Cadmium metal nanocrystallites (NCs), prepared on graphite surfaces by electrochemical deposition, are employed as precursors to synthesize core−shell nanoparticles consisting of a crystalline cadmium sulfide (CdS) core and a sulfur or polysulfide shell. Core−shell NCs having a large CdS core (radii R CdS > 40 Å) were prepared by exposing electrodeposited cadmium particles (R Cd > 25 Å) to H2S at 300 °C, whereas nanoparticles having a smaller CdS core (down to 17 Å) were obtained from cadmium precursor particles via a Cd(OH)2 intermediate. For both large-core and small-core CdS nanoparticles, the addition of the sulfur capping layer (ranging in thickness from 5 to 30 Å) occurred during exposure to H2S at 300 °C. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) data show that the synthesis of CdS NCs proceeded on a particle-by-particle basis such that the particle size and monodispersity of the CdS core were directly related to those of the cadmium metal precursor particles electrodeposited in the first step of the synthesis. The CdS cores of these particles were found by electron diffraction to be epitaxially aligned with the hexagonal periodicity of the graphite surface and oriented with the c-axis of the wurtzite unit cell perpendicular to the surface. The low-temperature photoluminescence (PL) spectra for CdS nanocrystals without the sulfur capping layer were dominated by broad trap state emission peaks. In contrast, the PL spectra for sulfur-passivated CdS NCs were characterized by a prominent exciton emission band and much weaker trap state emission peaks. As the radius of the CdS core was reduced from 50 to 17 Å, the energy of the exciton emission peak shifted from the macroscopic value of 2.56 to 3.1 eV in excellent agreement with the predictions of the Coulomb-corrected, effective mass model.

Abstract. The uptake of sulfur dioxide (SO2) on synthetic sea salt (SSS) and its components, NaC1 and MgCI2o6H20, was studied at 298 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. Significant uptake on dried salts was not observed, placing upper limits on the uptake coefficients, ¾, of < 1 x 10-4 for NaCI, < 5 x 10-4 for MgC12-6H20, and < 8 x 10-5 for SSS. However, SSS and MgCI2o6H20 that had not been dried before use showed significant uptake of SO2. The magnitude of the uptake depended strongly on the exposure time and the amount of water desorbing. Initially, the measured uptake coefficients for SO2 on SSS were as high as 0.09, but they rapidly decreased below 10-2 with a t-l/2 dependence as expected for approach to the equilibrium saturation concentration in an aqueous solution. The decreasing uptake coefficient slowly approaches zero over hours, consistent with reactions in a water layer with species such as CaCO3. The products of the reaction were shown by diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) to include low solubility metal sulfites. These studies show that uptake of SO2 on sea salt particles, even below their deliquescence/effiuorescence points, can be treated as if it is into an aqueous salt solution.

Volatile organic compounds emitted from a several decade series of bound periodicals (1859-1939) printed on ground wood paper, as well as historical books dating from the 1500s to early 1800s made from cotton/linen rag, were studied using an improved headspace SPME/GC-MS method. The headspace over the naturally aging books, stored upright in glass chambers, was monitored over a 24-h period, enabling the identification of a wide range of organic compounds emanating from the whole of the book. The detection of particular straight chain aldehydes, as well as characteristic alcohols, alkenes and ketones is correlated with oxidative degradation of the C(18) fatty acid constituency of paper. The relative importance of hydrolytic and oxidative chemistry involved in paper aging in books published between 1560 and 1939 was examined by comparing the relative abundances of furfural (FUR) a known cellulose hydrolysis product, and straight chain aldehydes (SCA) produced from the oxidation of fatty acids in paper. The relative abundance of furfural is shown to increase across the 379-year publication time span. A comparison of relative SCA peak areas across the series of books examined reveals that SCA emission is more important in the cotton/linen rag books than in the ground wood books.

The absorption cross sections for gaseous ClNO2 in the 200–370 nm region and for Cl2 in the 270–400 nm region have been determined at 298 K. The cross sections for Cl2 are in excellent agreement with the literature. At λ < 300 nm the absorption cross sections for ClNO2 are in good agreement with those of lilies and Takacs (1976/1977) and Nelson and Johnston (1981) but are higher than those of Martin and Gareis (1956) from 220 to 240 nm. In the tropospherically important region beyond 290 nm our results, which have been corrected for impurity Cl2 using a combination of mass spectrometry and UV absorption, fall between those of Martin and Gareis (1956) and lilies and Takacs (1976/1977) and are in excellent agreement with the values of Nelson and Johnston (1981). Estimates of the photolysis rate constants and photolytic lifetimes for ClNO2 for various solar zenith angles at the Earth's surface are reported. It is shown that atomic chlorine from ClNO2 photolysis may be a significant initiator of organic photooxidation in both moderately polluted and remote marine atmospheres.

We report a study of the photochemistry of Mo(CO)~ in the gas phase. Time-resolved infrared laser absorption spectroscopy is used to monitor the.vibrationa1 spectroscopy and lifetimes of the coordinatively unsaturated species formed upon photolyses at 351, 248, and 193 nm. The infrared spectra observed indicate that MO(CO)~ has C , symmetry, Mo(CO), has C , symmetry, and Mo(CO), has C, , symmetry. All three unsaturated species undergo rapid association reactions with Mo(CO)~ and with CO. MO(CO)~ recombines with CO with a high-pressure limiting rate constant of 2.0 (*0.2) X lo6 Torr-l s-l. The corresponding rate constants for Mo(CO)~ and Mo(CO), are 7.5 (&1.5) X lo6 and 1.8 (fl.O) X lo7 Torr-ls-', respectively. Mo, etc.), have been reported to catalyze reactions such as the (2) Masters, C. Homogeneous Transition Metal Catalysis; Chapman and (1) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles

Ambient ionization processes are becoming more widely used for the measurement of atmospherically relevant particles and gases. We report here ambient ionization mass spectra utilizing a commercial tincture of iodine and a piezoelectric discharge gun (PDG) to generate the ionizing reagents. Analytes include Cl 2 , Br 2 , HNO 3 , the C 1 −C 9 series of saturated monocarboxylic acids, benzoic acid, 2,2-dimethylpropanoic acid, 9-decenoic acid, and trichloroacetic acid. While Cl 2 and Br 2 form the [M + I] − iodide adducts, HNO 3 and the organic acids show unexpected peaks corresponding to [2M − 2H + I] −. For HNO 3 , the new ion formed is interpreted as the [NO 3 − •••IONO 2 ] complex, where IONO 2 is likely formed upon reaction of HOI with gaseous NO 3 −. Similarly, for the organic acids, the [2M − 2H + I] − peaks are interpreted as [RC(O)O − •••IOC(O)R] complexes formed by association of RC(O)O − with acyl hypoiodites [RC(O)OI]. It is proposed that the association of (1) Cl 2 and Br 2 with I − , (2) IONO 2 with NO 3 − ions, and (3) RC(O)OI with carboxylate ions occurs via non-covalent halogen bonding. The results suggest the possibility that halogen bonding may play a role in chemical transformations in the atmosphere, particularly in particles where concentrations of iodinated species may be significant.

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