28Si29Si
28Si29Si refers to a molecular species composed of one atom of silicon-28 and one atom of silicon-29. Silicon isotopes are distinguished by the number of neutrons in their nucleus. Silicon has three stable isotopes: silicon-28 (28Si), silicon-29 (29Si), and silicon-30 (30Si). Silicon-28 is by far the most abundant, making up approximately 92.2% of natural silicon. Silicon-29 accounts for about 4.7%, and silicon-30 constitutes around 3.1%.
The molecule 28Si29Si would therefore be a heteronuclear diatomic molecule of silicon. Such molecules are typically