30Si28Si

30Si28Si is an isotopologue of the silicon dimer Si2, consisting of one silicon-30 nucleus and one silicon-28 nucleus bonded together. It is one of several isotopologues formed when the two silicon atoms in Si2 have different isotopic compositions. In natural silicon, the most abundant isotope is 28Si, with smaller amounts of 29Si and 30Si; thus, 30Si28Si occurs with lower frequency than the all-28Si variant.

In terms of physical properties, 30Si28Si has a molecular mass close to the sum of the two constituent isotopes, about 57.95 amu, and its spectroscopic constants depend on the reduced mass of the pair. The reduced mass for 28Si-30Si is 14.4827 u, which shifts rotational and vibrational transition frequencies compared with the symmetric 28Si28Si isotopologue. The molecule is nonpolar, since the electronic structure remains symmetric with two identical nuclei in charge; isotope substitution affects only nuclear masses and thus the rovibrational spectrum, not the dipole moment.

Detection and use of 30Si28Si occur mainly in high-resolution laboratory spectroscopy and, where possible, in astronomical spectroscopy and combustion studies that examine isotopic effects. The relative abundance of 30Si28Si in natural samples is small, estimated by the combination of the natural abundances of 28Si and 30Si; nonetheless, it provides valuable data for testing molecular constants, isotopic shifts, and models of silicon-containing environments.

See also: 28Si28Si, 28Si29Si, 29Si29Si, 30Si30Si.