Gilbert J. Mains

Flash Photolysis of Hydrogen Iodide in the Presence of Deuterated Hydrocarbons

The reactions of hot hydrogen atoms in the range 0.8–2.4 eV with perdeuterated and partially protonated hydrocarbons have been studied. The hot atoms were produced in C2D6, C3D8, n‐C4D10, and various isotopically mixed ethanes by flash photolyzing HI‐RHD mixtures. Graphs of product ratio H2/HD vs the initial reactant ratio HI/RD were characteristically linear. These and similar graphs for mixtures containing a rare gas were analyzed using the kinetic theory of hot‐atom reactions developed by Estrup and Wolfgang and also by a simpler approach. Where comparison was possible, the results of the two methods of analysis showed good agreement. The following parameters were evaluated: average relative reaction probabilities for H*–HI and H*–RD collisions (where the asterisk denotes the hot species), the fraction of H* moderated to that reacting hot in pure RD, and β, the average fractional energy loss by H* is collision with RD. The most important conclusions which can be drawn from the results are: (a) a simple...

An Ab initio study of the stability of the symmetrical and unsymmetrical difluoroethylenes relative to ethylene and monofluoroethylene

Ab initio calculations of the total molecular energy (ET), charge population, and dipole moments for ethylene, monofluoroethylene, cis- and trans-1,2-difluoroethylene, and 1,1-difluoroethylene have been carried out using a (7,3) basis set with full geometry optimization, and (7,3), (7,3,1), and (9,5) basis sets using recent experimental geometries. We confirm the finding of Kollman, who used partial geometry optimization at the STO-3G level and earlier experimental geometries, that 1,1-difluoroethylene is more stable than either of the 1,2-isomers, in accord with the behaviour of 1,1- and 1,2-disubstituted ethylenes in general as noted by Epiotis et al. The stability of the difluoroethylenes is examined in terms of ΔET, and where possible the corresponding reaction heat (ΔH00)zpe, for the disproportionation reaction difluoroethylene + ethylene → 2 monofluoroethylene. The closed shell molecular species CH2CH2 and CH2CHF are thus utilized as a composite molecular energy baseline to assess destabilization or stabilization effects, in contrast to the procedure followed by Epiotis et al. and by Whangbo et al. which involves open shell molecular fragments. This alternative approach, using the disproportionation reaction, leads to the conclusion that the slightly greater stability of the cis-relative to the trans-isomer, (ΔH00)zpe=+1.08 kcal mol–1, is due to lesser destabilization in the cis-isomer, since ΔET for both disproportionation reactions is substantially negative lying in the range –6 to –8 kcal mol–1.