloroacetic acid containing short and asymmetric OH…O bond

The IR and 1H NMR spectra are reported for tetra-n-butylammonium bis-dichloroacetate in five dry aprotic solvents of different polarity (ε=2.27 – 64.4) and basicity (DN= 0.1 – 15.1). Both the integrated intensity (A) and the centre of gravity ( ν ) of continuous absorption show weak dependence upon solvent used. The chemical shift (δ) depends on the proton acceptor properties of solvents and is consistent with an equilibrium (BU) 4NA + AH ⇌ (BU) 4N(AHA). The weak dependence of A and ν upon the solvent polarity is consistent with the single minimum energy surface postulated in the literature for the strong OHO bonds.

Étude vibrationnelle des acides deltiques C3O3H2 et C3O3D2

The infrared and Raman spectra of crystalline deltic acid and its deuterated derivative have been investigated in the 4000–20[Formula: see text]cm−1 range. An assignment of all the intramolecular fundamentals has been proposed assuming a C2v molecular symmetry. The crystal symmetry is likely to be described by the [Formula: see text] or P2/m space group with Z = 2. Deltic acid molecules probably form infinite chains linked with two very strong, asymmetric, and different OH … O hydrogen bonds, with O … O distances estimated at 2.49 and 2.56 Å.

Spectres de vibration des oxalates acides de sodium: Effet isotopique sur la liaison hydrogéne

The infrared and Raman spectra of crystalline hydrogen oxalates, NaHC 2O 4, NaHC 2O 4·H 2O and NaDC 2·D 2O have been investigated in the 4000–30 cm −1 range. An assignment of the observed internal and external fundamentals is given. A tentative interpretation of three broad bands near 2450, 1880 and 1550 cm −1 due to a strong and asymmetric OH⋯O hydrogen bond is proposed and the temperature effect on these bonds is discussed. The isotope effect on the OH stretching frequency is compared to the X-ray data.