CO Axis Research Articles

Influence of coadsorbed K on near-edge resonances for core and valence photoionization of CO on Ni(111).

With the use of synchrotron radiation, the resonant core and valence photoionization of CO adsorbed on Ni(111) has been measured for layers with and without coadsorbed K. Excitations from $\mathrm{C} 1s$ and $\mathrm{O} 1s$ levels into the bound-$\ensuremath{\pi}$ and $\ensuremath{\sigma}$ shape resonances, and from $4\ensuremath{\sigma}$ and $5\ensuremath{\sigma}$ into the latter, are compared. The energies of the $\ensuremath{\sigma}$ core resonances are markedly decreased by K coadsorption, indicating an increase of the C---O bond distance. The influence of K on the energies of the valence-coupled $\ensuremath{\sigma}$ shape resonance is small, and these energies are quite different from those for core ionization and among each other. This is understandable qualitatively in terms of the different nature (Coulomb interactions and overlaps) of these transitions in the valence and core cases. The polarization dependences of the core-ionization resonances, as well as the angular distributions of photoelectrons from the valence-coupled shape resonances, show clearly that the molecular axis of CO is essentially perpendicular to the surface in both adsorbate cases.

Oxygen-induced CO reorientation on Cr(110)

Studies of CO and CO/O chemisorption on Cr(110) at 120 K using high resolution electron energy loss spectroscopy (EELS), electron stimulated desorption ion angular distributions (ESDIAD), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES) are reported. On the clean surface, two molecular binding modes are sequentially populated. The first mode (α1CO) consists of molecules bound with the CO axis nearly parallel to the surface and saturates with the formation of a c(4×2) overlayer, whereas the second mode (α2CO) is comprised of CO oriented perpendicular to Cr(110). Predosing Cr(110) with atomic oxygen inhibits the α1CO mode such that for θ0 above ∼1/2 monolayer, only the α2CO mode is populated. More surprisingly, the c(4×2)α1CO overlayer is converted to disordered α2CO by subsequent addition of oxygen, implying a significant reorientation of the adsorbed molecules at 120 K.

Reactions of some iron and tungsten mercapto-complexes with electrophilic acetylenes leading to novel metallacycles. The crystal and molecular structure of the η2-vinyl complex [W{η2-C(CF3)C(CF3)C(O)SMe}(CO)2(η5-C5H5)

Reactions of [Fe(SR′)(CO)2(η5-C5H5)] with activated alkynes CF3CCCF3 and MeO2CCCCO2Me give heterocyclic complexes [[graphic omitted]R′}(CO)(η5-C5H5)](R′= alkyl or aryl, R = CF3 or CO2Me). Related derivatives [[graphic omitted]R′}(CO)2(η5-C5H5)](R′= Me or Et) obtained from [W(SR′)(CO)3(η5-C5H5)] and the alkynes in hexane at 20 °C undergo a sequence of thermal isomerisations above 25 °C involving initially a novel 1,3 shift of the SR′ ligand across the eneone ligand to give the η2-vinyl complex [W{η2-C(R)C(R)C(O)SR′}(CO)2(η5-C5H5)](R = CF3 only) followed by S-bonded vinyl ketone complexes [[graphic omitted]R′}(CO)2(η5-C5H5)] and ultimately O-bonded vinyl ketone derivatives [[graphic omitted]}(CO)2(η5-C5H5)] and co-ordinatively unsaturated alkyne complexes [W(SR′)(CO)(RCCR)(η5-C5H5)](R = CF3 only). An X-ray structure determination of the η2-vinyl complex [W{η2-C(CF3)C(CF3)C(O)SMe}(CO)2(η5-C5H5)] reveals the first example of a vinyl group bonded to a metal via both carbon atoms and therefore acting as a three-electron donor ligand. The structure consists of an approximately octahedrally co-ordinated tungsten atom bonded to an η5-C5H5 ligand which occupies one face of the octahedron. Two carbonyl ligands occupy two octahedral sites while the third is occupied by the η2-C(CF3)C(CF3)C(O)SMe ligand which adopts an orientation such that the vinylic C–C axis lies approximately parallel to one of the W–CO axes.

The structure of Rh(111)(2 × 2)-3CO from LEED intensities: Simultaneous bridge and near-top adsorption in a distorted compact hexagonal CO overlayer

The first Low-Energy Electron Diffraction (LEED) intensity analysis of molecular adsorption in multiple sites is presented. A 3 4 monolayer CO overlayer on Rh(111) is found to involve one bridge site and two near-top sites in each unit cell, which supports the bridge and top assignment based on earlier High-Resolution Electron Energy Loss Spectroscopy (HREELS) data. The near-top site is asymmetrical, with the CO axis close to the surface normal (but possibly tilted about 5°), yielding a bent Rh-C-O species. The near-top CO molecules are forced sideways from the ideal top site by ~ 0.53 Å due to bridge-bonded CO molecules located at a distance of 2.85 Å. This short CO-CO separation is somewhat smaller than corresponding intermolecular separations found in metal carbonyl clusters and crystalline CO and CO 2. The resulting CO overlayer has a hexagonal geometry that is distorted both parallel and perpendicular to the surface due to the strong metal-CO bonding. The Zanazzi-Jona and Pendry R-factors for the best structure are 0.25 and 0.47, respectively. The LEED analysis exhibits the use of different levels of approximation in the multiple scattering theory in order to show the value of approximate but fast calculations in preliminary structural searches. A new algorithm to obtain experimental I– V curves from digitized images of LEED patterns is described.

Surface phase transitions in CO chemisorption on Pt{110}

Abstract The chemisorption of CO on Pt{110} results in various coverage dependent phases. These have been investigated both during adsorption at 300 K and during desorption by means of continuous monitoring of LEED beam intensities, the CO derived levels in ARUPS, and thermal desorption spectra. We find that at very low coverages, isolated species on the reconstructed Pt{110}−(1 × 2) surface coexist with islands of CO on Pt{110}−(1 × 1). At higher coverages (⩾0.5), when the (1 × 2)→(1 × 1) transition is completed, repulsive interactions between nearest neighbour CO molecules result in a second state in the desorption spectra. Defect sites due to imperfect lifting of the surface reconstruction by CO inhibit the formation of the ordered phase at 300 K as the coverage approaches 1. Once these imperfections have been removed, a well ordered phase, designated (2 × 1) p1g1, can be formed. The “(2 × 1)” → (1 × 1) order-disorder transition is reversible. The CO axis is tilted away from the surface normal within the islands and the pigl phase. At all coverages CO is adsorbed into “on-top” sites as inferred from HREELS.

Surface phase transitions in co chemisorption on pt{110}

The chemisorption of CO on Pt{110} results in various coverage dependent phases. These have been investigated both during adsorption at 300 K and during desorption by means of continuous monitoring of LEED beam intensities, the CO derived levels in ARUPS, and thermal desorption spectra. We find that at very low coverages, isolated species on the reconstructed Pt{110}−(1 × 2) surface coexist with islands of CO on Pt{110}−(1 × 1). At higher coverages (⩾0.5), when the (1 × 2)→(1 × 1) transition is completed, repulsive interactions between nearest neighbour CO molecules result in a second state in the desorption spectra. Defect sites due to imperfect lifting of the surface reconstruction by CO inhibit the formation of the ordered phase at 300 K as the coverage approaches 1. Once these imperfections have been removed, a well ordered phase, designated (2 × 1) p1g1, can be formed. The “(2 × 1)” → (1 × 1) order-disorder transition is reversible. The CO axis is tilted away from the surface normal within the islands and the pigl phase. At all coverages CO is adsorbed into “on-top” sites as inferred from HREELS.

Effect of temperature on the ventilation response curve to carbon dioxide in anaesthetized cats

Effects of body temperature on the ventillatory control system were studied in 17 anaesthetized cats. At different body temperatures (stabilized within 0.1 °C) CO 2 response curves were measured in each cat. In with chloralose-urethan anaesthetized cats it was found that in the body temperature range of 34–40 °C, in which neither shivering nor panting occurred, no statistically significant trend with temperature was found in the slope (S) and the extrapolated intercept on the Pa CO 2 -axis (B) of the linear CO 2 response curve during hyperoxia as well as hypoxia. In two with pentobarbital anaesthetized cats similar results were obtained. The resting ventilation (at F i CO 2 = 0 ) did not change significantly, while the resting Pa CO 2 during hyperoxia showed a trend to increase with temperature just reaching the level of significance ( P < 0.05). Breathing frequency increased significantly with temperature ( P < 0.0005). When body temperature was elevated above 41 °C both the slope (S) and the intercept of the CO 2 response curve (B) decreased. In three cats ventriculo-cisternal perfusion was performed and no apparent influence of body temperature was found on the relation between the Pcsf CO 2 and on the V̇e-Pcsf CO 2 response curves. These findings show that body temperature has no important modifying effect on the ventilatory responding to CO 2 in anaesthetized cats in the temperature range of 34–40 °C.

Molecular and crystal structure of cis-[Co III(3-hydroxyimino-2,4-pentanedionato) 2(pyridine) 2] ClO 4

The crystal structure of cis[Co III(3-hydroxyimino-2,4-pentanedionato) 2(pyridine) 2]ClO 4 has been determined by X-ray analysis. The brown hexagonal tabular crystal are orthorhombic and the space group Pna2 1. The unit cell dimensions are a = 17.11(1), b = 10.62(2), c = 13.65(1) Å; Z = 4. The structure was deduced by the heavy atom method and refined by the block-diagonal least-squares method to a final R value of 0.090 for 1812 observed reflections. The structure consists of the complex cation with a cis geometry and the perchlorate anion. The cobalt atom has an octahedral coordination with the two CoN(pyridine) bond distances of 1.99 and 1.99 Å, and the two CoN (hydroxyiminato) bond distances of 1.88 and 1.90 Å, and the two CoO bond distances of 1.88 and 1.88 Å. Each of the planes of pyridine rings in the complex cation is almost perpendicular to each of the corresponding equatorial planes. The axial pyridine plane does not exactly bisect OCoN angle on the equatorial plane: it rotates about the axis of CoN (pyridine) in the range of 6° to 24° from the bisector of OCoN angle toward the CoO bond.

Chemisorption of co on clean and carbonized osmium

Photoemission and desorption studies indicate that CO is molecularly adsorbed on clean Os while adsorption of CO on a carbonized Os surface produces a different CO structure, Spectral data for this structure are consistent with molecular adsorption in which the CO axis is nearly parallel to the surface and both C and O are involved in bonding.

Electron paramagnetic resonance crystallography of 17O-enriched oxycobaltomyoglobin: stereoelectronic structure of the cobalt dioxygen system.

An electron paramagnetic resonance crystallographic study was made on oxycobaltomyoglobin with the dioxygen ligand enriched to 19.1% in (17)O. There are two spectroscopically distinct cobalt dioxygen species. The less abundant species, II (40%), has nonequivalent oxygen atoms with superhyperfine tensors (O)A(alpha) = (5, -67.5, 22.4)G and (O)A(beta) = (5.4, -83.3, 30.3)G. Together with the previously reported (59)Co hyperfine tensor [Chien, J. C. W. & Dickinson, L. C. (1972) Proc. Natl. Acad. Sci. USA 69, 2783-2787], the orbital spin densities are found to be O(alpha)(p(eta)) = 0.48, O(alpha)(p(zeta)) = -0.11, O(beta)(p(eta)) = 0.74, O(beta)(p(zeta)) = -0.16, Co(d(xz)) = -0.01, Co(d(yz)) = 0.06 for a total electron density of 1.01. The O-O axis is directed toward His-E7, suggesting a possible hydrogen bonding interaction which may contribute to the nonequivalency of the oxygen atoms; its projection approximately bisects N(1)-Fe-N(2). The z axis of the (Co)A tensor is tilted at an angle of 28 degrees from the heme normal, resulting in a Co-O-O angle of 120 degrees . The more abundant species, I (60%), has equivalent oxygen atoms with (O)A(gamma) = (12, -72.5, 20)G and orbital spin densities of O(gamma)(p(eta)) = 0.54, O(gamma)(p(zeta)) = -0.05, Co(d(xz)) = -0.02, Co(d(yz)) = 0.09 for a total spin density of 1.10. Although the direction cosines for this molecule cannot be precisely determined, the projection of its O-O axis approximately bisects N(2)-Fe-N(3) and is parallel to the imidazole ring of His-F8. Increase of temperature changes g, (Co)A, and (O)A values, with the largest effect seen with (O)A. This temperature dependence indicates averaging of the two bond structures which are stabilized at 77 K.

The geometry of CO on Ru(001): Evidence for bending vibrations in adsorbed molecules

As a test of the utility of the ESDIAD method (Electron Stimulated Desorption Ion Angular Distributions) in studies of the geometry of adsorbed molecules, the chemisorption of CO on Ru(001) has been examined. Data previously reported using UPS (ultraviolet photoemission spectroscopy) and EELS (electron energy loss spectroscopy) have indicated that CO is terminally bonded to the Ru surface through the C atom, with the CO axis perpendicular to the surface. The ESDIAD results for CO confirm this orientation; for all CO coverages in the temperature range 90 K to ~ 350 K, the angular distributions of O + and CO + ESD ions are centered about the surface normal. The widths of the ion beams are temperature dependent; for both O + and CO +, the half widths at half maximum, α, of the ion cones are ~16° at 300 K, and ~12° at 90 K. This temperature dependence, coupled with a simple model calculation, indicates that the dominant factors contributing to the width of the ESD ion beams are the CO surface bending vibrations, i.e., initial state effects. Thus, the data suggest that both the directions and widths of ESDIAD beams are determined largely by the structure and dynamics of the initial adsorbed state.

The solvation structure of Li+ dissolved in formic acid. A nuclear magnetic relaxation study combined with LCGO‐MO‐SCF calculations

AbstractIn connection with previous quantum chemical calculations the question arose whether in the solvation complex of Li+ in formic acid this cation is located between the CH hydrogen and the carbonyl oxygen or whether it is at the carboxyl oxygen on the CO axis. This question has been decided in the latter sense by 7Li magnetic relaxation time measurements. For the evaluation of the experimental data the information is needed whether in the solvation system the acid molecule exists in the H – H trans or cis form. LCGO‐MO‐SCF calculations show that the trans form is more stable. The experimental procedure is based on the isotopic substitution technique.

ChemInform Abstract: THE CRYSTAL STRUCTURE OF TRICHLOROTIN‐PENTACARBONYLMANGANESE, CL3SN‐MN(CO)5

The crystal structure of trichlorotin–pentacarbonylmanganese, Cl3Sn–Mn(CO)5, has been determined by means of X-ray diffraction. The crystal is monoclinic; a=14.10(1), b=13.38(5), c=13.27(2) A, and β=97.39(21)° with the P21/c space group and with Z=8. The structure, established by the heavy-atom method, has been refined by a least-squares method based on 2581 reflections collected by diffractometry to give an R value of 10%. The asymmetric unit contains two quite similar molecules. The geometry around the tin atom is distorted tetra-hedrally, while the manganese atom exhibits a distorted octahedral coordination. The four equatorial carbonyl groups are displaced from the equatorial plane toward the tin atom. There is an approximate mirror plane through the Sn–Mn–CO(axial) axis. The Sn–Mn bond distance, 2.590(5) A, is shorter by about 0.08 A than that of the triphenyl and trimethyl analogues. The mean Mn–C distance of 1.87 A is longer than that of the trimethyl analogue. These changes in bond distances may b...

The Crystal Structure of Trichlorotin–pentacarbonylmanganese, Cl3Sn–Mn(CO)5

Abstract The crystal structure of trichlorotin–pentacarbonylmanganese, Cl3Sn–Mn(CO)5, has been determined by means of X-ray diffraction. The crystal is monoclinic; a=14.10(1), b=13.38(5), c=13.27(2) Å, and β=97.39(21)° with the P21/c space group and with Z=8. The structure, established by the heavy-atom method, has been refined by a least-squares method based on 2581 reflections collected by diffractometry to give an R value of 10%. The asymmetric unit contains two quite similar molecules. The geometry around the tin atom is distorted tetra-hedrally, while the manganese atom exhibits a distorted octahedral coordination. The four equatorial carbonyl groups are displaced from the equatorial plane toward the tin atom. There is an approximate mirror plane through the Sn–Mn–CO(axial) axis. The Sn–Mn bond distance, 2.590(5) Å, is shorter by about 0.08 Å than that of the triphenyl and trimethyl analogues. The mean Mn–C distance of 1.87 Å is longer than that of the trimethyl analogue. These changes in bond distances may be interpreted in terms of the π-interaction between the two metal atoms, which is more pronounced in the chloro-derivative than in the methyl derivative.

ChemInform Abstract: ORIENTATION EFFECTS IN TRIPLET‐TRIPLET ENERGY TRANSFER FROM BENZOPHENONE TO PHENANTHRENE BY PHOTOSELECTION STUDIES

The method of photoselection has been used to measure the degrees of polarisation for benzophenone and phenanthrene phosphorescence in poly(methyl methacrylate)(PMMA) at room temperature and 77 K. These measurements are compared with the degrees of polarisation of benzophenone phosphorescence and sensitised phenanthrene phosphorescence obtained upon selective excitation of benzophenone in a mixture of benzophenone and phenanthrene in PMMA. The studies indicate that if an orientation effect exists for triplet–triplet energy transfer it is a slowermoving function than the square of the sine of the angle between the CO axis of benzophenone and the normal to the molecular plane of phenanthrene. The results of photoselection and magnetophotoselection studies are compared with studies of intramolecular energy transfer between chromophores of known molecular orientation.

Orientation effects in triplet–triplet energy transfer from benzophenone to phenanthrene by photoselection studies

The method of photoselection has been used to measure the degrees of polarisation for benzophenone and phenanthrene phosphorescence in poly(methyl methacrylate)(PMMA) at room temperature and 77 K. These measurements are compared with the degrees of polarisation of benzophenone phosphorescence and sensitised phenanthrene phosphorescence obtained upon selective excitation of benzophenone in a mixture of benzophenone and phenanthrene in PMMA. The studies indicate that if an orientation effect exists for triplet–triplet energy transfer it is a slowermoving function than the square of the sine of the angle between the CO axis of benzophenone and the normal to the molecular plane of phenanthrene. The results of photoselection and magnetophotoselection studies are compared with studies of intramolecular energy transfer between chromophores of known molecular orientation.

The electronic absorption spectra of the 2, 5-diketopiperazine single crystal and evaporated film

The polarized absorption spectrum of the single crystal of 2,5-diketopiperazine was measured in the wavelength region from 250 to 160 nm by the use of a vacuum ultraviolet microspectrophotometer constructed in our laboratory, and three absorption bands were found. The weak band at 202 nm polarized perpendicular to the molecular plane was assigned to the n → π* transition. The moderately strong band at 187 nm was found to be polarized almost parallel to the CO axis and was tentatively assigned to the n → σ* transition. The absorption band at 160 nm region was interpreted to be the first π → π* band from the polarization direction and the intensity. All the three bands shift appreciably to blue by the hydrogen bonding formation.

Preferential Orientation of CO Adsorption on Ni as Determined by Extended Hückel Calculations

The adsorption of CO on the nickel surface has been calculated using a modified extended Huckel technique for a number of different orientations of the CO with respect to the nickel surface. The calculations show that double site adsorption with the CO molecule normal to the surface and the carbon atom closest to the metal gives the most stable configuration (2.57 eV). The single site absorbs with an energy of 2.39 eV. However, other configurations also give fairly large bonding energies. The CO normal to the surface with oxygen closest to the metal gives a heat of adsorption of 0.37 eV. Two-center adsorption with the CO axis parallel to the surface and the molecule symmetrically placed between the nearest neighbors gives a chemisorption energy of 1.34 eV. These values compare with an experimental value of 1.98 eV. It is interesting to note that when the CO bond is stretched 10% in the latter configuration the total energy of the system decreases rather than increases.

The 2670 Å absorption system of formyl fluoride

A new analysis of the 2670 Å absorption spectrum of formyl fluoride is presented. Many temperature dependent bands are observed for the first time. The electronic origins of HCOF and DCOF are located at 37 488 and 37 504 cm −1. The spectrum is assigned to a transition between a planar ground state 1 A′, of symmetry group C s , and a pyramidal excited state 1 A, of symmetry group C 1, with the out-of-plane angle between the CO axis and the HCF plane in the range 30 to 35°. Inversion doubling leads to measurable splitting for bands with 2, 3 (1 +, 1 −) and 4, 5 (2 +, 2 −) quanta of the CH out-of-plane bending mode, ν 6′, excited. Transitions from the vibrationally excited ground state give the first direct experimental measurement of ν δ″ for HCOF, 1010 cm −1.