Large basis set SCFndash;CI calculations have been employed to determine the structures, inversion barriers, and inversion frequencies of SiH3, PH3+, and SH3++. All three species are nonplanar; however, the general trend is toward planarity as the positive charge increases. Values of the inversion barriers are 4.4 kcal/mol (SiH3), 2.9 kcal/mol (PH3+), and 0.5 kcal/mol (SH3++). Calculated frequencies of the vibrational transitions of the ngr;2modes of these molecules are consistent with experiment for PH3+, but not for SiH3.
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