Thermochemistry of Gaseous OSiI, OSiI_2, SiI, and SiI-2

摘要

Gaseous reaction equilibria in the Si-O-I system were investigated by mass spectrometry, leading to identification and thermochemical characterization of the species OSiI, OSiI2. SiI, and Sill. Species were generated by the addition of gaseous 12 to an effusion cell reactor containing a Si/SiO2 mixture of composition "SiO". Equilibria involving the Si-O-I species were measured in the range 1350 to 1540 K. From third law analysis, the enthalpies of formation ofOSiI, OSiI2, SiI, and Sill were derived as >= - 21,7 (+-) 5, >+ -74,5 (+-) 5,61.0 (+-)2, and 21.6 (+-) 3.3kcalmol-l,respectively. Although the values for SiI and SiI~ are in good agreement with selected values in a recent compilation, the results for OSiI and OSiI_2 are 25-30 kcal mol-l less stable than semiempirical estimates developed for modeling of metal halide lamp chemistry .In some instances, other estimated th'ermoche~caldat~base val,ues differ substantially from both theoretical and experimental results; reasons for these dIscrepancIes are dlsCussed.