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Bulk rutile TiO2and its (110) surface have been investigated with a computationally efficient semiempirical tight binding method: self-consistent-charge density functional tight binding (SCC-DFTB). Comparisons of energetic, mechanical, and electronic properties are made to density functional theory (DFT) and to experiment to characterize the accuracy of SCC-DFTB for bulk rutile TiO2and TiO2(110). Despite the fact that the SCC-DFTB parameters for Ti, Ti−Ti, and Ti−O were developed in the context of small biologically relevant Ti containing compounds, SCC-DFTB predicts many properties of bulk TiO2and the TiO2(110) surface with accuracy similar to local and gradient-corrected DFT. In particular, SCC-DFTB predicts a direct band gap of TiO2of 2.46 eV, which is in better agreement with experiment, 3.06 eV, than DFT utilizing the local density approximation (LDA), 2.0 eV. SCC-DFTB also performs similar in terms of accuracy as LDA-DFT for the phonon frequencies of the bulk lattice and for the relaxed geometry of the TiO2(110) surface. SCC-DFTB does, however, overestimate the surface energy of TiO2(110) compared to LDA-DFT. Nevertheless, the overall accuracy of SCC-DFTB, which is substantially more computationally efficient than DFT, is encouraging for bulk rutile TiO2and TiO2(110).

The kinetics of elementary reactions involved in the chain chlorination of cyclopropane are examined using a combination of absolute and relative rate constant measurements and first principles electronic structure calculations. Relative rate methods are used in a smog chamber FTIR apparatus to determine k(Cl + c-C3H6) = (1.15 ± 0.17) × 10^-13 and k(Cl + c-C3H5Cl) = (1.06 ± 0.18) × 10^-12 cm³ molecule^-1 s^-1 in 10−700 Torr of air, or N2, diluent at 296 K. Absolute rate coefficients for the reaction of Cl with cyclopropane are measured between 293 and 623 K by a laser-photolysis/CW infrared absorption method. The data can be represented in Arrhenius form as k(Cl + c-C3H6) = ((1.8 ± 0.3) × 10^-10 cm³ molecule^-1 s^-1)e^{-(2150±100)/T}. To support the experimental investigations, first principles electronic structure calculations are performed. Vibrational spectra of c-C3H5Cl, c-C3H4Cl2, and c-C3H3Cl3 are calculated and are presented. gem-C3H4Cl2 is calculated to be the kinetically and thermodynamically most favored dichlorocyclopropane. The experimental observations are consistent with the computational findings.

The synthesis, IR spectrum, and first-principles characterization of CF3CH(ONO)CF3 as well as its use as an OH radical source in kinetic and mechanistic studies are reported. CF3CH(ONO)CF3 exists in two conformers corresponding to rotation about the RCO&bond;NO bond. The more prevalent trans conformer accounts for the prominent IR absorption features at frequencies (cm⁻¹) of 1766 (N&dbond;O stretch), 1302, 1210, and 1119 (C&bond;F stretches), and 761 (O&bond;N&bond;O bend); the cis conformer contributes a number of distinct weaker features. CF3CH(ONO)CF3 was readily photolyzed using fluorescent blacklamps to generate CF3C(O)CF3 and, by implication, OH radicals in 100% yield. CF3CH(ONO)CF3 photolysis is a convenient source of OH radicals in the studies of the yields of CO, CO2, HCHO, and HC(O)OH products which can be difficult to measure using more conventional OH radical sources (e.g., CH3ONO photolysis). CF3CH(ONO)CF3 photolysis was used to measure k(OH + C2H4)/k(OH + C3H6) = 0.29 ± 0.01 and to establish upper limits of 16 and 6% for the molar yields of CO and HC(O)OH from the reaction of OH radicals with benzene in 700 Torr of air at 296 K. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 159–165, 2003

Alkaline earth oxides are leading candidates as NOx (x = 1, 2) sorbents; however, the understanding of adsorption and reaction of NOx on these surfaces is currently limited. In this paper, Mg(001) terrace cluster models and density functional theory (DFT) are used to characterize the adsorption properties of neutral and charged NO, NO2, and NO3. Neutral NO and NO2 molecules weakly adsorb on the MgO terrace, while neutral NO3 adsorbs more strongly through oxidation and significant acid−base coordination with the surface. Chemisorbed nitrite can be formed either from adsorption of Lewis acidic NO⁺ on Lewis base surface sites (Os^2-) or from adsorption of Lewis basic NO2^- on Lewis acid surface sites (Mgs²⁺). Similarly, chemisorbed nitrate can form from NO2⁺ adsorption on Os^2- sites or NO3^- adsorption on Mgs²⁺ sites. These charged adsorbates are not expected to exist in isolation on the MgO surface but rather are expected to form oppositely charged, cooperatively bound pairs with enhanced adsorption energy over the isolated neutrals. While results are demonstrated for adsorption on MgO, they have application to NOx adsorption on a wide range of oxide surfaces.

An extensive search for stable chemisorbed SO2 configurations on the Pt(111) surface has been performed using first-principles DFT−GGA calculations. The most energetically stable configurations, η²-Sb,Oa and η³-Sa,Oa,Oa at fcc sites, where η² and η³ mean that the number of atoms of the adsorbate coordinated to surface atoms are two and three, respectively, and the subscripts a and b stand for the atoms on atop sites and bridge sites, respectively, are consistent with experimental observations. It is found that strong sulfur−metal bonds are essential in stabilizing the molecular SO2 binding to the Pt(111) surface. The lateral dipole−dipole interactions among chemisorbed SO2 moieties are shown to be responsible for the strong coverage effect of the SO2 binding energy to the surface. These strong lateral interactions do not greatly affect the molecular structures or relative binding energy differences among different binding configurations. The projected density of states and the induced density of states are studied in detail to explain binding effects.

The chemisorption of molecules on metal oxide surfaces is generally considered to occur by either an acid/base or a redox mechanism, with the former dominating on nonreducible and insulating oxides such as MgO. NO, NO2, and the less familiar NO3 are atypical adsorbates in that their most potent Lewis acidic and basic forms are generated by one-electron oxidation or reduction of the parent molecules. In this work, first-principles density functional theory supercell calculations are used to probe the adsorption chemistry of the nitrogen oxides on an undefected MgO(001) surface. The isolated adsorbates are found to physisorb (NO, NO2) or weakly chemisorb (NO3) to the MgO terrace. In contrast, adsorbate partners located on neighboring surface acid (Mgs) and base (Os) sites form strongly chemisorbed products with features characteristic of nitrite (NO2^-) and nitrate (NO3^-). The origin of this new class of “cooperative” chemisorption is shown to be electron transfer between two NOx species to generate Lewis acid (NOx⁺) and base (NOx^-) pairs that strongly chemisorb to the MgO surface and that are further stabilized by lateral electrostatic attraction. The relatively low ionization potentials and large electron affinities of the NOx molecules are key to enabling the cooperative effect on MgO. Even more pronounced cooperative effects are expected for NOx adsorption on more basic or acidic oxides, including those used for NOx remediation. The effect is also likely to have a role in the heterogeneous chemistry of other odd-electron adsorbates, including the halogen oxides and HOx radicals.

In order to evaluate the effect of size on the adsorption energies on small Pt particles, we have performed a series of DFT-GGA calculations on Pt clusters of varying sizes, between 3 and 25 atoms, and a Pt(111) slab, with and without O and S adsorbates. We have found a significant variation in the energy of adsorption as a function of cluster size. In particular, energies of adsorption on the Pt10 cluster showed the largest deviation from those on the slab surface. Structural and energetic properties compare excellently to published experimental data. The Pt4 clusters with and without adsorbates were found to have reduced symmetry due to the Jahn−Teller effect. A simple rule between the cohesive energy and the size of small close-packed platinum particles is derived and confirmed by our first-principle calculations, the extrapolation of which excellently matches both experimental and computational bulk cohesive energies.

One of the main obstacles to the use of alkaline-earth-oxide-based NOx adsorbents for emissions control is the ready poisoning of these materials by SOx. To shed light on the mechanisms of poisoning, density functional theory (DFT) calculations and infrared spectroscopy experiments are used to study SOx adsorption on MgO as a model alkaline earth oxide. DFT plane-wave, pseudopotential results are presented for SOx adsorption on MgO(001) terraces and steps. Both SO2 and SO3 are found to exhibit both weakly bound physisorbed and strongly bound chemisorbed forms, with minimal activation barriers separating the two. Chemisorption is dominated by interactions between Lewis acidic sulfur and Lewis basic oxide anion sites to form surface sulfites and sulfates from SO2 and SO3, respectively. Within the generalized gradient approximation to DFT, the SO2 adsorption energy ranges from 25 kcal mol^-1 on terrace sites to 46 kcal mol^-1 on lower-coordinated step edge sites; analogous SO3 adsorption energies range from 49 to 76 kcal mol^-1. Surface sulfite is readily observed upon exposure of calcined MgO powder to SO2 and produces vibrational signatures consistent with that calculated for chemisorbed SO2. Sulfation is accomplished by exposure of the same powders to SO2 and O2 at elevated temperatures. Comparisons to calculated vibrational spectra indicate that both chemisorbed SO2 and SO3 are present under these conditions; further heating induces formation of a bulklike sulfate that is difficult to remove. The results demonstrate the high reactivity of SOx toward metal oxides and illustrate the challenges in developing sulfur-resistant oxide-based NOx traps.

We present a more detailed account of our recently reported [Hass, K. C.; Schneider, W. F.; Curioni, A.; Andreoni, W. Science 1998, 282, 265] first-principles molecular dynamics investigation of the static and dynamical behavior of adsorbed H2O on α-Al2O3 (0001). Al-terminated surfaces with varying degrees of H2O coverage are modeled using large periodic supercells. A predicted large relaxation of the clean surface agrees well with previous density functional theory calculations. Both molecular and dissociative H2O adsorption modes are identified, with the latter favored by ~10 kcal mol^-1. Complementary Al8O12 cluster results are shown to be unreliable because of their finite lateral extent. Constrained dynamical calculations of free-energy barriers indicate that the dissociation rate is very high, even in the absence of defects, but differs by 3 orders of magnitude for two equally exothermic pathways (proton transfer being more favorable across a six-membered ring than to the nearest O site). Unconstrained simulations at intermediate H2O coverages exhibit (1) spontaneous unimolecular and (2) H2O-mediated dissociation events, as well as (3) the diffusion and hydrogen bonding of physisorbed H2O and (4) an additional proton transfer reaction between adsorbed H2O and OH species. An experimentally observed decrease in H2O binding energies with coverage is explained in terms of a separation into defect-dominated, intrinsic (0001) terrace, and “hydrogen-bonding” regimes, with reasonable quantitative agreement throughout. Calculated O−H vibrational frequencies are consistent with known trends on aluminas but indicate a discrepancy between experimental observations for α-Al2O3 (0001) and models based on simple hydroxylation. Simulations for high H2O coverages suggest the possibility of more complicated behavior, including the interchange of adsorbed and lattice oxygen and the etching of surface Al. A “fully”-hydroxylated α-Al2O3 (0001) surface in which each surface Al is replaced by three protons to give uniform OH-termination, as in aluminum hydroxides, is the most likely result of prolonged exposure. Results for this surface confirm its anticipated stability, provide a reasonable explanation of observed vibrational spectra, and reveal a complex, dynamical structure with extensive intraplanar hydrogen bonding.

Effects of the support environment on the existence of Cu ion pairs in Cu-exchanged ZSM-5 catalysts are examined using density functional theory. Results for the molecular and electronic structures of O- and O2-bridged Cu oxocations ([CuOCu]²⁺ and [CuO2Cu]²⁺) are presented, including two distinct isomers for the latter. Both types of oxocations are predicted to be strongly bound for conditions likely to occur in the zeolite. The zeolite framework is represented by a variety of cluster models, including a previously established single-T-site model and larger multi-T-site models specific to particular binding sites in ZSM-5. With the largest models, bent Cu−Ox−Cu structures are found with Cu−Cu distances consistent with X-ray absorption data for Cu−ZSM-5. Implications for catalytic chemistry, including a proposed pathway for O2 formation and subsequent desorption from oxidized Cu sites in the zeolite, are discussed.

Explicit atom (EA) and united atom (UA) models are compared for the description of the structure and dynamics of an alkane film adsorbed on an Al-terminated α-Al2O3 (0001) surface. Ab initio calculations for an Al2O3···CH4 cluster are used to parameterize the EA model. One UA model is derived by explicit averaging of the EA potential, while the second is rescaled from the first to reproduce the EA octane adsorption energy. The appropriate scale factor is found to be sensitive to relaxation of the α-Al2O3 surface. The three models are compared in constant NVT molecular dynamics simulations of an octane monolayer (21 molecules) adsorbed on an 80% relaxed α-Al2O3 (0001) surface. Overall, the UA models reproduce the EA structural predictions well, the primary difference being an underestimation of the average gauche angle and overestimation of the trans fraction in the UA simulations. The agreement between dynamic predictions is less satisfactory; the scaled UA model reproduces the EA trans ↔ gauche interconversion rate reasonably well, but fails to reproduce the overall rotational or translational dynamics. UA models must be used with caution when applied to alkane dynamics on a corrugated surface.

A previously reported density-functional-theory-based model of NO decomposition in Cu-exchanged zeolites (Schneider, W. F.; et al. J. Phys. Chem. B 1997, 101, 4353) is extended to consider more generally the Cu-zeolite catalyzed chemistry of nitrogen oxides. The catalyst active site is considered to be an isolated, zeolite (Z)-bound Cu ion, which can exist in either a reduced (Z^-−Cu(I)) or an oxidized (Z^-−Cu(II)−O^-) state. Three different cluster models are used to study the affinity of ZCu and ZCuO for gaseous molecules (e.g., NO, NO2, or N2O), the structures and vibrational spectra of the stable complexes thus formed, and the possible reactivity between active sites and gaseous species. The reduced and oxidized states are found to react with nitrogen oxides via two types of O atom transfer reactions, one in which ZCu adds an O atom to form ZCuO, and the other in which ZCuO adds an O atom to form ZCu + O2 via a dioxygen (ZCuO2) intermediate. Potential energy surfaces for several key reactions are explored, and the results combined into a mechanistic model which can be used to rationalize much of the known catalytic chemistry of nitrogen oxides on Cu zeolites.

One-particle-inclusive measurements have been performed for the charge, kinetic energy and angular distributions of reaction products from238U +238U at 1 766MeV (7.42MeV/u) incident energy. The deep inelastic products exhibit features similar to those seen in reactions induced by medium heavy nuclei: increasing particle transfer is observed with increasing energy damping, the angular distributions are peaked near the grazing angle, they broaden significantly with increasing energy loss and/or charge transfer. The dominant reaction mechanism, however, is found to be sequential fission of one or both primary reaction products. The reconstructed primaryZ- andQ-value distributions show more particle transfer at a given energy loss than in other systems, i.e. the diffusion process seems to proceed colder in this system. This is confirmed by relatively large cross sections for surviving deep inelastic reaction products belowZ=92. A direct search fora-decay or fission of superheavy nuclei being produced in a deep inelastic reaction and being implanted in a surface barrier detector resulted in an upper cross section limit of 2 ×10-32cm2.

Angular distributions of the proton and neutron transfer reactions14C(16O,15N)15N and14C(16O,17O)13C leading to the ground states of the final nuclei were measured atElab=20, 25 and 30 MeV. A DWBA analysis was performed using the no-recoil approximation of Buttle and Goldfarb. All angular distributions, including the pronounced structures of the proton transfer arising from the fact that the final nuclei are identical, are well reproduced. The spectroscopic factor for the neutron transfer is in agreement with shell model calculations whereas the proton transfer into aj<-state yields a value which is too high. Exact finite-range calculations do not show this discrepancy, indicating that recoil effects are important even for light targets and lower energies. Contributions of the nonnormall-transfer, however, are small.

A small cluster model proposed earlier to examine bound Cu ions and their interaction with CO and NO in zeolites [Schneider, W. F.; Hass, K. C.; Ramprasad, R.; Adams, J. B. J. Phys. Chem. 1996, 100, 6032] is used to study Cu-bound dinitrosyl complexes. The possibility of a single-step, symmetric, concerted reaction occurring between the two nitrosyl ligands to form either a N−N bond or free N2 and O2 is addressed. Density functional theory is used to predict molecular and electronic structures and binding energies. N-down dinitrosyl binding to Cu⁰, Cu⁺, and Cu²⁺ can be represented as [Cu(I)−(NO)2^-], [Cu(I)−(NO)2], and [Cu(I)−(NO)2⁺], respectively, with the dinitrosyl moiety closely resembling the free NO dimer, and having a long N−N bond (≈2.8 Å). Dinitrosyl species bound to Cu through the O display two distinct binding modes, one resembling the N-down dinitrosyl binding, again with a long N−N bond (≈2.0 Å), and the other similar to hyponitrite binding to a metal atom, displaying a short N−N bond (≈1.2 Å). The single-step, symmetric, concerted decomposition reaction of NO in the vicinity of Cu ion sites in zeolites is forbidden by orbital symmetry and is anticipated to have a comparable or higher activation barrier than the same reaction in the gas phase. Metastable hyponitrite complexes, on the other hand, display N−N coupling and may be precursors for a multistep decomposition of NO in the presence of Cu-exchanged zeolites.

Protons and a-particles were measured in coincidence with fusion residues for the reaction48Ti+45Sc at 16 MeV/u beam energy. Their velocity distributions show a drastic broadening to higher as well as to lower velocities as compared to the calculated equilibrium emission pattern. This is interpreted as a kinematical effect of variations of the initial velocity of the emitting system, which are attributed to the preequilibrium emission of heavier clusters from the projectile or the target nucleus in incomplete fusion processes. The measured widths of the velocity distributions of the fusion residues are consistent with this mechanism. A peak in the product mass spectrum at masses between 6 and 18 is tentatively identified with the postulated cluster emission.

All reaction products in the range from target- and projectile-like to fission-like fragments were measured for the system84Kr+27Al at 5.9 MeV/u beam energy. They are assigned to the various reaction mechanisms on the basis of experimental signatures (energy dissipation, mass and angular distribution). The sum of the measured partial cross sections, including the evaporation residue yield obtained previously, agrees with the total reaction cross section derived from elastic scattering. A small fast-fission component was found, discernible from deep-inelastic reactions by its 1/sin ? angular distribution, and distinguished from compound-nucleus fission by an incomplete mass asymmetry relaxation.

Angular distributions for inelastic scattering, for 1 and 2-nucleon transfer reactions were studied at 18.2 MeV/u beam energy. Owing to sequential decay of excited reaction products the nuclide yield measured at various angles and in different regions of total kinetic energy loss (TKEL) does not represent the yield of primordial nuclidesAZ. Monte Carlo calculations were applied in order to reconstruct the primary double-differential cross-sections d2s/dOdTKEL for values of TKEL up to 80 MeV. By comparing the probability of inelastic scattering and that of transfer reactions it is found that the former dominates for TKEL< 10 MeV, whereas the situation is reversed above 20 MeV. No evidence is found for the excitation of giant resonances with significant cross section.

Evaporation residues from the heavy-ion fusion reaction50Ti on209Bi were investigated. They were separated from the projectile beam by the velocity filter SHIP and identified after implantation into an array of position-sensitive surface-barrier detectors by analyzing theira-decay chains. Spontaneous fission was also observed.

An experiment to synthesize element 109 is presented. Decay patterns characteristic of complete fusion products were searched for in an irradiation of209Bi targets with58Fe projectiles at specific incident energies of 4.95, 5.05, and 5.15 MeV/u. A total dose of 7 ×1017 particles was obtained. The experimental method involves in-flight separation of forward peaked reaction products with a static-field velocity filter, their passage through a time-of-flight device and their final implantation into position sensitive solid state detectors to measure their kinetic energy, approximate mass and their time and position of incidence. The subsequent decay of the narrowly localised reaction products by cascades of alpha particles and/or spontaneous fission is also registered in terms of the energies and times of all the emitted particles. One outstanding decay sequence that started with the emission of two alpha particles within subsequent time intervals of 5 ms and 22 ms and ended with spontaneous fission after 13 s was found at 5.15 MeV/u. The first alpha particle had a kinetic energy of (11.10±0.04) MeV. A detailed analysis of all the alternative interpretations of this observation, such as a purely random correlation of signals, the decay of a product from a transfer reaction or of any of the various energetically possible evaporation residues, shows that the isotope with mass 266 of element 109, i.e. the one neutron evaporation channel after complete fusion, is the statistically most significant assignment. The outlook for new element synthesis is also briefly discussed.

A search fora-decay of high spin isomers in the mass range 140132Xe and50Ti have been used to provide high velocity recoils with angular momenta beyond 50?. Recoil distance experiments sensitive to half lives longer than 10 ps and shorter than about 1 ns have been performed for 31 different compound nuclei. Within a sensitivity of 1–30µb per event no delayeda-emission has been observed.

Mass andZ-distributions of fusion products from the reaction 5.8 MeV/u46Ti+12C were measured in the angular range between?lab=1.5° and 8° using a time-of-flight?E-E telescope. The results are compared with an earlier measurement of the reaction32S+26Mg, in which the same compound nucleus was produced at higher excitation energy. The residual nuclide distributions are interpreted with the aid of evaporation calculations and the influence of shell effects in the level densities is discussed. The data are consistent with the assumption that the shell effects vanish above 15 to 20 MeV excitation energy, that is, that they are essentially only important for the last evaporation step.

We present data for the132Xe+56Fe-system at 5.73 MeV/u laboratory energy. Due to inverted kinematics, where Xe is the projectile, we were able to measure energy spectra as well as angular distributions for reaction products with 20?Z?60 with unitZ-resolution; i.e. target- and projectile-like fragments have been investigated. The reaction shows a well focussed quasielastic component, where charge transfer from the light to the heavy collision partner dominates. This apparent tendency towards more asymmetric fragmentation is explained by a potential energy surface which favours such charge transfer in order to minimize the asymmetry energy of the liquid drop. The strongly damped component which constitutes the major part of the reaction cross section exhibits characteristics of a fusion-fission reaction with typical fission fragment kinetic energies and 1/sinTc.m. angular distributions.

Pulse radiolysis and FT-IR smog chamber experiments were used to investigate the atmospheric fate of C6H5O(•) radicals. Pulse radiolysis experiments gave σ(C6H5O(•))235 nm = (3.82 ± 0.48) × 10^-17 cm² molecule^-1, k(C6H5O(•) + NO) = (1.88 ± 0.16) × 10^-12, and k(C6H5O(•) + NO2) = (2.08 ± 0.15) × 10^-12 cm³ molecule^-1 s^-1 at 296 K in 1000 mbar of SF6 diluent. No discernible reaction of C6H5O(•) radicals with O2 was observed in smog chamber experiments, and we derive an upper limit of k(C6H5O(•) + O2) &lt; 5 × 10^-21 cm³ molecule^-1 s^-1 at 296 K. These results imply that the atmospheric fate of phenoxy radicals in urban air masses is reaction with NOx. Density functional calculations and gas chromatography−mass spectrometry are used to identify 4-phenoxyphenol as the major product of the self-reaction of C6H5O(•) radicals. As part of this study, relative rate techniques were used to measure rate constants for reaction of Cl atoms with phenol [k(Cl + C6H5OH) = (1.93 ± 0.36) × 10^-10], several chlorophenols [k(Cl + 2-chlorophenol) = (7.32 ± 1.30) × 10^-12, k(Cl + 3-chlorophenol) = (1.56 ± 0.21) × 10^-10, and k(Cl + 4-chlorophenol) = (2.37 ± 0.30) × 10^-10], and benzoquinone [k(Cl + benzoquinone) = (1.94 ± 0.35) × 10^-10], all in units of cm³ molecule^-1 s^-1. A reaction between molecular chlorine and C6H5OH to produce 2- and 4-chlorophenol in yields of (28 ± 3)% and (75 ± 4)% was observed. This reaction is probably heterogeneous in nature, and an upper limit of k(Cl2 + C6H5OH) ≤ 1.9 × 10^-20 cm³ molecule^-1 s^-1 was established for the homogeneous component. These results are discussed with respect to the previous literature data and to the atmospheric chemistry of aromatic compounds.

First-principles quantum calculations are potentially of great value for assessing the plausibility of proposed catalytic reaction mechanisms. The present analysis of reaction pathways and energetics for key elementary steps in the catalytic decomposition of NO to N2 + O2 by Cu-exchanged zeolites yields novel insights into this widely studied reaction. We find evidence for a pathway involving two successive O-atom transfers to an isolated, zeolite-bound Cu⁺ center, initiated by formation of a short-lived and difficult to detect isonitrosyl intermediate, and yielding sequentially N2O and Cu-bound O followed by N2 and Cu-bound O2. The calculations allow us to identify a complete catalytic cycle with reasonable energetics.

Local spin density functional theory calculations of vibrational frequencies were performed for small Cu-containing complexes in an effort to assess models of exchanged Cu ion sites in zeolites and to help interpret infrared spectroscopy results. Model complexes consisted of Cuⁿ⁺ (n = 0−2) ions with varying coordination to water ligands and to more realistic fragments of zeolites. Calculated CO and NO vibrational frequencies for Cu-bound mono- and dicarbonyl and mono- and dinitrosyl species lie in ranges consistent with experimentally observed frequencies and confirm earlier assignments. Our results show a clear linear correlation between bond length and frequency for both carbonyl and nitrosyl complexes. The (nominal) oxidation state of Cu in these complexes is the most important factor in determining CO and NO frequencies and bond lengths, with the local coordination of Cu and the presence of explicit countercharges producing secondary effects.

Relative rate techniques were used to estimate k(OH+HFE-7100) ≈ 1.2 × 10^-14 cm³ molecule^-1 s^-1 at 295 K leading to an estimate of ≈5 years for the atmospheric lifetime of HFE-7100 (HFE = hydrofluoroether). Pulse radiolysis transient UV absorption spectroscopy was used to study the ultraviolet absorption spectra and kinetics of C4F9OCH2 and C4F9OCH2O2 radicals at 296 K. At 300 nm σ(C4F9OCH2) = (5.80 ± 0.76) × 10^-19 and at 250 nm σ(C4F9OCH2O2) = (2.24 ± 0.24) × 10^-18 cm² molecule^-1. Both UV spectra showed two absorption maxima, one below 230 nm and one at 290 nm. Rate constants for the self-reactions of C4F9OCH2 and C4F9OCH2O2 radicals, the reaction of C4F9OCH2 radicals with O2, and the reactions of C4F9OCH2O2 radicals with NO and NO2 were (3.5 ± 0.8) × 10^-11, (1.35 ± 0.17) × 10^-11 (uncorrected for possible secondary chemistry), (2.5 ± 0.5) × 10^-12, (8.5 ± 2.5) × 10^-12, and (8.8 ± 1.8) × 10^-12 cm³ molecule^-1 s^-1, respectively. Using a pulse radiolysis method we measured k(F+HFE-7100) = (1.6 ± 0.6) × 10^-11 cm³ molecule^-1 s^-1. Using a Fourier transform infrared spectroscopic technique rate, constants for the reaction of F and Cl atoms with HFE-7100 and Cl atoms with C4F9OC(O)H were determined to be (1.3 ± 0.3) × 10^-11, (9.7 ± 1.4) × 10^-14, and (1.6 ± 0.7) × 10^-14 cm³ molecule^-1 s^-1, respectively. Finally, it was determined that the sole atmospheric fate of C4F9OCH2O· radicals is reaction with O2 to give C4F9OC(O)H (perfluorobutyl formate). The results are discussed with respect to the atmospheric chemistry of HFE-7100.

Summary Recent progress in the modelling of exchanged Cu sites and their interactions with small molecules, based on DFT cluster calculations, is briefly reviewed.