Predicting arene rate coe ffi cients with respect to hydroxyl and other free radicals in the gas-phase : a simple and e ff ective method using a single
Predicting arene rate coefficients with respect to hydroxyl and other free radicals in the gas-phase: a simple and effective method using a single topological descriptor M. R. McGillen, C. J. Percival, G. Pieterse, L. A. Watson, and D. E. Shallcross School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, The Sackville Building, Sackville Street, P.O. Box 88, Manchester M60 1QD, UK Department of Air Quality and Climate Change, Energy Research Centre for the Netherlands, P.O. Box 1, 1755 ZG Petten, The Netherlands Biogeochemistry Research Centre, School of Chemistry, The University of Bristol, Cantock’s Close BS8 1TS, UK Received: 13 November 2006 – Accepted: 2 February 2007 – Published: 26 February 2007 Correspondence to: C. J. Percival (c.percival@manchster.ac.uk)
Can topological indices be used to predict gas-phase rate coefficients of importance to tropospheric chemistry? Reactions of alkenes with OH, NO3 and O3.
Rate coefficients for the gas-phase reactions of unsaturated hydrocarbons with OH, NO(3) and O(3) are of vital importance to atmospheric modelling. Many of these rate coefficients are unknown--possibly resulting from the variety of these compounds and the inherent expense of deriving these data experimentally--and a reliable method for their prediction would therefore be of value to such models. This study presents a method for estimating rate coefficients for C(2)-C(10) olefins. Measured rate coefficients for the reaction of unsaturated hydrocarbons with OH and NO(3) radicals and O(3) are correlated with the Randić topological descriptor and an established correlation parameter, i.e. ionization potentials calculated using the frontier molecular orbital (FMO) approach. Although the ionization potential method produces better correlations in general, OH correlations of aliphatic species, subdivided into groups of varying total number of primary (1 degree), secondary (2 degrees) and tertiary (3 degrees) carbon atoms (Sigma x degrees (x)) produced several new trends with the Randić index that were not present in the ionization potential correlations. Strong correlation was observed with a Randić-type index optimized to include a term for side chain length (Sigma x degrees (x)). The presence of strong relationships, made predictable by molecular constitution, makes topological descriptors a useful and accessible tool for estimating rate coefficients for the reactions of OH with aliphatic species. This study indicates that alkene reactivity is affected strongly by constitution and that abstraction as well as addition may be important for some classes of compound.
The Study of Relationship between Berm Width and Debris Flow at the Slope
The purpose of this study is to estimate the behavior and the mechanism of debris flow at the end of mountain side when a berm was set on the inclined plane. The numerical model was performed by using the Finite Difference Method(FDM) based on the equation for the mass conservation and momentum conservation. In order to measure the behavior of the debris flow, the debris flow of a straight channel slope and the debris flow of channel slope with 3 types of berms were compared. First, the flow discharge and the sediment volume concentration at the downstream of the channel slope, depending on the various berm width and the different inflow discharges at the upstream of the channel were analyzed. The longer the berm width, the flow discharge at the downstream of the channel was decreased and the high flow fluctuation was reduced by a berm. And it means that a berm can effect for the delay of the debris flow. Through Root Mean Square ratio(RMS) comparison, the flow discharge of the channel slope with a berm was lower than that of a straight channel slope. The longer the berm width, for the sediment volume concentration, an inflection point did not show but mild curve. Because the low sediment concentration with water mixture by a berm continuously flow at the downstream end, it will be effect for reducing the disaster caused by debris flow. The results of this study will provide useful information in predicting and preventing disaster caused by the debris flow.