THE RATES OF HCL LOSS FROM ENERGY-SELECTED ETHYLCHLORIDE IONS - A CASE OF TUNNELING THROUGH AN H-ATOM TRANSFER BARRIER

被引:40
作者
BOOZE, JA
WEITZEL, KM
BAER, T
机构
[1] Department of Chemistry, University of North Carolina, Chapel Hill
关键词
D O I
10.1063/1.459736
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The dissociation rates of energy-selected ethylchloride and deuterated ethylchloride ions were measured as a function of the parent-ion internal energy by the method of photoelectron photoion coincidence. Previously performed ab initio calculations indicated that the rate-determining step for this reaction is an H-atom transfer from the beta carbon to the Cl atom via a substantial energy barrier of 92 kJ/mol (referenced to the zero-point energy). The ion internal energy range in which the experimental rates varied between 10(5) and 10(7) s-1 was found to lie well below the calculated barrier for H-atom transfer. The rates were modeled with the Rice-Ramsperger-Kassel-Marcus statistical theory which includes a tunneling step through an Eckart potential. The vibrational frequencies of both the normal and deuterated ethylchloride ions were determined by ab initio molecular-orbital methods. The theory accounted very well for the absolute rates including the strong deuterium isotope effect. The measured kinetic-energy release distribution appears nonstatistical. This indicates that the ion-dipole complex, which lies in between the transition state and the C2H4+ + HCl products, is ineffective in randomizing the excess energy among the product degrees of freedom.
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页码:3649 / 3656
页数:8
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