Showing papers on "Infrared spectroscopy published in 1996"

Synthesis and Characterization of Hydrophobic, Organically-Soluble Gold Nanocrystals Functionalized with Primary Amines

Abstract: We report on the synthesis and characterization of 25−70 A diameter amine-capped gold nanocrystals. In particular, we show how these particles can be prepared by a simple procedure and confirm the particle composition (including the identity of the amine surface passivant) through several materials characterization techniques that include infrared spectroscopy, nuclear magnetic resonance spectroscopy, ultraviolet−visible spectroscopy, mass spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction analysis, differential scanning calorimetry, thermogravimetric analysis, and elemental analysis. All physical characterizations are consistent with a charge−neutral amine/gold surface interaction described by a weak covalent bond. The stability of the particles appears to be largely kinetic, rather than thermodynamic, in nature. Comparison of these nanocrystals to amines adsorbed onto bulk Au surfaces indicates that the stability of the nanocrystal/amine system is a finite-size effect.

Specific Intermolecular Interaction of Carbon Dioxide with Polymers

Abstract: Fourier transform IR spectroscopy has been used to investigate the interaction of carbon dioxide with polymers. IR transmission and attenuated total reflectance spectra were obtained for CO2 impregnated into polymer films. It has been shown that the polymers possessing electron-donating functional groups (e.g., carbonyl groups) exhibit specific interactions with CO2, most probably of Lewis acid−base nature. An unusual aspect is the use of the bending mode (ν2) of CO2 to probe polymer−CO2 interactions. The evidence of the interaction is the observation of the splitting of the band corresponding to the CO2 ν2 mode. This splitting indicates that the double degeneracy of the ν2 mode is removed due to the interaction of electron lone pairs of the carbonyl oxygen with the carbon atom of the CO2 molecule. This splitting has not been observed for polymers lacking electron-donating functional groups (e.g., poly(ethylene)). In contrast, the ν3 mode shows little if any sensitivity to this interaction, which is in ac...

Infrared spectroscopy of biomolecules

Abstract: Theoretical Analyses of the Amide I Infrared Bands of Globular Proteins (H. Torii & M. Tasumi). Fourier Transform Infrared Spectroscopy of Enzyme Systems (J. Alben). Light--Induced Fourier Transform Infrared Difference Spectroscopy of the Primary Electron Donor in Photosynthetic Reaction Centers (E. Nabedryk). Equipment: Slow and Fast Infrared Kinetic Studies (F. Siebert). Ultrafast Infrared Spectroscopy of Biomolecules (B. Cohen & R. Hochstrasser). Infrared Spectroscopy of Nucleic Acids (J. Liquier & E. Taillandier). Fourier Transform Infrared Spectroscopy in the Study of Hydrated Lipids and Lipid Bilayer Membranes (R. Lewis & R. McElhaney). Fourier Transform Infrared Spectroscopic Studies of Cell Surface Polysaccharides (K. Brandenburg & U. Seydel). Fourier Transform Infrared Spectroscopy of Biomembrane Systems (P. Haris & D. Chapman). What Can Infrared Spectroscopy Tell Us About the Structure and Composition of Intact Bacterial Cells? (D. Naumann, et al.). Biomedical Infrared Spectroscopy (M. Jackson & H. Mantsch). New Trends in Isotope--Edited Infrared Spectroscopy (H. Fabian, et al.). Index.

Potential-Dependent Reorientation of Water Molecules at an Electrode/Electrolyte Interface Studied by Surface-Enhanced Infrared Absorption Spectroscopy

Abstract: The structure and orientation of water molecules at a highly ordered Au(111) electrode surface in perchloric acid have been investigated in-situ as a function of applied potential by means of surface-enhanced infrared absorption spectroscopy. This newly developed infrared spectroscopy technique enables the observation of the electrode/electrolyte interface at a very high sensitivity without interference from the bulk solution. The spectrum of the interfacial water significantly differs from that of bulk water and drastically changes in peak frequencies and band widths around the potential of zero charge (pzc) of the electrode and at about 0.3 V positive from the pzc. The interfacial water molecules are weakly hydrogen-bonded at potentials below the pzc and form a strongly hydrogen-bonded ice-like structure at potentials slightly above the pzc. The ice-like structure is broken at more positive potentials due to the specific adsorption of perchlorate ion, where one OH moiety of water is non-hydrogen-bonded ...

Infrared Spectroscopy of Three-Dimensional Self-Assembled Monolayers: N-Alkanethiolate Monolayers on Gold Cluster Compounds

Abstract: Transmission infrared spectroscopy has been used to probe the structure of alkanethiolate monolayers adsorbed onto nanometer-sized gold clusters. The alkyl chain lengths vary between propanethiolate and tetracosanethiolate; specifically the C3, C4, C5, C6, C7, C8, C10, C12, C16, C20, and C24 alkanethiolates have been examined as solid suspensions in KBr pellets. It has been found that the smaller chain lengths (C3, C4, and C5) are relatively disordered, with large amounts of gauche defects present, and thus most resemble the free alkanes in the liquid state. The longer length alkanethiolates are predominantly in the all trans zigzag conformation. There are detectable amounts of near surface gauche defects, the amount of which decreases with increasing chain length, and a reasonably high percentage of end-gauche defects, the relative amount of which increases with increasing chain length. Internal gauche defects cannot be detected. A model is proposed to explain these observations, and the data are compare...

Infrared spectroscopy of small size‐selected water clusters

Abstract: Infrared molecular beam depletion and fragment spectroscopy has been employed to study the absorption behavior of small water clusters [(H2O)n, n=2,3,4,5]. The spectral region between 3300 and 3800 cm−1 was covered with an injection‐seeded optical parametric oscillator. Size‐specific information has been obtained by dispersing the cluster beam with a secondary helium beam and measuring the depletion as a function of the scattering angle. Three absorption bands could be assigned to the water dimer (H2O)2, with the bonded OH stretch being localized at 3601 cm−1. For each of the larger water clusters (n=3,4,5), which have cyclic structures, two absorption bands could be identified, one belonging to the free OH stretch and the other being due to the excitation of the OH ring vibration. The measurements on free water clusters were complemented by studies on small water complexes formed on large argon clusters. The positions of the absorption bands observed in these spectra are close to those found for (H2O)n i...

FTIR Study of Carbon Monoxide Oxidation and Scrambling at Room Temperature over Gold Supported on ZnO and TiO2. 2

Abstract: An FTIR and quadrupole mass spectroscopic study of CO adsorption and oxidation with 16O2 and 18O2 on copper supported on ZnO and TiO2 is presented. The experimental results indicate that CO is adsorbed on the metallic particles dispersed on both oxides on two kinds of sites, on the normal terrace sites and on sites at the borderline of the particles. Moreover, on titania, a band at 2126 cm-1, assigned to CO adsorbed on isolated Cu atoms and/or on two-dimensional small clusters, is detected. A frequency shift of the bands of CO adsorbed on the metallic particles observed in the CO−O2 coadsorption experiments and the occurrence of a scrambling reaction between CO and 18O2 reveal that on all these samples, there are metallic sites which are able to adsorb at the same time oxygen atoms and carbon monoxide. Carbon dioxide and carbonate-like species are formed: the asymmetric stretching frequencies of CO2 and the quadrupole mass spectroscopic analysis reveal that with 18O2, different isotopic molecular CO2's a...

Biophysical techniques in photosynthesis

Abstract: Preface. Part One: Optical Methods. 1. Developments in Classical Optical Spectroscopy J. Amesz. 2. Linear and Circular Dichroism G. Garab. 3. Fluorescence K. Sauer, M. Debreczeny. 4. Ultrafast Spectroscopy of Photosynthetic Systems R. Jimenez, G.R. Fleming. 5. Data Analysis of Time-Resolved Measurements A.R. Holzwarth. 6. Photosynthetic Thermoluminescence as a Simple Probe of Photosystem II Electron Transport Y. Inoue. 7. Accumulated Photon Echo Measurements of Excited State Dynamics in Pigment-Protein Complexes T.J. Aartsma, R.J.W. Louwe, P. Schellenberg. 8. Spectral Hole Burning: Methods and Applications to Photosynthesis N. Raja, S. Reddy, G.J. Small. 9. Infrared and Fourier-Transform Infrared Spectroscopy W. Mantele. 10. Resonance Raman Studies in Photosynthesis - Chlorophyll and Carotenoid Molecules B. Robert. 11. Stark Spectroscopy of Photosynthetic Systems S.G. Boxer. 12. The Photoacoustic Method in Photosynthesis - Monitoring and Analysis of Phenomena which Lead to Pressure Changes Following Light Excitation S. Malkin. Part Two: Magnetic Resonance. 13. Magnetic Resonance: an Introduction A.J. Hoff. 14. Time-Resolved Electron Paramagnetic Resonance Spectroscopy - Principles and Applications H. Levanon. 15. Electron Spin Echo Methods in Photosynthesis Research R.D. Britt. 16. ENDOR Spectroscopy W. Lubitz, F. Lendzian. 17. Optically Detected Magnetic Resonance (ODMR) of Triplet States in Photosynthesis A.J. Hoff. 18. MagicAngle Spinning Nuclear Magnetic Resonance of Photosynthetic Components H.J.M. de Groot. Part Three: Structure and Oxygen. 19. Structure Determination of Proteins by X-Ray Diffraction M. Schiffer. 20. Electron Microscopy E.J. Boekema, M. Roegner. 21. X-Ray Absorption Spectroscopy:Determination of Transition Metal Site Structures in Photosynthesis V.K. Yachandra, M.P. Klein. 22. Moessbauer Spectroscopy P.G. Debrunner. 23. Characterization of Photosynthetic Supramolecular Assemblies Using Small Angle Neutron Scattering D.M. Tiede, P. Thiyagarajan. 24. Measurements of Photosynthetic Oxygen Evolution H.J. van Gorkom, P. Gast.

Hydrogen in amorphous and microcrystalline silicon films prepared by hydrogen dilution

Abstract: Hydrogen incorporation in silicon layers prepared by plasma‐enhanced chemical‐vapor deposition using silane dilution by hydrogen has been studied by infrared spectroscopy (IR) and elastic recoil detection analysis (ERDA). The large range of silane dilution investigated can be divided into an amorphous and a microcrystalline zone. These two zones are separated by a narrow transition zone at a dilution level of 7.5%; here, the structure of the material cannot be clearly identified. The films in/near the amorphous/microcrystalline transition zone show a considerably enhanced hydrogen incorporation. Moreover, comparison of IR and ERDA and film stress measurements suggests that these layers contain a substantial amount of molecular hydrogen probably trapped in microvoids. In this particular case the determination of the total H content by IR spectroscopy leads to substantial errors. At silane concentrations below 6%, the hydrogen content decreases sharply and the material becomes progressively microcrystalline...

Size‐selected vibrational spectra of phenol‐(H2O)n (n=1–4) clusters observed by IR–UV double resonance and stimulated Raman‐UV double resonance spectroscopies

Abstract: OH and CH stretching vibrations of bare phenol, phenol‐(H2O)n clusters (n=1–4), and partially deuterated clusters in the S0 state were observed by using IR–UV double resonance and stimulated Raman‐UV double resonance spectroscopies. Characteristic spectral features of the OH stretching vibrations of the phenol as well as of the H2O sites were observed, which are directly related to their structures. The cluster structures were investigated by comparing the observed spectra with the calculated ones obtained by the ab initio molecular orbital calculation with (self‐consistent field) SCF 6‐31G and SCF 6‐31G* basis sets given by Watanabe and Iwata. It was found that for the clusters with n≥2, the isomer of ring form hydrogen‐bonded structure is most stable and the simulated IR spectra based on the calculated structure showed good agreements with the observed ones. For a particular cluster, which was assigned as an isomer of the n=4 cluster, an anomalous IR spectrum was observed. Two forms of the isomer are proposed with respect to the structure of water moiety: (1) an ‘‘ice’’ structure and (2) an ‘‘ion‐pair’’ structure. The relative IR absorption cross sections of each bands were also investigated for the clusters with n=1 to 4. It was found that the IR absorption cross section of the phenolic OH stretching vibration of the n=1 cluster increases by a factor of 6 compared to that of bare phenol and it further increases with the cluster size.

Structure of alumina surfaces

Abstract: The structure of hydroxylated alumina surface is analysed by IR spectroscopy The variety of OH groups differing in number and coordination of surrounding metal atoms, for the completely hydrated surface, either formed by ideal low-index planes, or complicated by crystal edges and corners or cation vacancies, is restricted to six, but grows dramatically upon dehydroxylation The results account for the complex structure observed previously in the IR spectra of surface OH groups after high-temperature treatment, and enable us to explain specific properties of transition aluminas

Investigations at the air/water interface using polarization modulation IR spectroscopy

Abstract: The ability of polarization modulation IR reflection absorption spectroscopy (PM–IRRAS) to study the air/water interface is presented. A brief description of the set-up and of the experimental procedure is given. Theoretical simulations accounting for the uniaxial nature of the spread monolayer lead to optimum experimental conditions (71 ° for the angle of incidence) and to a specific surface selection rule. Application to the study of cadmium arachidate, dimyristolyl phosphatidylcholine (DMPC) and polypeptidic Langmuir films illustrates the potential uses of this method.

Polymer-clay nanocomposites: Free-radical grafting of polystyrene on to organophilic montmorillonite interlayers

Abstract: Vinyl monomer-montmorillonite intercalates, which are able to swell and disperse in organic solvents, have been prepared by a cation exchange process by the interaction between the Na+ or Ca2+ cations of montmorillonite and vinylbenzyltrimethylammonium chloride. The resulting vinyl monomer-montmorillonite materials have been identified by X-ray diffraction (XRD), elemental analysis and infrared absorption spectra. Free-radical solution polymerizations of the penetrated styrene between the interlayers of 5, 10, 25 and 50 wt% vinyl monomer-montmorillonite have resulted in grafted polystyrenemontmorillonite materials. The effect of montmorillonite amounts on the formed polystyrene was determined by extraction with organic solvents, which showed an increase in the grafted polymer formed (0.84–2.94 g/g MMT), and a decrease in the external polystyrene with increasing amounts of montmorillonite. The molecular weight of the external polystyrenes was found to be in the range of 22000. The vinyl monomer-montmorillonite and polymer-montmorillonite intercalates have been identified by XRD, elemental analysis and infrared spectroscopy. Examination of the polystyrene-montmorillonite materials by SEM, TEM and XRD showed spherical particles of nanosize about 150–400 nm, and basal spacings of 1.72–2.45 nm.

Titanosilicate Mesoporous Molecular Sieve MCM-41: Synthesis and Characterization

Abstract: The location and coordination of titanium in the titanosilicate mesoporous molecular sieve MCM-41 prepared from Ti(IV) ethoxide as the source of titanium was studied by XRD, IR spectroscopy, 29Si MAS NMR, and XANES. The results are interpreted on the basis of isomorphous substitution of Ti for Si. XANES shows that titanium is 4-coordinate and that Ti(IV) does not form a regular TiO4 tetrahedron. This is caused by the larger size of the Ti(IV) atom in comparison with Si(IV), resulting in a distortion in the silica matrix, and/or by the presence of H2O in the coordination sphere of titanium. Such distortion is consistent with the line broadening observed in the 29Si MAS NMR spectra, brought about by the wider distribution of the Si−O−Si angles in SiO4 tetrahedra as titanium is progressively incorporated in the silica matrix, and with the changes in the vibrational lattice infrared bands.

On the Nature of Water Bound to a Solid Acid Catalyst

Abstract: The nature of the species formed when water interacts with Bronsted acid sites in a microporous solid acid catalyst, HSAPO-34, was studied by powder neutron diffraction and infrared spectroscopy. Previous infrared and computational studies had failed to unambiguously establish whether water is protonated to form hydronium (H3O+) ions or is merely hydrogen-bonded to acid sites inside the zeolite. Our experiments clearly showed that both species are present: An H3O+ ion is found in the eight-ring channel of the zeolite and a second water molecule is hydrogen-bonded to an acid site on the six-ring.

Structural investigations of phosphate glasses: a detailed infrared study of the x(PbO)-(1−x) P2O5 vitreous system

Abstract: The results and detailed discussion of an extensive experimental study of infrared spectra of the x (PbO)-(1−x)P2O5 vitreous system (x=0.3–0.75) together with a brief review of infrared spectra of phosphate compounds, are presented. Theoretical models employed in the interpretation of infrared spectra of glasses have been reviewed. The frequency ranges of various infrared bands belonging to PO 4 3− and P2O 7 4− , observed in different phosphate compounds, are discussed. The glassy and quenched samples were prepared from PbO and NH4H2PO4 by the rapid quenching technique. The infrared spectra of the constituents of the system, PbO and P2O5, in their polycrystalline and glassy forms, have been discussed. The intensity and wavenumbers of the infrared bands around 1600 and 3300 cm−1, assigned to the bending and stretching modes in H2O trapped by the hygroscopic glasses, have been followed for different compositions with x<0.5. The changes observed in these infrared bands established the role of water as an additional glass modifier. The intensity and frequency variations of the infrared bands have been followed through all the compositions for characteristic phosphate group frequencies including P=O, P-O-P stretching and bending modes and P-O bending mode. The results clearly suggest that the x(PbO)-(1−x)P2O5 system undergoes gradual structural changes from metaphosphate (x=0.5), to pyrophosphate (x=0.66) and to orthophosphate (x=0.75). The continuing presence of the infrared band, in varying intensity, in the region 1200–1280 cm−1 attributed to P=O, suggests that the glass-forming ability of the binary system is extendable at least up to x=0.66 composition, and that no complete rupture of P=O bond by Pb2+ takes place. The ionic character of the phosphate groups, P-O(−), PO 4 3− is well revealed by significant changes with the PbO content in the spectral features of the infrared bands around 1120 and 980 cm−1 respectively. The maximum intensity of the P-O(−) band at 1120 cm−1 for 55 mol% PbO suggests a partial breakdown of the covalent vitreous network of the phosphates and formation of a crystalline phase consisting of ionic groups PO 4 3− , P2O 6 2− and P2O 7 4− for PbO greater than 55 mol%. The observed pattern of variation in the intensity of the infrared bands in the 940–1080 cm−1 region attributed to the v3-mode in PO 4 3− , suggests a gradual transformation of PO 4 3− units to PO 3 − groups in lead meta-phosphate glass and then their restoration to PO 4 3− groups of pyro- and ortho-phosphate quenched samples. The results indicate a gradual decrease in the number of bridging oxygens and increase in the resonance behaviour of non-bridging oxygens as the mole percentage of metal oxide (PbO) increases in the glass. The infrared spectra of several binary phosphate glasses have been reviewed in the context of the study of effect of the cation on the infrared spectra. It is found that the influence of the cation on the infrared spectra of phosphate glasses does not show any striking regularity. Theoretical calculations of these band frequencies were found to agree well only in the case of pure stretching (P=O and O-H) vibrations and pure bending (P-O-P and O-H) vibrations. The disagreement in the case of P-O(−), P-O-H and other modes of P-O-P groups, has been attributed to the mixed nature of modes occurring in glasses. The changes in the positions of the characteristic bands and their relative intensities are strongly dependent on the structural units and PbO content in the phosphate glasses and the results emphasize the role of PbO as a network modifier.

Surface Modification of Small Particle TiO2 Colloids with Cysteine for Enhanced Photochemical Reduction: An EPR Study†

Abstract: Surface complexation of colloidal titanium dioxide nanoparticles (40−60 A) with cysteine was investigated by electron paramagnetic resonance (EPR) and infrared (diffuse reflectance infrared Fourier transform−DRIFT) spectroscopies Cysteine was found to bind strongly to the TiO2 surface, resulting in formation of new trapping sites where photogenerated electrons and holes are localized Illumination of cysteine-modified TiO2 at 77 K resulted in formation of cysteine radicals with the unpaired electron localized on the carboxyl group Upon warming to 150 K, these radicals are transformed into sulfur-centered radicals as observed by EPR spectroscopy We have demonstrated the existence of two surface Ti(III) centers on cysteine-modified TiO2 particles having different extents of tetragonal distortion of the octahedral crystal field Upon addition of lead ions, a new complex of cysteine that bridges surface titanium atoms and lead ions was detected by IR spectroscopy Illumination of lead/cysteine-modified TiO

Interaction of Pyridine with Acidic (H-ZSM5, H-β, H-MORD Zeolites) and Superacidic (H-Nafion Membrane) Systems: An IR Investigation

Abstract: The interaction of pyridine with acidic H-ZSM5, H-β, and H-MORD zeolites and a perfluorosulfonic superacidic membrane (H-Nafion) has allowed us to study the IR spectrum of PyH+ hydrogen bonded to the negative zeolite skeleton (Z-) or to CF2SO3- groups of the membrane. In the presence of excess Py the formation of PyH+···Py is also detected. On H-MORD (a zeolite with higher Al content) the adsorption of Py at room temperature is limited to the external surfaces of the crystallite, owing to the blockage of channel mouths caused by the PyH+ formed in high concentration. The IR spectra of hydrogen-bonded PyH+ in the ν(NH···) stretching region are strongly influenced by Fermi resonance effects with the overtones and combinations of low-frequency modes. In the H-Nafion/Py system the modification induced by the proton transfer on the internal modes of the −SO3H groups (with formation of SO3- species) gives additional information on the proton transfer process. To complete the assignment of all the observed surfa...

Vibrational spectra and structure of heavy metal oxide glasses

Abstract: The infrared reflectance spectra at near-normal and off-normal incidence and polarized Raman spectra have been investigated to characterize the structure of PbOBi2O3Ga2O3 glasses. Infrared reflectance bands at 400 cm−1, 470 cm−1 and 610 cm−1 have been assigned to PbO, BiO and GaO related vibrations, respectively. The polarized Raman spectra were deconvoluted into seven bands which have been classified into four sets of modes: (1) depolarized low-frequency Raman modes at 30–70 cm−1, (2) strongly polarized Pb and Bi heavy metal vibrations at 120 to 140 cm−1: (3) polarized GaOPb, GaOBi, BiOPb, GaOGa and BiOBi bridging-oxygen modes at 300–600 cm−1; (4) non-bridging-oxygen modes at 600–700 cm−1. The optic vibrations observed in the series of glasses indicate that most cations behave essentially as network-formers. The low-frequency Raman scattering was analyzed on the basis of Martin and Brenig's acoustic model, from which some intermediate range structural information is derived. The structural correlation and structural units which determine the high frequency modes in these glasses are discussed.

The origin of photoluminescence from thin films of silicon-rich silica

Abstract: We have carried out a study of the photoluminescence properties of silicon‐rich silica. A series of films grown using plasma enhanced chemical vapor deposition over a range of growth conditions were annealed under argon at selected temperatures. Photoluminescence spectra were measured for each film at room temperature and for selected films at cryogenic temperatures. The photoluminescence spectra exhibit two bands. Fourier transform infrared and electron spin resonance spectroscopies were used to investigate bonding and defect states within the films. The data obtained strongly suggest the presence of two luminescence mechanisms which exhibit different dependencies on film growth conditions and postprocessing. We make assignments of the two mechanisms as (1) defect luminescence associated with oxygen vacancies and (2) radiative recombination of electron‐hole pairs confined within nanometer‐size silicon clusters (‘‘quantum confinement’’).

Investigation of Surfactant Conformation and Order at the Liquid−Liquid Interface by Total Internal Reflection Sum-Frequency Vibrational Spectroscopy

Abstract: The conformational order of sodium dodecyl sulfate (SDS) adsorbed at the D2O-CCl4 interface has been examined by total internal reflection sum-frequency vibrational spectroscopy. A change in conformation of the alkyl chain with increased surface coverage at the liquid−liquid interface is observed. A series of aqueous surfactant concentrations have been examined in order to determine the effect of surface coverage on the conformation of the alkyl chains at the interface. Polarization studies indicate that, for the concentration range examined, the symmetry axis of the terminal methyl group on the alkyl chain is oriented primarily along the surface normal. Identification of spectral features in the C−H region of the infrared region is facilitated by examination of the sum-frequency spectrum from an analogous deuterated compound.

Catalytic Cleavage of the C-H and C-C Bonds of Alkanes by Surface Organometallic Chemistry: An EXAFS and IR Characterization of a Zr-H Catalyst

Abstract: The catalytic cleavage under hydrogen of the C & singlebond;H and C & singlebond;C bonds of alkanes with conventional catalysts requires high temperatures Room-temperature hydrogenolysis of simple alkanes is possible on a well-defined and well-characterized zirconium hydride supported on silica obtained by surface organometallic chemistry The surface structure resulting from hydrogenolysis of (≡SiO)Zr(Np)3 (Np, neopentyl) was determined from the extended x-ray absorption fine structure (EXAFS) and 1H and 29Si solid-state nuclear magnetic resonance and infrared (IR) spectra A mechanism for the formation of (≡SiO)3Zr-H and (≡SiO)2SiH2 and the resulting low-temperature hydrogenolysis of alkanes is proposed The mechanism may have implications for the catalytic formation of methane, ethane, and lower alkanes in natural gas