Copyright (c) 2010 All rights reserved. http://works.bepress.com/rkoob Recent documents in Robert D. Koob en-us Wed, 21 Jul 2010 14:53:46 PDT 3600 http://works.bepress.com/rkoob/7 http://works.bepress.com/rkoob/7 Thu, 08 Jan 2009 16:51:58 PST Propane has been photolyzed at 123.6 nm, in the presence and absence of O2, at pressures from 2–380 Torr. All products except ethane exhibit a pressure dependence which is attributed to secondary dissociation of the primary fragments, H2, CH4, C2H4, and C3H6. It is assumed that the range of energies carried by these fragments is broad enough that some will not dissociate even at low pressures while others of the same species cannot be stabilized even at high pressures. An internally consistent analysis rationalizes the entire observed product spectrum, with some uncertainty arising from an ambiguity in the source of acetylene. The following primary quantum yields, prior to secondary dissociation, are estimated: C3H8 + hv = H2 + C3H6        φ = 0.42 mol/einstein                    = C2H4 + CH4     φ = 0.47 mol/einstein                    = CH2 + C2H6     φ = 0.09 mol/einstein James H. Vorachek Articles http://works.bepress.com/rkoob/6 http://works.bepress.com/rkoob/6 Thu, 08 Jan 2009 16:19:08 PST The molecular structures and bond energies in the low-lying excited states of n-alkanes from methane to n-pentane are investigated using the semi-empirical INDO method with configuration interaction. In general the calculated geometries and bond energies are consistent with the known threshold photochemistry of these molecules, the only exception being the prediction of vicinal (rather than geminal) elimination of H2 in ethane. It appears that INDO overestimates the amount of angular distortion in these excited states. Patrick M. Saatzer Articles http://works.bepress.com/rkoob/5 http://works.bepress.com/rkoob/5 Thu, 08 Jan 2009 16:19:04 PST The yields of ionic and excited molecule reactions in -radiolysis of liquid propane from 35 to –130°C have been assessed by isotopic analysis of C3H8+ C3D8+ O2 and CH3CD2CH3+ O2mixtures. From a comparison with gas phase data the following conclusions are reached for the gas to liquid phase change : (a) the ionic decomposition yield decreases by ≤ 69%, (b) the net excited molecule decomposition yield decreases by 7% or less, (c) parent ion fragmentation still occurs in the liquid and exhibits fragmentation processes requiring from 1-4 eV excitation, (d) the H–2/H– transfer reaction ratio for C2H+4+ C3H8 seems to be increased, and (e) the isotopic decomposition of CH3CD2CH3 is drastically changed. Robert D. Koob Articles http://works.bepress.com/rkoob/4 http://works.bepress.com/rkoob/4 Thu, 08 Jan 2009 16:19:00 PST The radical reactions in the liquid phase γ-radiolysis of propane have been studied from –130 to 35°C and compared with the gas-phase radiolysis at 35°C. Oxygen was used as a scavenger to separate thermal radical yields, and effects of phase and temperature on the radical yields were assessed. The gas-liquid phase change(a) decreases total decomposition by about 14%,(b) increases disproportionation/combination (D/C) ratios for all radicals by 30% and (c) decreases the isopropyl/n-propyl radical ratio. The decrease in liquid temperature (a) changes the predominant reaction of H atoms from abstraction from propane to addition to product propylene below –78°C at doses of 1 Mrad, (b) increases the D/C ratios by 31% and (c) decreases the isopropyl/n-propyl radical ratio. Dose effects were briefly studied; they are complex and cannot be explained by radical reactions alone. Robert D. Koob Articles http://works.bepress.com/rkoob/3 http://works.bepress.com/rkoob/3 Thu, 08 Jan 2009 16:18:57 PST Studies of several coal-mining sites in western North Dakota have resulted in the development of a hydrogeochemical model which accounts for the observed chemical characteristics of subsurface water in undisturbed settings. Critical hydrogeochemical processes include sulfide oxidation, gypsum precipitation and dissolution, carbonate mineral dissolution and cation exchange.In the semi-arid climate of western North Dakota, the near-surface several meters of the landscape is constantly subjected to alternate wetting/drying. This mechanism is the key to hydrogeochemical evolution of both pore water in the rooting zone and subsurface water that eventually reaches the water table.Recent refinements in the hydrogeochemical model have focused on the sulfur cycle and determination of the applicability of the model to postmining (spoils) landscapes. Field activities have included detailed groundwater instrumentation of undisturbed and spoils areas at two geologically distinctive mine sites in western North Dakota. Refinement of the model included analyses of the texture, bulk mineralogy, clay mineralogy, sulfide abundance, and sulfur concentration in overburden core samples. Laboratory experiments were designed to determine the source and mechanisms of sulfate salt production from overburden samples.From the study we conclude that the hydrogeochemical model is equally applicable to undisturbed and spoils landscapes and that the major species of concern in this region are sodium and sulfate. This research indicates that the major source of sulfate is sulfides in the overburden and that the solubility of sulfate in groundwater in these settings is largely controlled by the sodium/calcium ratio.We also conclude that negative hydrogeochemical impacts resulting from surface mining in the Northern Great Plains will include increased mineralization of groundwater and sodic and salt effects on plants. The degree of these impacts will be dependent upon site· specific hydrogeological, geochemical, and mineralogical variables. A consideration of these non-soils aspects of surface-mined lands thus is essential to proper surface-mine reclamation design in this region. Gerald H. Groenewold Articles