Fund, and the allocation of computer time from the Computer Center of the University of New Brunswick. functional approximation used in the computations. There are very few computations for arene-metal complexes that are of sufficient quality to predict their bond and total energies accurately. In order to determine whether the LCAO-LSD method can generally predict these properties, more computations on a whole series of arene-metal compounds must be performed and compared with accurate experimental data.The magnetic circular dichroism (MCD) and absorption spectra of zinc phthalocyanine (ZnPc) isolated in an Ar matrix have been studied over the range 14700-74000 cm-I. Synchrotron radiation, from the electron storage ring at the Synchrotron Radiation Center, Madison, WI, was used for energies above 33 000 cm-I. The spectra are well resolved, and the MCD permits the determination of excited-state magnetic moments. There is strong evidence that the Pc rings are preferentially oriented with the molecular planes parallel to the deposition window. The data can be reasonably correlated with the old Peel calculation of Henriksson et al., but there is a compelling need for a new calculation that extends to higher energy and includes extensive configuration interaction. (4) Bondybey, V. E.; English, J. H. J . Am. Chem. SOC. 1979, 101, (5) Huang, T. H.; Reickhoff, K. E.; Voigt, E. M. J. Chem. Phys. 1982, (6) Huang, T. H.; Rieckhoff, K. E.; Voigt, E. M.

The reaction of gold substrates with p-nitrobenzene diazonium tetrafluoroborate (NBD) in 0.1 M H(2)SO(4) at open-circuit potential (OCP) is demonstrated to proceed by electron transfer from gold to the NBD cation. Electrochemical, atomic force microscopy, and X-ray photoelectron spectroscopy analyses reveal the formation of multilayer films with the same composition as electrografted films. The film growth characteristics (surface concentration and film thickness vs time) also follow those observed during electrografting, consistent with electron transfer from the substrate to the diazonium cation. The OCP of the gold substrate increases during the period of film growth ( approximately 60 min) and then decreases to close to its initial value. The increase corresponds to accumulation of positive charge as electrons are transferred to NBD; the discharge process is tentatively attributed to slow oxidation of adventitious impurities in the reaction solution. Films formed at OCP or by electrografting from aqueous acid solution are markedly less stable to sonication in acetonitrile than are those electrografted from acetonitrile. Increased amounts of physisorbed material in films prepared in aqueous media or bonding of aryl groups to different gold sites in the two media are tentatively proposed to account for the different stabilities.

Abstract. Through the 21st century, anthropogenic emissions of the greenhouse gases N 2 O and CH 4 are projected to increase, thus increasing their atmospheric concentrations. Consequently, reactive nitrogen species produced from N 2 O and reactive hydrogen species produced from CH 4 are expected to play an increasingly important role in determining stratospheric ozone concentrations. Eight chemistry-climate model simulations were performed to assess the sensitivity of stratospheric ozone to different emissions scenarios for N 2 O and CH 4 . Global-mean total column ozone increases through the 21st century in all eight simulations as a result of CO 2 -induced stratospheric cooling and decreasing stratospheric halogen concentrations. Larger N 2 O concentrations were associated with smaller ozone increases, due to reactive nitrogen-mediated ozone destruction. In the simulation with the largest N 2 O increase, global-mean total column ozone increased by 4.3 DU through the 21st century, compared with 10.0 DU in the simulation with the smallest N 2 O increase. In contrast, larger CH 4 concentrations were associated with larger ozone increases; global-mean total column ozone increased by 16.7 DU through the 21st century in the simulation with the largest CH 4 concentrations and by 4.4 DU in the simulation with the lowest CH 4 concentrations. CH 4 leads to ozone loss in the upper and lower stratosphere by increasing the rate of reactive hydrogen-mediated ozone loss cycles, however in the lower stratosphere and troposphere, CH 4 leads to ozone increases due to photochemical smogtype chemistry. In addition to this mechanism, total column ozone increases due to H 2 O-induced cooling of the stratosphere, and slowing of the chlorine-catalyzed ozone loss cycles due to an increased rate of the CH 4 + Cl reaction. Stratospheric column ozone through the 21st century exhibits a near-linear response to changes in N 2 O and CH 4 surface concentrations, which provides a simple parameterization for the ozone response to changes in these gases.

The covalent grafting of nitrophenyl functionalities to planar carbon substrates by reaction with 4-nitrobenezene diazonium salt at open circuit potential has been studied in aqueous acid and acetonitrile solutions. Atomic force microscopy and electrochemical measurements reveal that the reaction proceeds through two distinct mechanisms. Rapid film growth occurs via reduction of the 4-nitrobenezene diazonium cation by the substrate, giving an aryl radical that couples to the surface. Film growth by this mechanism ceases once the film has reached a thickness at which electron transfer through the passivating film is no longer possible. Slow film growth via a secondary, potential-independent mechanism continues even after the substrate-dependent reaction has ceased. We tentatively propose that slow film growth involves grafting of an aryl cation originating from thermal heterolytic decomposition of the diazonium cation.

A range of synthetic carbonated apatites and human dental enamel have been studied at low temperatures (50 K) by laser Raman spectroscopy. The widths of the Raman spectral bands of hydroxyapatite were significantly reduced at low temperatures with the appearance of several peaks unobserved at room temperatures. The number of observed phosphate and hydroxyl ion Raman peaks was consistent with the space group P63. Spectra of carbonated apatites were not further resolved at low temperatures and Raman peak broadening due to loss of long-range translational order in the apatite structure was linearly correlated with the carbonate content of the sample. The same Raman peak broadening occurred in the spectrum of dental enamel. The number of carbonate bands in the Raman spectrum of carbonated apatites indicated that carbonate exists in two crystallographically distinct sites of different symmetry within the apatite structure.