Geochemical and physical analysis of the bedrock formations and lowest tills at the Wellsch Valley Site,Saskatchewan, Canada

Nine bedrock and two till samples were analyzed to determine whether their chemical and physical properties could be used to distinguish between bedrock units and to differentiate local bedrock from overlying tills. The bedrock samples came from The North Cliff subsite of the Wellsch Valley Site, and the till samples from Jaw Face subsite. Eight of the nine bedrock samples show great similarity. However, their geochemical differences from the overlying Quaternary tills establish that the tills contain much material entrained, during one or more early Quaternary glaciations, from older bedrock outcrops to the north and northeast. The glaciers that laid down the tills appear to have reworked and concentrated elements compatible with a dry climate, probably formed by weathering during long interglacial, and perhaps preglacial, intervals when the surface was undergoing slow degradation.     

Fluorescence from the second excited singlet of aromatic thioketones in solution

The spectral characteristics and the quantum yield of the fluorescence from the second excited singlet state S₂ of the aromatic thioketone molecules xanthione (XS) and thioxanthione (TXS) have been determined in solution at room temperature and 77 K. In 3-methylpentane, the measured quantum yields are φ_f (295 K) = 5.1 × 10^?3 and φ_f(77 K) = 1.0 × 10^?2 for XS, and φ_f (295 K) = 1.5 × 10^?3 and φ_f (77 K) = 2.5 × 10^?3 for TXS. Using the Strickler-Berg expression for the radiative lifetime, the decay rate of S₂ is derived. It is concluded that internal conversion S₂ ? S₁ is the dominating deactivation channel of S₂ with k^{77 K}_nr(S₂ ? S₁) = 1.0 × 10¹⁰ s^?1 for XS and k^{77 K}_nr (S₂→S₁) = 2.2 × 10¹⁰ s^?1 for TXS. Between 295 and 77 K, φ_f increases by a factor of about 2 following an Arrhenius type expression. This temperature dependence of φ_f is considered to be intramolecular in nature and is attributed to a temperature sensitive rate constant k_nr(S₂?S₁) with an activation energy of 190 ± 20 cm^?1 and a frequency factor k′_nr = 3 × 10¹⁰ s^?1 for the XS molecule in 3-methylpentane.     

Regioselective synthesis of substituted pyrroles: efficient palladium-catalyzed cyclization of internal alkynes and 2-amino-3-iodoacrylate derivatives

The first efficient and regioselective palladium-catalyzed cyclization of internal alkynes and 2-amino-3-iodoacrylates to give moderate to excellent yields of highly functionalized pyrroles has been developed. This approach is applicable to a range of alkynes and affords the deacylated pyrrole under reaction conditions for most substrates. [reaction: see text]     

Polygon containment under translation

The polygon containment problem is the problem of deciding whether a polygon P can be translated to fit inside another polygon P'. We present algorithms for two cases of the polygon containment problem: when both P and P' are rectilinearly convex, and when P is convex and P' is arbitrary. In both cases the algorithms run in time O(n²logn), where n is the sum of the number of bounding edges of the two polygons. Applications to an inspection problem and a stock-cutting problem are discussed, as is the containment problem when both P and P' are nonconvex.     

Gd2@C79N: isolation, characterization, and monoadduct formation of a very stable heterofullerene with a magnetic spin state of S = 15/2

The dimetallic endohedral heterofullerene (EHF), Gd(2)@C(79)N, was prepared and isolated in a relatively high yield when compared with the earlier reported heterofullerene, Y(2)@C(79)N. Computational (DFT), chemical reactivity, Raman, and electrochemical studies all suggest that the purified Gd(2)@C(79)N, with the heterofullerene cage, (C(79)N)(5-) has comparable stability with other better known isoelectronic metallofullerene (C(80))(6-) cage species (e.g., Gd(3)N@C(80)). These results describe an exceptionally stable paramagnetic molecule with low chemical reactivity with the unpaired electron spin density localized on the internal diatomic gadolinium cluster and not on the heterofullerene cage. EPR studies confirm that the spin state of Gd(2)@C(79)N is characterized by a half-integer spin quantum number of S = 15/2. The spin (S = ?) on the N atom of the fullerene cage and two octet spins (S = 7/2) of two encapsulated gadoliniums are coupled with each other in a ferromagnetic manner with a small zero-field splitting parameter D. Because the central line of Gd(2)@C(79)N is due to the Kramer's doublet with a half-integer spin quantum number of S = 15/2, this relatively sharp line is prominent and the anisotropic nature of the line is weak. Interestingly, in contrast with most Gd(3+) ion environments, the central EPR line (g = 1.978) is observable even at room temperature in a toluene solution. Finally, we report the first EHF derivative, a diethyl bromomalonate monoadduct of Gd(2)@C(79)N, which was prepared and isolated via a modified Bingel-Hirsch reaction.     

Stratigraphic and geochemical evidence for industrial pollutants in alpine and subalpine soils of the Wind River Mountains,Western Wyoming,USA

A stratigraphic and geochemical study of alpine soils, which formed in later Pleistocene (late glacial) and Neoglacial deposits in the Wind River Mountains of western Wyoming, indicates that these soils have been affected by air-fall influx of inorganic pollutants. Arsenic, bromine, and antimony appear to have been deposited in surface soils by incorporation of aeolian materials which were presumably transported by prevailing winds from industrial sources, including coal-burning operations. Because vanadium was not found in surface soils at concentrations above site-specific background levels, oil-fired energy generating stations were not deemed to be significant sources of surface soil pollution in the region. Acid-rain effects were not observed in the soils.     

Solvent effect on the non-radiative S2(ππ*) decay of xanthione

The fluorescence quantum yield of the S₂(ππ*) state of xanthione has been measured in various solvents at room temperature. With these data, the strong solvent effect on the subnanosecond, non-radiative S₂ decay has been assessed.     

Temperature dependence of radiationless processes. Isoquinoline in solution

The temperature dependence of the fluorescence quantum yield φ_f, the fluorescence lifetime τ_f, and the oscillator strength f(S₀→S₁) of isoquinoline in solution has been measured between room temperature and 77 K. Following an Arrhenius type expression, φ_f in ethanol increases from 0.012±0.002 at 295 K to 0.61±0.03 at 77 K paralleled by an increase of τ_f from 0.25±0.10 ns to 9.0±0.2 ns. Over the same temperature range f(S₀→S₁) and the radiative fluorescence lifetime remain constant. By analyzing the temperature dependent data, it is shown that a spin-allowed internal conversion process with an activation energy of ～1500 cm^?1 is responsible for the observed temperature effect. A mechanism is proposed based upon a thermally activated depopulation of the S₁(ππ^*) state of isoquinoline via a slightly higher state, presumably the S₂(ππ^*) singlet state. An extremenly fast process involving the dissociation of the hydrogen bond deactivates this latter state, by possing S₁.     

Geochemistry of Holocene and late Pleistocene soils in the Rouge River and Scarborough Bluffs areas,South-Central Ontario,Canada

Concentrations of major, minor and trace elements were measured in four soil profiles from south-central Ontario. The mean concentration values reported are probably representative of elemental levels in soils formed from sediments reworked by lacustrine and fluvial processes and weathered over the last 12 000 years. The older soils in the sequence (R12, R15 and BRIM1) show declining Na, K, and Al, mainly from Ca dilution, especially in the lower horizons. Iron and Mg levels were not affected by the variations in the Ca concentrations. Arsenic, Br, and Sb concentrations did not increase appreciably in surface A horizons, indicating no measurable airfall influx of industrial pollutants. The relative increase in Mn/Al in the lower horizons of the older soils may be related to leaching by soil or ground water movement.     

Geochemistry of later Pleistocene and Holocene palaeosols/soils in the Okstindan Mountains,Norway

Palaeosols and soils of early Holocene (9,000–10,000 yr BP) and Neoglacial (<1200 yr BP) ages from three sections in the Okstindan Mountains in central Norway were analyzed to determine their geochemical compositions. Four buried horizons and a surface sample all had significant water/organic contents. The highest Br (and also Th, U and possibly the REEs) contents were associated with the highest water/organic contents. From the rare earth and other elemental concentration variations, it appears that the three sections were formed from three parent materials, different horizons of which have been affected by weathering and plants.