Reaction of water with Ce-Au(1 1 1) and CeOx/Au(1 1 1) surfaces: Photoemission and STM studies

This article reports photoemission and STM studies for the adsorption and dissociation of water on Ce-Au(1 1 1) alloys and CeO_x/Au(1 1 1) surfaces. In general, the adsorption of water at 300 K on disordered Ce-Au(1 1 1) alloys led to O-H bond breaking and the formation of Ce(OH)_x species. Heating to 500-600 K induced the decomposition or disproportionation of the adsorbed OH groups, with the evolution of H₂ and H₂O into gas phase and the formation of Ce₂O₃ islands on the gold substrate. The intrinsic Ce ↔ H₂O interactions were explored by depositing Ce atoms on water multilayers supported on Au(1 1 1). After adsorbing Ce on ice layers at 100 K, the admetal was oxidized immediately to yield Ce³⁺. Heating to room temperature produced finger-like islands of Ce(OH)_x on the gold substrate. The hydroxyl groups dissociated upon additional heating to 500-600 K, leaving Ce₂O₃ particles over the surface. On these systems, water was not able to fully oxidize Ce into CeO₂ under UHV conditions. A complete Ce₂O₃ → CeO₂ transformation was seen upon reaction with O₂. The particles of CeO₂ dispersed on Au(1 1 1) did not interact with water at 300 K or higher temperatures. In this respect, they exhibited the same reactivity as does a periodic CeO₂(1 1 1) surface. On the other hand, the Ce₂O₃/Au(1 1 1) and CeO_2−x/Au(1 1 1) surfaces readily dissociated H₂O at 300-500 K. These systems showed an interesting reactivity for H₂O decomposition. Water decomposed into OH groups on Ce₂O₃/Au(1 1 1) or CeO_2−x/Au(1 1 1) without completely oxidizing Ce³⁺ into Ce⁴⁺. Annealing over 500 K removed the hydroxyl groups leaving behind CeO_2−x/Au(1 1 1) surfaces. In other words, the activity of CeO_x/Au(1 1 1) for water dissociation can be easily recovered. The behavior of gold-ceria catalysts during the water-gas shift reaction is discussed in light of these results.     

Adsorption and reaction of methanol on thin-film cerium oxide

Methanol adsorption and reaction has been studied on cerium oxide thin films that were vapor deposited on Ru(0 0 0 1). The methanol behavior was examined as a function of temperature and Ce oxidation state. Methanol reacts at low temperatures with fully oxidized CeO₂ to produce water at 200 K while formaldehyde and methanol desorb near 560 K. This leads to the reduction of the ceria. On reduced ceria, more methanol can be adsorbed and it undergoes more extensive decomposition producing CO and H₂ near 640 K in addition to formaldehyde and water. As the degree of ceria reduction increases, more H₂ and less H₂O are produced. TPD experiments using isotopically labeled CH₃OD show that deuterated water is produced from the oxidized surface at low temperatures, whereas the deuterium is stabilized on the reduced surface and is incorporated into the dihydrogen that desorbs near 600 K. High resolution C 1s and O 1s XPS and C k-edge NEXAFS measurements were performed to quantify the amount of methanol adsorbed and to identify the adsorbed species.     

Inhibition of iron corrosion in 0.5 M sulphuric acid by metal cations

Corrosion inhibitors are widely used in acid solutions during pickling and descaling. Mostly organic compounds containing N, O, and S groups are employed as inhibitors. In this study, the inhibition performance of metal cations such as Zn²⁺, Mn²⁺ and Ce⁴⁺ ions in the concentration range 1-10 × 10⁻³ M has been found out. The corrosion behaviour of iron in 0.5 M H₂SO₄ in the presence of metal cations is studied using polarization and impedance methods. It is found that the addition of these metal cations inhibits the corrosion markedly. The inhibition effect is in the following order Ce⁴⁺ ? Mn²⁺ > Zn²⁺.     

Synthesis and performance of Y-doped La0.7Sr0.3CrO3−δ as a potential anode material for solid oxygen fuel cells

Y-doped La_0.7Sr_0.3CrO_3−δ is a promising anode catalyst for solid oxygen fuel cell (SOFC). The performances of chemical and physical are measured by SEM, XRD and FT-IR. The conductivities of catalyst are measured by DC four-probe method in 20% H₂S-N₂, 3% H₂-N₂ and air from 573 K to 1173 K, respectively. The results show that Y-doped La_0.7Sr_0.3CrO_3−δ powders have perfect perovskite phase structure with no extra peaks and exhibit good chemical compatibility with Ce_0.8Sm_0.2O_1.9 (as electrolyte) in air. Through XRD and FT-IR analysis no sulfur-containing species is detected after exposure to the 20% H₂S at 1173 K for 5 h. Meanwhile, Y-doped La_0.7Sr_0.3CrO_3−δ shows that the highest conductivity is 0.21 S/cm at 1173 K in H₂S. The open circuit voltages are 0.85 V at 1173 K in H₂S and 1.04 V at 823 K in H₂. The maximal power densities are 12.4 mW/cm² in H₂S and 1.59 W/cm² in H₂ for cells comprising Y-doped La_0.7Sr_0.3CrO_3−δ-Sm_0.2Ce_0.8O_1.9/Sm_0.2Ce_0.8O_1.9/Ag.     

Weak water absorption lines around 1.455 and 1.66 μm by CW-CRDS

The absorption spectra of water vapor near 1.455 and 1.66 μm have been recorded with a typical absorption sensitivity of 5 × 10⁻¹⁰ cm⁻¹ by using CW-cavity ring down spectroscopy. A series of 18 distributed feed-back (DFB) lasers was used as sources and allowed for the coverage of the 5911.0-5922.5, 5926-5941.8, 5957.0-6121.6, and 6745-7015.6 cm⁻¹ spectral regions. These regions extend to lower and higher energies our previous study of the water spectrum in the important 1.5 μm transparency window [P. Macko, D. Romanini, S.N. Mikhailenko, O.V. Naumenko, S. Kassi, A. Jenouvrier, Vl.G. Tyuterev, J. Mol. Spectrosc. 227 (2004) 90-108]. The line parameters were determined with the help of an interactive least squares multi-lines fitting program which uses a Voigt function as line profile. More than 1900 water lines with intensities ranging between 10⁻²⁸ and 5 × 10⁻²⁴ cm/molecule at 296 K were measured, about 690 of them being reported for the first time. The rovibrational assignment was performed on the basis of previously determined energy levels and of the results of the variational global calculations [H. Partridge, D.W. Schwenke, J. Chem. Phys. 106 (1997) 4618-4639]. The assignment results were validated by using the Ritz combination principle together with previously reported water transitions. Several new energy levels were determined for the H₂¹⁶O, H₂¹⁷O, and HD¹⁶O isotopologues. The retrieved line lists of the H₂¹⁶O, H₂¹⁷O, H₂¹⁸O, and HD¹⁶O isotopologues are compared with the available calculated and experimental (FTS) databases for water.     

High sensitivity CW-cavity ring down spectroscopy of water in the region of the 1.5 μm atmospheric window

The absorption spectrum of natural water vapour around 1.5 μm has been recorded with a typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹ by using a CW-cavity ring down spectroscopy set up based on fibred DFB lasers. A series of 31 DFB lasers has allowed a full coverage of the 6130.8-6748.5 cm⁻¹ (1.63-1.48 μm) region corresponding to the H transparency band of the atmosphere. The line parameters (wavenumber and intensity) of a total of 5190 lines, including 4247 lines of water vapor, were derived by a one by one fit of the lines to a Voigt profile. Different isotopologues of water (H₂¹⁶O, H₂¹⁸O, H₂¹⁷O, and HD¹⁶O) present in natural abundance in the sample contribute to the spectrum. For the main isotopologue, H₂¹⁶O, 2130 lines were measured with line intensities as weak as 10⁻²⁹ cm/molecule while only 926 lines (including a proportion of 30% inaccurate calculated lines) with a minimum intensity of 3 × 10⁻²⁷ cm/molecule are provided by the HITRAN and GEISA databases. Our comparison in the whole 5750-7965 cm⁻¹ region, has also evidenced that an error in the process of conversion of the intensity units from cm⁻²/atm to cm⁻¹/(molecule × cm⁻²) at 296 K, has led to H₂¹⁶O line intensities values listed in the HITRAN-2000 database, systematically 8 % below the original FTS values. The rovibrational assignment was performed on the basis of the ab initio calculations by Schwenke and Partridge with a subsequent refinement and validation using the Ritz combination principle together with all previously measured water transitions relevant to this study. This procedure allowed determining 172, 139, 71, and 115 new energy levels for the H₂¹⁶O, H₂¹⁸O, H₂¹⁷O, and HD¹⁶O isotopologues, respectively. The results are compared with the available databases and discussed in regard of previous investigations by Fourier transform spectroscopy. The spectrum analysis has showed that most of the transitions which cannot be assigned to water are very weak and are due to impurities such as carbon dioxide and ammonia, leaving only about 3% of the observed transitions unassigned. The interest of a detailed knowledge of water absorption for trace detectors developed in the 1.5 μm range is underlined: for instance HDO contributes significantly to the considered spectrum while no HDO line parameters are provided by the HITRAN database.     

New measurements of the water vapor continuum in the region from 0.3 to 2.7 THz

We present a spectroscopic study of the water vapor continuum absorption in the far-IR region from 10 to 90 cm⁻¹ (0.3-2.7 THz). The experimental technique combines a temperature-stabilized multipass absorption cell, a polarizing (Martin-Puplett) interferometric spectrometer, and a liquid-He-cooled bolometer detector. The contributions to the absorbance resulting from the structureless H₂O-H₂O and H₂O-N₂ continua have been measured in the temperature range from 293 to 333 K with spectral resolution of 0.04-0.12 cm⁻¹. The resonant water vapor spectrum was modeled using the HITRAN04 database and a Van Vleck-Weisskopf lineshape function with a 100 cm⁻¹ far-wing cut-off. Within experimental uncertainty, both the H₂O-H₂O and H₂O-N₂ continua demonstrate nearly quadratic dependencies of absorbance on frequency with, however, some deviation near the 2.5 THz window. The absorption coefficients of 3.83 and 0.185 (dB/km)/(kPa THz)² were measured for self- and foreign-gas continuum, respectively. The corresponding temperature exponents were found to be 8.8 and 5.7. The theoretically predicted foreign continuum is presented and a reasonable agreement with experiment is obtained.     

High sensitivity ICLAS of H2O in the 12,580-13,550 cm transparency window

High-sensitivity Intracavity Laser Absorption Spectroscopy (ICLAS) is used to measure the high resolution absorption spectrum of H₂¹⁸O between 12,580 and 13,550 cm⁻¹. This spectral region covers the 3v+δ polyad of very weak absorption. Four isotopologues of water (H₂¹⁸O, H₂¹⁶O, H₂¹⁷O, HD¹⁸O) are found to contribute to the observed spectrum. Spectrum analysis is performed with the aid of variational calculations and allowed for assigning 1126 lines belonging to H₂¹⁸O, while only 160 H₂¹⁸O lines are included in the HITRAN-2008 database. Altogether, 823 accurate energy levels of H₂¹⁸O are determined from transitions attributed to 26 upper vibrational states, 438 of them being reported for the first time. New information includes energy levels of four newly observed vibrational states of H₂¹⁸O: (2 4 0), (1 4 1), (0 4 2) and (2 3 1) at 13,167.718, 13,212.678, 13,403.71 and 15,073.975 cm⁻¹, respectively. H₂¹⁸O transitions involving highly excited bending states like (1 6 0), (0 6 1), (0 7 1), (1 7 0), (0 9 0) and even (0 10 0) have been identified as a result of an intensity borrowing from stronger bands via high-order resonance interactions. Thirty-six new energy levels of H₂¹⁷O, present with a 2% relative concentration in our sample, could be determined. The rotational structure of the (0 2 3) state of HD¹⁸O at 13,245.497 cm⁻¹ is also reported for the first time.     

Adsorption of CO and C2H4 on Rh-loaded thin-film dysprosium oxide

A dysprosium oxide thin film was deposited on Ru(0 0 0 1) by vapor depositing Dy in 2 × 10⁻⁷ torr O₂ while the Ru was at 700 K. The film was ca. 5 nm thick and produced a p(1.4 × 1.4) LEED pattern relative to the Ru(0 0 0 1) substrate. The adsorption and reaction of CO and C₂H₄ adsorbed on Rh supported on the Dy₂O₃ film were studied by TPD and SXPS. The CO initially reacted with loosely bound oxygen in the substrate to produce CO₂. After the loosely bound oxygen was removed, the CO adsorbed non-dissociatively in a manner similar to what is seen on Rh(1 1 1). C₂H₄ adsorbed on the Rh particles and underwent progressive dehydrogenation to produce H₂ during TPD. The C from the C₂H₄ reacted with the O in Dy₂O₃ to produce CO. CO dissociation on the Rh particles could be promoted by treating the Dy₂O₃ with C₂H₄ before CO exposure.     

Methanol adsorption on a CeO2(1 1 1)/Cu(1 1 1) thin film model catalyst

Adsorption and desorption of methanol on a CeO₂(1 1 1)/Cu(1 1 1) thin film surface was investigated by XPS and soft X-ray synchrotron radiation PES. Resonance PES was used to determine the occupancy of the Ce 4f states with high sensitivity. Methanol adsorbed at 110 K formed adsorbate multilayers, which were partially desorbed at 140 K. Low temperature desorption was accompanied by formation of chemisorbed methoxy groups. Methanol strongly reduced cerium oxide by forming hydroxyl groups at first, which with increasing temperature was followed by creation of oxygen vacancies in the topmost cerium oxide layer due to water desorption. Dissociative methanol adsorption and creation of oxygen vacancies was observed as a Ce⁴⁺ → Ce³⁺ transition and an increase of the Ce 4f electronic state occupancy.     

Electrical properties and redox stability of tantalum-doped strontium titanate for SOFC anodes

SrTa_xTi_1−xO₃ (STT) with x = 0.01, 0.05, and 0.10, has been investigated as a potential electron conductor for solid oxide fuel cell (SOFC) anodes. STT was found to be chemically stable under oxidizing and reducing conditions and chemically compatible with yttria-stabilized zirconia (YSZ). The coefficient of thermal expansion (CTE) was near that of YSZ, ranging from 11.3 to 11.8 × 10⁻⁶ K⁻¹. The conductive properties of bulk STT and porous STT-YSZ composites were studied under relevant SOFC operating temperatures and redox cycling conditions. In order to achieve reasonable conductivities, samples were initially reduced at 1673 K. Conductivity after redox cycling was higher for lower dopant concentrations. The redox stable conductivity of a porous composite with x = 0.01 was 1.1 S/cm at 1073 K in humidified H₂ (3% H₂O). Fuel cell tests indicated an anode impedance of 0.4 Ω cm² at 973 K in humidified H₂ for STT-YSZ anodes infiltrated with 3 wt.% CeO₂ and 1 wt.% Pd.     

Mixed water/OH structures on Pd(1 1 1)

Chemisorbed O and water react on Pd(1 1 1) at low temperatures to form a mixed OH/H₂O layer with a (√3 × √3)R30° registry. Reaction requires at least two water molecules to each O before the (2 × 2)O islands are consumed, the most stable OH/water structure being a (OH + H₂O) layer containing 0.67 ML of oxygen, formed by the reaction 3H₂O + O → 2(H₂O + OH). This structure is stabilised compared to pure water structures, decomposing at 190 K as OH recombines and water desorbs. The (√3 × √3)R30° − (OH + H₂O) phase cannot be formed by O/H reaction and is distinct from the (√3 × √3)R30° structure formed by O/H coadsorption below 200 K. Mixed OH/water structures do not react with coadsorbed H below 190 K on Pd(1 1 1), preventing this phase catalyzing the low temperature H₂/O₂ reaction which only occurs at higher temperatures.     

Structural, vibrational and dielectric properties of new potassium hydrogen sulfate arsenate: K4(SO4)(HSO4)2(H3AsO4)

A new compound, K₄(SO₄)(HSO₄)₂(H₃AsO₄) was synthesized from water solution of KHSO₄/K₃H(SO₄)₂/H₃AsO₄. This compound crystallizes in the triclinic system with space group P1¯ and cell parameters: a=8.9076(2) Å, b=10.1258(2) Å, c=10.6785(3) Å; α=72.5250(14)°, β=66.3990(13)°, γ=65.5159(13)°, V=792.74(3) Å³, Z=2 and ρ_cal=2.466 g cm⁻³. The refinement of 3760 observed reflections (I>2σ(I)) leads to R₁=0.0394 and wR₂=0.0755. The structure is characterized by SO₄²⁻, HSO₄⁻ and H₃AsO₄ tetrahedra connected by hydrogen bridge to form two types of dimer (H(16)S(3)O₄⁻?S(1)O₄²⁻ and H(12)S(2)O₄⁻?H₃AsO₄). These dimers are interconnected along the [1¯ 1 0] direction by the hydrogen bonds O(3)-H(3)?O(6). They are also linked by the hydrogen bridge assured by the hydrogen atoms H(2), H(3) and H(4) of the H₃AsO₄ group to build the chain S(1)O₄?H₃AsO₄ which are parallel to the “a” direction. The potassium cations are coordinated by eight oxygen atoms with K-O distance ranging from 2.678(2) to 3.354(2) Å.Crystals of K₄(SO₄)(HSO₄)₂(H₃AsO₄) undergo one endothermic peak at 436 K. This transition detected by differential scanning calorimetry (DSC) is also analyzed by dielectric and conductivity measurements using the impedance spectroscopy techniques. The obtained results show that this transition is protonic by nature.     

Low-uncertainty H2O line intensities for the 930-nm region

We measured room-temperature H₂O spectra of the 3ν polyad within the wave number range 10 603 cm⁻¹ to 10 852 cm⁻¹ using frequency-stabilized cavity ring-down spectroscopy. More than 70 transitions, divisible into two groups based on their relative intensities (strong and weak) were investigated. For the 23 lines comprising the set of strong transitions, the water vapor sample was prepared as a dilute mixture in a steady flow of N₂ carrier gas, and the measurement of the water vapor sample number density was linked to primary methods of humidity generation. For these strong transitions, the measured line intensities were within 1% of previous measurements. The line intensity measurements of the weaker H₂O transitions, were made on samples of static pure water vapor, and these results were systematically greater than previous measurements by approximately 20%.     

Oxidation of Zircaloy-4 by H2O followed by molecular desorption

The interaction of H₂O with Zircaloy-4 (Zry-4) is investigated using Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) methods. Following adsorption of H₂O at 150 K the Zr(MNV) and Zr(MNN) Auger features shift by ∼6.5 and 4.5 eV, respectively, indicating surface oxidation. Heating H₂O/Zry-4 results in molecular desorption of water at both low and high temperatures. The low-temperature desorption is attributed to ice multilayers, whereas, three overlapping high-temperature features are presumably due to recombinative desorption. This high-temperature desorption begins before the surface oxide is dissolved, continues upon its removal, and is atypical for water/metal systems. Unexpectedly, no significant desorption of hydrogen is observed near 400 K, as is typically observed following O₂ adsorption on Zr-based materials. However, we do observe that H₂O adsorption on Zry-4 surfaces roughened by argon ion sputtering results in H₂ desorption.     

Magnetic susceptibility study of Ce in PbCeA (A=Te,Se, S)

The magnetic susceptibility of Pb_1-xCe_xA (A=S, Se and Te) crystals with Ce³⁺ concentrations 0.006≤x≤0.036 was investigated in the temperature range from 2 K to 300 K. The magnetic susceptibility data was found to be consistent with a ²F_5/2 lowest manifold for Ce³⁺ ions with a crystal-field splitting Δ=E(Γ₈)−E(Γ₇) of about 340 K, 440 K and 540 K for Pb_1-xCe_xTe, Pb_1-xCe_xSe, and Pb_1-xCe_xS, respectively. For all the three compounds the doublet Γ₇ lies below the Γ₈ quadruplet which confirms the substitution of Pb²⁺ by Ce³⁺ ions in the host crystals. The observed values for the crystal-field splitting are in good agreement with the calculated ones based on the point-charge model. Moreover, the effective Landé factors were determined by X-band (∼9.5 GHz), electron paramagnetic measurements (EPR) to be g=1.333, 1.364, and 1.402 for Ce ions in PbA, A = S, Se and Te, respectively. The small difference with the predicted Landé factor g of 10/7 for the Γ₇ (J=5/2) ground state was attributed to crystal-field admixture.     

Magnetic properties of the intermetallic compound Ce5Ge4

Magnetic and magnetocaloric properties of the compound Ce₅Ge₄ have been studied. This compound has orthorhombic Sm₅Ge₄-type structure (space group Pnma, no. 62) and orders ferromagnetically at ~12 K (T_C). The paramagnetic Curie temperature is ~−20 K suggesting the presence of competing ferromagnetic and antiferromagnetic interactions in this compound. The magnetization does not seem to saturate even in fields of 90 kOe at 3 K consistent with the presence of competing interactions. Saturation magnetization value (extrapolated to 1/H→0) of only 0.8μ_B/Ce³⁺ is obtained compared to the free ion value of 2.14μ_B/Ce³⁺. This moment reduction in the ordered state of Ce₅Ge₄ could be due to partial antiferromagnetic/paramagnetic ordering of the Ce moments and may also be due to crystalline electric field effects. Magnetic entropy change near T_C, calculated from the magnetization vs. field data, is found to be moderate with a maximum value of ~9 J/kg/K at ~11 K for a field change of 90 kOe.     

Intralamellar structural modifications related to the proton exchanging in K4Nb6O17 layered phase

Basic structural aspects about the layered hexaniobate of K₄Nb₆O₁₇ composition and its proton-exchanged form were investigated mainly by spectroscopic techniques. Raman spectra of hydrous K₄Nb₆O₁₇ and H₂K₂Nb₆O₁₇·H₂O show significant modifications in the 950-800 cm⁻¹ region (Nb-O stretching mode of highly distorted NbO₆ octahedra). The band at 900 cm⁻¹ shifts to 940 cm⁻¹ after the replacement of K⁺ ion by proton. Raman spectra of the original materials and the related deuterated samples are similar suggesting that no isotopic effect occurs. Major modifications were observed when H₂K₂Nb₆O₁₇ was dehydrated: the relative intensity of the band at 940 cm⁻¹ decreases and new bands seems to be present at about 860-890 cm⁻¹. The H⁺ ions should be shielded by the hydration sphere what preclude the interaction with the layers. Removing the water molecules, H⁺ ions can establish a strong interaction with oxygen atoms, decreasing the bond order of Nb-O linkage. X-ray absorption near edge structure studies performed at Nb K-edge indicate that the niobium coordination number and oxidation state remain identical after the replacement of potassium by proton. From the refinement of the fine structure, it appears that the Nb-Nb coordination shell is divided into two main contributions of about 0.33 and 0.39 nm, and interestingly the population, i.e., the number of backscattering atoms is inversed between the two hexaniobate materials.     

High sensitivity CW-CRDS of O enriched water near 1.6 μm

The absorption spectrum of ¹⁸O enriched water has been recorded by continuous wave cavity ring down spectroscopy between 5905.7 and 6725.7 cm⁻¹ using a series of fibred DFB lasers. The investigated spectral region corresponds to the important 1.55 μm transparency window of the atmosphere where water absorption is very weak. The typical CRDS sensitivity (noise equivalent absorption of 5×10⁻¹⁰ cm⁻¹) allowed for the detection of lines with intensity as low as 10⁻²⁸ cm/molecule while the minimum intensity value provided by HITRAN in the considered spectral region is 1.7×10⁻²⁴ cm/molecule. The line parameters were retrieved with the help of an interactive least squares multi-lines fitting program assuming a Voigt function as line profile. Overall, 4510 absorption lines belonging to the H₂¹⁸O, H₂¹⁶O, HD¹⁸O, HD¹⁶O and H₂¹⁷O water isotopologues were measured. Their intensities range between 3×10⁻²⁹ and 5×10⁻²³ cm/molecule at 296 K and the typical accuracy on the line positions is 1×10⁻³ cm⁻¹. 2074 of the observed lines attributed to H₂¹⁸O, HD¹⁸O and H₂¹⁷O are reported for the first time. The transitions were assigned on the basis of variational calculations resulting in 288, 135 and 38 newly determined rovibrational energy levels for the H₂¹⁸O, HD¹⁸O and H₂¹⁷O isotopologues, respectively. The new data set includes the band origin of the 4ν₂ bending overtone of H₂¹⁸O at 6110.4239 cm⁻¹ and rovibrational levels corresponding to J and K_a values up to 18 and 12, respectively, for the strongest bands of H₂¹⁸O: 4ν₂, ν₁+2ν₂, 2ν₂+ν₃, 2ν₁, ν₁+ν₃, and ν₂+ν₃. The obtained experimental results have been compared to the spectroscopic parameters provided by the HITRAN database and to the recent IUPAC critical review of the rovibrational spectrum of H₂¹⁸O and H₂¹⁷O as well as to variational calculations. Large discrepancies between the 4ν₂ variationally predicted and experimental intensities have been evidenced for the H₂¹⁸O and H₂¹⁶O molecules.     

Interaction of H2O with the RuO2(1 1 0) surface studied by HREELS and TDS

The adsorption of water on a RuO₂(1 1 0) surface was studied by using high-resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). The first thermal desorption peak observed between 350 and 425 K is attributed to molecular water adsorbed on fivefold coordinated Ru_cus sites. Higher coverages of water give rise to TDS peaks between 190 and 160 K, which we attribute to water in the second layer bound to bridge oxygen, and multilayers, respectively. HREELS shows that H₂O chemisorbs on Ru_cus sites through oxygen inducing a slight red shift of the vibrational frequency of O_bridge atoms. Molecular adsorption is also confirmed by the presence of both the scissor and the libration modes showing the expected isotopic shift for D₂O. The water adsorbed on the Ru_cus sites also forms hydrogen bonds with the bridge oxygen indicated by the broad intensity at the lower frequency side of the O-H stretch mode. HREELS and TDS results suggest that on the perfect RuO₂(1 1 0) surface water dissociation is almost negligible.