35Cl

35Cl is the stable isotope of chlorine with a mass number of 35. It is one of the two stable chlorine isotopes, the other being 37Cl. In nature, about 75.8% of chlorine atoms are 35Cl and about 24.2% are 37Cl, giving a natural 35Cl/37Cl ratio of roughly 3:1. The atomic mass of 35Cl is 34.968853 u, while 37Cl has an atomic mass of 36.965903 u.

Nuclear properties of 35Cl include a nuclear spin of I = 3/2, making it a quadrupolar nucleus. Both 35Cl and 37Cl are stable and exhibit no radioactive decay under ordinary conditions. The isotopic composition of chlorine in natural samples can vary slightly due to geological, biological, and chemical processes, a feature used in isotope geochemistry and archaeology to provenance materials and study transport processes.

In mass spectrometry, chlorine’s two stable isotopes produce characteristic patterns. For molecules containing one chlorine atom, the molecular ion usually appears as a pair of peaks (M and M+2) whose relative intensities reflect the natural abundances of 35Cl and 37Cl; the M peak is typically about three times as intense as the M+2 peak. This isotopic pattern is a common diagnostic feature in chlorine-containing compounds.

Applications of 35Cl include its use as a stable isotope tracer in chemistry and geoscience, as well as in mass spectrometry for internal standardization and compound characterization. Because both chlorine isotopes are stable, 35Cl is not a source of radiogenic fallout but provides valuable isotopic and spectrometric information in various disciplines.