Spectra Of H2O Research Articles

Near-infrared spectra of H2O under high pressure and high temperature: Implications for a transition from proton tunneling to hopping states

The nature of protons in ice VII up to 368°C and 16GPa was investigated with synchrotron near-infrared spectroscopy. The absorption band of the first OH stretching overtone mode divided into doublet peaks above 5GPa at room temperature, suggesting that proton tunneling occurs at the overtone level. As the temperature increased, the doublet peaks gradually reduced to a singlet. This result implies that thermally activated protons hop between the two potential minima along the oxygen–oxygen axis. A pressure–temperature diagram for the proton state was constructed from the changing band shape of the overtone mode.

How Ions Affect the Structure of Water: A Combined Raman Spectroscopy and Multivariate Curve Resolution Study

Raman spectroscopy in combination with multivariate curve resolution (Raman-MCR) is used to explore the interaction between water and various kosmotropic and chaotropic anions. Raman-MCR of aqueous Na-salt (NaI, NaBr, NaNO3, Na2SO4, and Na3PO4) solutions provides solute-correlated Raman spectra (SC-spectra) of water. The SC-spectra predominantly bear the vibrational characteristics of water in the hydration shell of anions, because Na(+)-cation has negligible effect on the OH stretch band of water. The SC-spectra for the chaotropic I(-), Br(-), and NO3(-) anions and even for the kosmotropic SO4(2-) anion resemble the Raman spectrum of isotopically diluted water (H2O/D2O = 1/19; v/v) whose OH stretch band is largely comprised by the response of vibrationally decoupled OH oscillators. On the other hand, the SC-spectrum for the kosmotropic PO4(3-) anion is quite similar to the Raman spectrum of H2O (bulk). Comparison of the peak positions of SC-spectra and the Raman spectrum of isotopically diluted water suggests that the hydrogen bond strength of water in the hydration shell of SO4(2-) is comparable to that of the isotopically diluted water, but that in the hydration shell of I(-), Br(-), and NO3(-) anions is weaker than that of the latter. Analysis of integrated area of component bands of the SC-spectra reveals ∼80% reduction of the delocalization of vibrational modes (intermolecular coupling and Fermi resonance) of water in the hydration shell of I(-), Br(-), NO3(-), and SO4(2-) anions. In the case of trivalent PO4(3-), the vibrational delocalization is presumably reduced and the corresponding decrease in spectral response at ∼3250 cm(-1) is compensated by the increased signal of strongly hydrogen bonded (but decoupled) water species in the hydration shell. The peak area-averaged wavenumber of the SC-spectrum increases as PO4(3-) < SO4(2-) < NO3(-) < Br(-) < I(-) and indeed suggests strong hydrogen bonding of water in the hydration shell of PO4(3-) anion.

Hydrogen passivation of electron trap in amorphous In-Ga-Zn-O thin-film transistors

We report an experimental evidence that some hydrogens passivate electron traps in an amorphous oxide semiconductor, a-In-Ga-Zn-O (a-IGZO). The a-IGZO thin-film transistors (TFTs) annealed at 300 °C exhibit good operation characteristics; while those annealed at ≥400 °C show deteriorated ones. Thermal desorption spectra (TDS) of H2O indicate that this threshold annealing temperature corresponds to depletion of H2O desorption from the a-IGZO layer. Hydrogen re-doping by wet oxygen annealing recovers the good TFT characteristic. The hydrogens responsible for this passivation have specific binding energies corresponding to the desorption temperatures of 300–430 °C. A plausible structural model is suggested.

Selective Probing of the OH or OD Stretch Vibration in Liquid Water Using Resonant Inelastic Soft-X-Ray Scattering

High-resolution O 1s resonant inelastic x-ray scattering spectra of liquid H2O, D2O, and HDO, obtained by excitation near the preedge resonance show, in the elastic line region, well-separated multiple vibrational structures corresponding to the internal OH stretch vibration in the ground state of water. The energy of the first-order vibrational excitation is strongly blueshifted with respect to the main band in the infrared or Raman spectra of water, indicating that water molecules with a highly weakened or broken donating hydrogen bond are correlated with the preedge structure in the x-ray absorption spectrum. The vibrational profile of preedge excited HDO water is well fitted with 50%±20% greater OH-stretch contribution compared to OD, which strongly supports a preference for OH being the weakened or broken H-bond in agreement with the well-known picture that D2O makes stronger H-bonds than H2O. Accompanying path-integral molecular dynamics simulations show that this is particularly the case for strongly asymmetrically H-bonded molecules, i.e., those that are selected by preedge excitation.

Calibration-free sensor for pressure and H2O concentration in headspace of sterile vial using tunable diode laser absorption spectroscopy

Tunable diode laser absorption measurements of pressure and H2O concentration in the headspace of vials using a distributed-feedback (DFB) diode laser near 1.4 μm are reported. A H2O line located near 7161.41 cm(-1) is selected based on its strong absorption strength and isolation from interference of neighboring transitions. Direct absorption spectra of H2O are obtained for the measurement path as well as the reference path by scanning the laser wavelength. The pressure and H2O vapor concentration in the headspace of a vial are inferred from a differential absorption signal, which is the difference between the measured and the referenced absorbance spectra. This sensor is calibration-free and no purge gas is needed. The demonstrated capability would enable measurements of pressure and H2O concentration in the headspace of vials within 2.21% and 2.86%, respectively. A precision of 1.02 Torr and 390 ppm is found for the pressure and H2O concentration, respectively. A set of measurements for commercial freeze-dried products are also performed to illustrate the usefulness of this sensor.

Atmospheric Compensation in Fourier Transform Infrared (FT-IR) Spectra of Clinical Samples

A new method is proposed for the elimination of the spectral contribution of two atmospheric gases (CO2 and H2O) in Fourier transform infrared (FT-IR) spectra of clinical samples. The algorithm is based on the measurement of reference spectra of H2O followed by an automatic calculation of the spectral contribution of the above-mentioned gases to the sample spectra. Then this contribution is compensated by spectral subtraction. Attenuated total reflectance FT-IR spectra of serum and urine samples in the presence of atmospheric gases were corrected and compared with spectra obtained with an N2 purge. Visual inspection of the spectra as well as calculated noise levels confirmed that the method compensated for the contribution of CO2 and H2O to serum and urine spectra to a great extent. As compared with the correction performed by a commercial software package, the proposed method clearly improved the correction of CO2 and provided similar results for H2O compensation. Correlation values between corrected spectra and those obtained under N2-purged conditions in the fingerprint region were higher than 0.995, and noise values in regions where samples did not absorb confirmed the suitability of the correction. The proposed method is fast, easy, and extensible to other gaseous interferences, devices, and acquisition conditions.

Water–Ionomer Interfacial Interactions Investigated by Infrared Spectroscopy and Computational Methods

Structures for interfacial water condensed in pores and channels of the fluorinated ionomer Nafion from low relative humidity atmosphere were probed through the use of Fourier transform infrared (FTIR) spectroscopy and support from classical and quantum chemical calculations. Modern FTIR spectra of H2O and the O-H stretching region for the deuterium-substituted HOD species interacting at the water-ionomer interface in Nafion exchanged by sodium cations are reported and compared to characteristics observed in the earlier studies that employed a dispersive infrared spectrometer and unspecified spectral resolution. Molecular simulations that examine the orientations of water molecules in the vicinity of ionomer were applied to understand the appearance of multiple free O-H stretching bands and the effect of HOD addition. One computational approach was based on a classical force field model, and the other employed density functional theory (DFT) to investigate atomic-scale interactions of water with regions of different hydrophobicity and charge on a perfluorosulfonate ionomer segment. The results suggest hydrogen bonding stabilizes the types of water-ionomer environments that can lead to multiple free O-H stretching vibrational features in experimental spectra. The studies shed light on the structure of H2O at interfaces inside ion conducting membrane materials and have potential for application in elucidating structure at different types of water interfaces.

Mechanisms of H2O desorption from amorphous solid water by 157-nm irradiation: An experimental and theoretical study

The photodesorption of water molecules from amorphous solid water (ASW) by 157-nm irradiation has been examined using resonance-enhanced multiphoton ionization. The rotational temperature has been determined, by comparison with simulations, to be 425 ± 75 K. The time-of-flight spectrum of H2O (v = 0) has been fit with a Maxwell-Boltzmann distribution with a translational temperature of 700 ± 200 K (0.12 ± 0.03 eV). H(+) and OH(+) fragment ions have been detected with non-resonant multiphoton ionization, indicating vibrationally excited parent water molecules with translational energies of 0.24 ± 0.08 eV. The cross section for water removal from ASW by 7.9-eV photons near 100 K is (6.9 ± 1.8) × 10(-20) cm(2) for >10 L H2O exposure. Electronic structure computations have also probed the excited states of water and the mechanisms of desorption. Calculated electron attachment and detachment densities show that exciton delocalization leads to a dipole reversal state in the first singlet excited state of a model system of hexagonal water ice. Ab Initio Molecular Dynamics simulations show possible desorption of a photo-excited water molecule from this cluster, though the non-hydrogen bonded OH bond is stretched significantly before desorption. Potential energy curves of this OH stretch in the electronic excited state show a barrier to dissociation, lending credence to the dipole reversal mechanism.

Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars usingHerschel-HIFI

Herschel-HIFI spectra of H2O towards low-mass protostars show a distinct velocity component not seen in observations from the ground of CO or other species. The aim is to characterise this component in terms of excitation conditions and physical origin. A velocity component with an offset of ~10 km/s detected in spectra of the H2O 110-101 557 GHz transition towards six low-mass protostars in the 'Water in star-forming regions with Herschel' (WISH) programme is also seen in higher-excited H2O lines. The emission from this component is quantified and excitation conditions are inferred using 1D slab models. Data are compared to observations of hydrides (high-J CO, OH+, CH+, C+, OH) where the same component is uniquely detected. The velocity component is detected in all 6 targeted H2O transitions (Eup~50-250K), and in CO 16-15 towards one source, Ser SMM1. Inferred excitation conditions imply that the emission arises in dense (n~5x10^6-10^8 cm^-3) and hot (T~750K) gas. The H2O and CO column densities are ~10^16 and 10^18 cm^-2, respectively, implying a low H2O abundance of 10^-2 with respect to CO. The high column densities of ions such as OH+ and CH+ (both ~10^13 cm^-2) indicate an origin close to the protostar where the UV field is strong enough that these species are abundant. The estimated radius of the emitting region is 100AU. This component likely arises in dissociative shocks close to the protostar, an interpretation corroborated by a comparison with models of such shocks. Furthermore, one of the sources, IRAS4A, shows temporal variability in the offset component over a period of two years which is expected from shocks in dense media. High-J CO gas detected with Herschel-PACS with Trot~700K is identified as arising in the same component and traces the part of the shock where H2 reforms. Thus, H2O reveals new dynamical components, even on small spatial scales in low-mass protostars.

Infrared spectral radiative properties of high temperature gas with multi-component

The shock layer of high-speed missiles is a highly uneven gas medium with multi-component and high temperature. Its spectral radiation effects degrade and distort the remote sensing images of infrared sensors. The exact numerical calculating method of the shock wave thermal radiation noise has been developed in this paper. With the multi-temperature model and the rectangular grid recursive method of ray tracing, atomic-molecular absorption and emission spectra of CO2, H2O and N2 were obtained along the line of sight along the seeker detectors. Based on image degradation evaluation criteria and the wind tunnel experimental results, how images blurred by the proposed model were verified. The relations between the shock wave thermal radiation noise and flow parameters were also analyzed. For the 3–8μm infrared band, shock wave thermal radiation noise is little effected by flight altitude, and close relations with Mach number, as the empirical formula given.

Infrared molar absorption coefficient of H2O stretching modes in SiO2

Infrared absorption of the H2O stretching modes around 3400cm−1 is commonly used to detect the presence of H2O inside SiO2. Obtaining the exact concentration of water remains difficult since the molar absorption coefficient (ε) is not known. In this work ε is determined for H2O absorbed in sub-atmospheric chemical vapor deposited SiO2 and compared to liquid water. By integration over the whole absorption band width, ε is found to be 7.64±1.08×104M−1cm−2. When considering peak absorption at the absorption band maximum only, the value is ε=139.5±11.8M−1cm−1 which is significantly lower than the literature value of liquid water for which ε=231.66±0.05M−1cm−1. This difference is attributed to the absence of hydrogen bridges between H2O molecules, evidenced by the featureless absorption spectrum of H2O inside SiO2.

Synchronous ATR infrared and NIR-spectroscopy investigation of sepiolite upon drying

A new environmental cell allowing for the independent synchronous collection of the near- and mid-infrared spectra (12,000–600cm−1) in the diffuse reflection and attenuated total reflection (ATR) modes, respectively, is reported. The cell is employed to study in real time the dehydration of the phyllosilicate mineral sepiolite, Mg8Si12O30(OH)4(OH2)4·wH2O, in both its natural form and after in situ deuteration at ambient. The spectra are obtained under dynamic purging with dry N2 and compared to those of the same material conditioned over saturated salt solutions. Sepiolite is an important industrial mineral with a modulated structure of alternating tunnels and ribbons. Its mild drying is associated with pronounced vibrational spectral changes due to the removal of surface and zeolitic H2O and the concomitant structural relaxation of the ribbons. Detailed assignments are provided for the fundamental, combination and overtone spectrum of H2O confined in the tunnels of sepiolite, SiOH groups on the external surface of the particles, and Mg3OH groups in the 2:1 ribbons. The spectra are discussed in comparison to those of palygorskite (modulated phyllosilicate with narrower ribbons and tunnels), talc (trioctahedral magnesian phyllosilicate without modulation) and high-surface area silica. It is demonstrated that sepiolite exhibits three discrete states of zeolitic hydration at ambient temperature: Besides the previously known hydrated (w=7–8) and dry (w=0–1) states which dominate the spectra above 30% and below 3% relative humidity, respectively, a hitherto unknown intermediate (w=4–5) is found in the 3–10% range. The new state is most conveniently identified in the near-infrared by a ν02 Mg3O-H stretching mode at 7205cm−1 (ν01=3686cm−1, X=83.5cm−1) and a characteristic H2O combination band at 5271cm−1 (D2O: 3908cm−1).

Determination of temperature and concentrations of main components in flames by fitting measured Raman spectra

The procedure of deriving flame temperature and major species concentrations by fitting measured Raman spectra in hydrocarbon flames is described. The approach simplifies the calibration procedure to determine temperature and major species concentrations from the measured Raman spectra. The calculations of the Raman spectra are performed using data online positions and cross sections from the current literature. Utilizing all spectral information for deriving temperature and major species concentrations substantially increases accuracy, while interferences can easily be detected and filtered out of the measured spectrum. Temperatures from the separate Raman spectra of N2, H2O, O2, CO2 and CO are systematically compared with each other over the span of more than 1,700 K. The agreement between them is generally better than 100 K. The developed procedure also allows us to determine the mole fractions of the major species with absolute accuracy of ±10 %.

Pressure-broadening of water transitions near 7180 cm−1 by helium isotopes

In this study, pressure-broadening parameters for several H2O transitions near 7180cm−1 are obtained which describe collisions with 3He and 4He. The sensitivity of those parameters to choice of theoretical line profile (Galatry vs. Voigt) is investigated. H2O is an important species in atmospheric chemistry and astronomy. Because of this, basic fundamental research, which explores the nature of the H2O spectrum in the presence of different gases of varying physical properties, can provide useful reference data which can be applied in the fields of atmospheric and planetary remote sensing. Measurements were made using an intensity-modulated laser photoacoustic spectrometer. Results from the present work show that Galatry line profiles, with a constrained narrowing parameter, more accurately describe experimental spectra than Voigt profiles over a wide range of experimental pressure conditions. Average pressure-broadening parameters were found to be 0.0216cm−1/atm and 0.0209cm−1/atm for H2O in 3He and 4He, respectively, and were compared to a literature model for the mass-dependence of line broadening. Specific values were obtained for each transition with nominal combined uncertainties of 2–6%.

Effect of temperature on the fluorescence emission of carbazole-substituted methylcellulose in dilute aqueous solutions

Fluorescent-labeled polymers, carbazole-substituted methylcelluloses (Cz-MCs) were synthesized through a two-step reaction by firstly introducing epoxy group to carbazole, and then reacting with MC. Structure of Cz-MC was characterized by using FTIR, NMR, elemental analysis and UV–vis spectroscopy. Aggregation behavior of Cz-MCs in dilute aqueous solution was investigated by a thermotropic study performed with dynamic laser light scattering. Cz-MCs displayed concentration self-quenching properties of fluorescence spectra both in H2O and DMSO. The temperature effect on the fluorescent emission in dilute aqueous solution was explored. The results showed that the degree of substitution of carbazole and thermal aggregation of Cz-MC contributed to the formation of network structure between the molecules, consequently leading to the enhancement or quenching in fluorescence intensity.

The Water Combination Band Reports Solute-Induced Changes in the Dynamic Structure of Bulk Water

The bend+libration combination band in the infrared spectrum of H2O has important consequences for IR spectra of aqueous samples and for the dynamics of bulk water. The combination band has been shown to respond to solutes and even solvated proteins, complicating baseline subtractions in the region from 1900-2400 cm-1 that is the frequent target of biomolecule-based vibrational probe groups. Due to the less prominent and broad shape of this band, it has been largely overlooked in IR studies of water behavior and dynamics.

Infrared diode laser spectroscopy of H2O–CO2 and D2O–CO2 complexes in the v2 bend region of water

The rovibrational spectrum of H2O–CO2 and D2O–CO2 weakly bound complexes has been measured in the v2 bend region of the water monomer by infrared diode laser absorption spectroscopy. Rotational and centrifugal distortion constants for different internal rotation states in the excited vibrational state have been determined. The band-origin of the spectrum is blue-shifted from that of the water monomer by 0.739cm−1 for H2O–CO2 and 0.083cm−1 for D2O–CO2, respectively. The tunneling splitting is reduced upon vibrational excitation by 0.00698(31)cm−1 for H2O–CO2 and 0.00044(17)cm−1 for D2O–CO2, respectively.

Terahertz free-electron laser radiation to determine water concentration in flames

The possibility of measuring the concentration of H2O molecules in flames based on the absorption of terahertz free-electron laser radiation was studied. These measurements were performed using the 177.32 cm−1 absorption line in the rotational spectrum of H2O. This line has a low intensity at room temperature, and at about 1000 K, its intensity is comparable to that of the strongest lines. The temperature dependence of the radiation absorption coefficient at a frequency of 77.32 cm−1 was studied theoretically and experimentally. It is shown that the method can be used for measurements in a sooty C2H4/O2/Ar flame, which strongly scatters visible and UV radiation.

Water in star-forming regions withHerschel: highly excited molecular emission from the NGC 1333 IRAS 4B outflow

During the embedded phase of pre-main sequence stellar evolution, a disk forms from the dense envelope while an accretion-driven outflow carves out a cavity within the envelope. Highly excited H2O emission in spatially unresolved Spitzer/IRS spectra of a low-mass Class 0 object, NGC 1333 IRAS 4B, has previously been attributed to the envelope-disk accretion shock but could instead be produced in an outflow. As part of the survey of low-mass sources in the Water in Star Forming Regions with Herschel (WISH-LM) program, we used Herschel/PACS to obtain a far-IR spectrum and several Nyquist-sampled spectral images with to determine the origin of excited H2O emission from NGC 1333 IRAS 4B. The spectrum has high signal-to-noise in a rich forest of H2O, CO, and OH lines, providing a near-complete census of far-IR molecular emission from a Class 0 protostar. The excitation diagrams for the three molecules all require fits with two excitation temperatures, indicating the presence of two physical components. The highly excited component of H2O emission is characterized by subthermal excitation of 1500 K gas with a density of 10^5 - 10^7 cm-3, conditions that also reproduce the mid-IR H2O emission detected by Spitzer. On the other hand, a high density, low temperature gas can reproduce the H2O spectrum observed by Spitzer but underpredicts the H2O lines seen by Herschel. Nyquist-sampled spectral maps of several lines show two spatial components of H2O emission, one centered at 1200 AU south of the central source at the position of the blueshifted outflow lobe and a second centered on-source. Both spatial components of the far-IR H2O emission are consistent with emission from the outflow. The gas cooling from the IRAS 4B envelope cavity walls is dominated by far-IR H2O emission, in contrast to stronger [O I] and CO cooling from more evolved protostars. [one sentence truncated]

Investigation of an energy-gap model for photoacoustic O2A-band spectra: H2O calibration near 7180 cm−1

A photoacoustic spectrometer is used to evaluate the accuracy of an energy-gap model for collisional energy transfer. For photoacoustic measurements involving the b1Σg+←X3Σg- transition of molecular oxygen the conversion of photon energy to thermal energy is inefficient and proceeds through the a1Δg state. This results in attenuation of the photoacoustic signal. The magnitude of the attenuation can be predicted with an energy-gap model whose accuracy has been previously confirmed to within 3±5%. However, this prior result does not rule out incomplete rotational relaxation of O2 in the a1Δg state. In this study, high-resolution spectra of H2O in air are used to calibrate the photoacoustic spectrometer. This work binds the relative uncertainty in the energy-gap relaxation factor for O2A-band photoacoustic signals to be approximately 1%. During one acoustic cycle, this result implies negligible collisional relaxation to the X3Σg- state of O2 and nearly complete collisional relaxation to the a1Δg state.