KINETIC AND THERMOCHEMICAL STUDY OF THE SIH3 + HBR REVERSIBLE SIH4 + BR AND SIH3 + HI REVERSIBLE SIH4 + I EQUILIBRIA

被引:90
作者
SEETULA, JA
FENG, Y
GUTMAN, D
SEAKINS, PW
PILLING, MJ
机构
[1] CATHOLIC UNIV AMER,DEPT CHEM,WASHINGTON,DC 20064
[2] UNIV OXFORD,PHYS CHEM LAB,OXFORD OX1 3QZ,ENGLAND
关键词
D O I
10.1021/j100157a030
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 reactions between SiH3 and HI (2) and SiH3 and HBr (5) have been studied by excimer laser flash photolysis coupled with photoionization mass spectrometry over the temperature range 295-550 K, giving k2 = 7.3 (+/- 2.8) X 10(-12) exp{2.0 (+/- 1.4) kJ mol-1/RT} and k5 = 1.2 (+/- 0.4) X 10(-12) exp{0.7 (+/- 1.2) kJ mol-1/RT} cm3 molecule-1 s-1. The reverse of reaction 5 was also studied by using excimer laser flash photolysis/resonance fluorescence over the temperature range 298-483 K, giving k-5 = 1.6 (+/- 0.6) X 10(-10) exp{-18.0 (+/- 1.3) kJ mol-1/RT} cm3 molecule-1 s-1. The enthalpy change for reaction 5, DELTA-H-degrees-298, was calculated from k5(T)/k-5(T) using second law {-18.4 (+/- 1.8) kJ mol-1} and third law {-17.4 (+/- 1.6) kJ mol-1} techniques, and these values were then employed to provide a recommended value for DELTA-H-degrees-f,298 for SiH3 of 200.5 (+/- 2.5) kJ mol-1. The SiH3-H bond enthalpy at 298 K was also determined, 384.1 (+/- 2.0) kJ mol-1. The determinations of k2(T) were combined with literature values of k-2(T) in an additional third law determination of the SiH3 heat of formation. The result, DELTA-H-degrees-f,298 = 200.8 (+/- 3.4) kJ mol-1, is of reduced accuracy but in complete accord with the recommended value based on the study of reaction 5. The latter determination also provides a reconciliation of formerly disparate literature values for this heat of formation. The reactivity of SiH3 is compared to that of the alkyl radicals with both HI and HBr.
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页码:1658 / 1664
页数:7
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