12597-02-3Relevant articles and documents
Reaction of S2 with ZnO and Cu/ZnO surfaces: Photoemission and molecular orbital studies
Chaturvedi, Sanjay,Rodriguez, Jose A.,Hrbek, Jan
, p. 10860 - 10869 (1997)
The adsorption of S2 on ZnO and Cu/ZnO has been investigated using synchrotron-based high-resolution photoemission spectroscopy. On dosing a clean ZnO surface with S2 at 300 K, the molecule dissociates. The S is associated first with Zn and at medium coverages with Zn-O sites. When the sulfur coverage is increased to θs = 0.5 ML, evidence is found for sulfur bound purely to the O sites of ZnO. The sulfur species associated with O and the Zn-O sites are unstable at temperatures above 500 K. Possible reaction pathways for the dissociation of S2 on ZnO(0001)-Zn and Zn(1010) surfaces were studied using ab initio SCF calculations. At low sulfur coverages, an adsorption complex in which S2 is bridge bonded to two adjacent Zn atoms (Zn-S-S-Zn) is probably the precursor state for the dissociation for the molecule. It is possible to get much higher coverages of sulfur on ZnO (0.7 ML) than on Al2O3 (0.1 ML) at similar S2 exposures. This, in conjunction with results previously reported for H2S adsorption on Cr2O3 and Cr3O4, indicates that the reactivity of metal oxides toward sulfur is inversely proportional to the size of their band gap. Oxides with a large band gap (e.g., Al2O3, ～9.0 eV) are less susceptible to sulfur adsorption than oxides with a small band gap (e.g., ZnO, ～3.4 eV). The presence of Cu atoms on both metal oxides enhances their respective reactivities toward S2. Upon dosing Cu/ZnO with S2 at 300 K, sulfur prefers to attack supported Cu followed by reaction with the Zn sites of the oxide, and at large sulfur coverages the adsorbate bonds simultaneously to metal and oxygen sites on the surface. The sulfur bonded to both the metal and oxygen sites on the surface is relatively weakly bound and desorbs by 500 K. The Cu ?? S interactions are strong and lead to the formation of copper sulfides that exhibit a distinctive band structure and decompose at temperatures above 700 K.
S2 (a 1Δ ) production in the photolysis of reduced sulfides: Production chemistry, spectroscopy and interference potential in the LIF detection of OH
Hynes,Richter,Rosendahl,Clark
, p. 25 - 33 (1998)
Production of S2 (a 1Δ, v=2) has been observed in the UV photolysis of several reduced sulfur compounds by monitoring the f 1Δ-a 1Δ (2-3) laser excitation spectrum. There appears to be at least three production mechanisms including reaction of S (1D) with the precursor. The f-a (2-3) band shows several spectral overlaps with the OH A 2Σ-X 2Π (1-0) band including the Q11 line. Since a significant fraction of the f-a emission from f 1Δ (v=2) overlaps the OH A-X (1-1) and (0-0) bands the potential for a significant 'interference' signal exists if the two species are produced simultaneously.
The adsorption of sulfur on Rh(111) and Cu/Rh(111) surfaces
Rodriguez, Jose A.,Chaturvedi, Sanjay,Kuehn, Mark
, p. 3064 - 3073 (1998)
The reaction of S2 with Rh(111) and Cu/Rh(111) surfaces has been investigated using synchrotron-based high-resolution photoemission, thermal desorption mass spectroscopy and ab initio self-consistent-field calculations. At 100 K, the adsorption of S2 on Rh(111) produces multilayers of Sn species (n = 2-8) that desorb between 300 and 400 K, leaving a film of RhSx on the sample. S2 dissociates upon adsorption on clean Rh(111) at 300 K. An adsorption complex in which S2 is bridge bonded to two adjacent Rh atoms (Rh-S-S-Rh) is probably the precursor state for the dissociation of the molecule. The larger the electron transfer from Rh(111) into the S2(2πg) orbitals, the bigger the adsorption energy of the molecule and the easier the cleavage of the S-S bond. On Rh(111) at 300 K, chemisorbed S is bonded to two dissimilar adsorption sites (hollow and probably bridge) that show well separated S 2p binding energies and different bonding interactions. Adsorption on bridge sites is observed only at S coverages above 0.5 ML, and precedes the formation of RhSx films. The bonding of S to Rh(111) induces a substantial decrease in the density of d states that the metal exhibits near the Fermi level, but the electronic perturbations are not as large as those found for S/Pt(111) and S/Pd(111). Cu adatoms significantly enhance the rate of sulfidation of Rh(111) through indirect Cu?Rh?S2 and direct Cu?S-S?Rh interactions. In the presence of Cu there is an increase in the thermal stability of sulfur on Rh(111). The adsorption of S2 on Cu/Rh(111) surfaces produces CuSy and RhSx species that exhibit a distinctive band structure and decompose at temperatures between 900 and 1100 K: CuSy/RhSx/Rh(111)→S2(gas) + Cu(gas) + S/Rh(111).
State-resolved photodissociation of OCS monomers and clusters
Sivakumar, N.,Hall, G. E.,Houston, P. L.,Hepburn, J. W.,Burak, I.
, p. 3692 - 3708 (1988)
Photodissociation of OCS in the region from 222-248 nm has been investigated by monitoring the CO and S(1D2) primary photoproducts; as well as the secondary production of S(3P2), S(3P1), and S(3P0) using fluorescence induced by a tunable vacuum ultraviolet laser source based on four-wave mixing in magnesium vapor.The quantum yield of S(3P) was found to be 0.00 +/- 0.02 at 222 nm.Thus, in contrast to our preliminary report, the present more detailed investigation shows that the sole sulfur product appears to be S(1D).The CO photofragment is produced almost exclusively in ν = O 0.02>, but the rotational distribution is inverted and peaked at very high rotational levels.The peak shifts from J = 56 for dissociation at 222 nm to J = 31 at 248 nm.Doppler profiles of the CO rotational transitions reveal ( I ) that all observed levels are produced in coincidence with S (1D), (2) that for 222 nm photolysis the fragment recoil anisotropy shifts from a distribution characterized by β = 1.9 at J = 67 toward one characterized by β = O near J = 54, ( 3 ) that the CO velocity vector is aligned nearly perpendicular to its angular momentum vector, and (4) that the CO angular momentum vector is also aligned parallel to that component of the transition dipole which lies perpendicular to the recoil velocity.These results are interpreted in terms of a model for the dissociation in which excitation takes place to two surfaces of A ' and A N symmetry derived from a bent 1D configuration.Dissociation of OCS clusters was also investigated and was found to produce a photochemistry completely different from that of the monomers.Rotationally cold CO as well as S2 in both the X 3Σ-g and a1 δsg states was observed.
Formation of Mo and MoSx nanoparticles on Au(1 1 1) from Mo(CO)6 and S2 precursors: Electronic and chemical properties
Rodriguez, José A.,Dvorak, Joseph,Jirsak, Tomas,Hrbek, Jan
, p. 315 - 326 (2001)
Mo(CO)6 can be useful as a precursor for the preparation of Mo and MoSx nanoparticles on a Au(1 1 1) substrate. On this surface the carbonyl adsorbs intact at 100 K and desorbs at temperatures lower than 300 K. Under these conditions, the dissociation of the Mo(CO)6 molecule is negligible and a desorption channel clearly dominates. An efficient dissociation channel was found after dosing Mo(CO)6 at high temperatures (400 K). The decomposition of Mo(CO)6 yields the small coverages of pure Mo that are necessary for the formation of Mo nanoclusters on the Au(1 1 1) substrate. At large coverages of Mo (0.15 ML), the dissociation of Mo(CO)6 produces also C and O adatoms. Mo nanoclusters bonded to Au(1 1 1) exhibit a surprising low reactivity towards CO. Mo/Au(1 1 1) surfaces with Mo coverages below 0.1 ML adsorb the CO molecule weakly (desorption temperaturex nanoparticles. The formed MoSx species are more reactive towards thiophene than extended MoS2(0002) surfaces, MoSx films or MoSx/Al2O3 catalysts. This could be a consequence of special adsorption sites and/or distinctive electronic properties that favor bonding interactions with sulfur-containing molecules.
A deperturbation analysis of the B3∑u- =(v′ = 0-6) and the B″ 3∏u(v′ = 2-12) states of S2
Green,Western
, p. 848 - 864 (1996)
Laser-induced fluorescence spectra of 32S2 have been obtained, covering v′=0-6 of the B 3-∑u- X 3∑g- transition and v′=2-12 of the B″ 3∏u-X 3∑g- transition, using static cell and supersonic free jet techniques. The spectra include transitions to the previously unseen B″ 3∏2,u components. Analysis of the many perturbations between the two upper electronic states has been carried out using a Hamiltonian matrix including all the B and B″ states simultaneously rather than deperturbing individual pairs of vibronic states. This takes into account longer range interactions and gives deperturbed molecular constants that vary smoothly with vibrational state. Our model for the B″ v′ = 2-12 and B v′=0-6 levels covering J up to 100 can fit all 3320 observed transitions with an average error of 0.064 cm-1. The widely ranging fluorescence lifetimes of the B″ state vibronic levels provide independent information about the state mixing and confirm the model, since the observed B″-X fluorescence arises almost entirely via this mixing. However, lifetime measurements of the newly observed Ω=2 components of the B″ state showed little variation in lifetimes, about an average of 4.2±0.4 μs. This indicates a small intrinsic B″-X transition strength as the Ω=2 components are essentially not mixed with the B state. A model for the perturbation parameters is developed, based on Franck-Condon factors between the two states. The magnitude of the perturbations and transition moments are discussed in relation to the electronic configurations of the B and B″ states. 1996 American Institute of Physics.
Adsorption of sulfur on Ag/Al2O3 and Zn/Al2O3 surfaces: Thermal desorption, photoemission, and molecular orbital studies
Rodriguez, José A.,Kuhn, Mark
, p. 3187 - 3195 (1997)
The interaction of S2 with Ag/Al2O3 and Zn/Al2O3 surfaces has been investigated using thermal desorption mass spectroscopy, core- and valence-level photoemission, and ab initio self-consistent-field calculations. The sticking coefficient of S2 on clean alumina is small (2/Al2O3 system, there is an energy mismatch between the orbitals of the molecule and the bands of the oxide, and the reactivity of S2 on pure alumina is very low. The adsorption of sulfur on Ag/Al2O3 and Zn/Al2O3 surfaces induces strong perturbations in the electronic properties of the admetals and oxide support. In the Ag/Al2O3 and Zn/Al2O3 systems, the supported metal clusters (or particles) provide a large number of electronic states that are very efficient at donating charge into the S2(2πg) orbitals, inducing in this way the breaking of the S-S bond and the formation of admetal sulfides (AgSx and ZnSy). The larger the electron transfer from the supported metal into the S2(2πg) orbitals, the bigger the adsorption energy of the molecule and the easier the cleavage of the S-S bond. The AgSx and ZnSy species decompose at temperatures between 750 and 900 K following two different reaction pathways: AgSx,solid → S2,gas + Agsolid and ZnSy,solid → S2,gas + Zngas.
Reaction of H2S and S2 with metal/oxide surfaces: band-gap size and chemical reactivity
Rodriguez,Chaturvedi,Kuhn,Hrbek
, p. 5511 - 5519 (1998)
The adsorption and dissociation of H2S and S2 on a series of oxide (Al2O3, Cr2O3, Cr3O4, Cu2O, ZnO) and metal/oxide (Cu/Al2O3, Cu/ZnO) surfaces have been studied using synchrotron-based high-resolution photoemission. H2S and S2 mainly interact with the metal centers of the oxides. At 300 K, H2S undergoes complete decomposition. The rate of decomposition on Al2O3 is much lower than those found on Cr3O4, Cr2O3, ZnO, and Cu2O. For these systems, the smaller the band gap in the oxide, the bigger its reactivity toward S-containing molecules. The results of ab initio SCF calculations for the adsorption of H2S, HS, and S on clusters that resemble the (0001) face of α-Al2O3, α-Cr2O3, and ZnO show that the S-containing species interact stronger with Cr or Zn than with Al centers. These theoretical results and the trends seen in the experimental data indicate that the reactivity of an oxide mainly depends on how well its bands mix with the orbitals of H2S or HS. The electrostatic interactions between the dipole of H2S and the ionic field generated by the charges in the oxide play only a secondary role in the adsorption process. Photoemission results show that the rate of adsorption of H2S and S2 on Cu/Al2O3 and Cu/ZnO surfaces is much faster than on the pure oxides. A simple model based on perturbation theory and orbital mixing is able to explain the effects of the band-gap size on the reactivity of an oxide and the behavior of metal/oxide surfaces in the presence of S-containing molecules.
The bonding of sulfur to Pd surfaces: Photoemission and molecular-orbital studies
Rodriguez, Jose A.,Chaturvedi, Sanjay,Jirsak, Tomas
, p. 421 - 428 (1998)
The adsorption and dissociation of S2 on Pd(111) and polycrystalline Pd were studied using synchrotron-based high-resolution photoemission spectroscopy and ab initio SCF calculations. The photoemission results show several sulfur species with distinct electronic properties. The formation of Pd-S bonds induces large positive binding-energy shifts in the core and valence levels of Pd. After chemisorbing sulfur on the Pd surfaces, there is a substantial decrease in the electron density that the metal exhibits near the Fermi level and a simultaneous drop in the electron population of its 4d band. Pd is more sensitive to sulfur than other metals frequently used in automotive exhaust catalysts (Rh and Pt).
Study on sulfur vaporization from covellite (CuS) and anilite (Cu1.75S)
Brunetti, B.,Piacente, V.,Scardala, P.
, p. 113 - 120 (1994)
Covellite decomposes according to the reaction: 4.667CuS → 2. 667Cu1.75S(s) + S2(g). The sulfur vapour pressures measured in the temperature range 551.5-627 K by the torsion-effusion method are represented by the equation; log p (kPa
