The use of isotopic substitution and matrix isolation techniques in determining molecular constants for group IVA tetrahalides

Improved values of molecular constants of group IVA tetrahalides are reported. Accurate frequencies, including those of different isotopically substituted species, have been determined using matrix isolation spectroscopy in conjunction with isotope techniques (for SiF₄, GeF₄, SiCl₄, Si³⁵Cl₄, SiBr₄, GeBr₄, ⁷⁴GeBr₄, ^70/76GeBr₄, SnBr₄, ¹¹⁶SnBr₄ and ¹²⁴SnBr₄) and from vapour -phase IR spectra (for SiF₄, GeF₄, ⁷⁴GeF₄, SiCl₄, Si³⁵Cl₄ SiBr₄, GeBr₄, ⁷⁴GeBr₄, SnBr₄, ¹¹⁶SnBr₄ and ¹²⁴SnBr₄). Band contour analyses, often rendered difficult by isotopic effects and hot-band progressions, were simplified by measuring the spectra of isotopically pure compounds (e.g. ⁷⁴GeF₄, ¹¹⁶Sn³⁵Cl₄) and by measurements at lower temperatures (SiF)₄. The isotopic shifts, Coriolis coupling and force constant values determined in this study are more accurate than those previously reported for some of the molecules. In addition to the presentation of new data the known spectral information concerning the other tetrahalides of silicon, germanium and tin are reviewed.