86Sr2

86Sr2 refers to the doubly ionized isotope of the element strontium with mass number 86. Strontium (Sr) is element 38, and 86Sr contains 38 protons and 48 neutrons. It is one of the stable isotopes of strontium, part of the quartet 84Sr, 86Sr, 87Sr, and 88Sr, and it accounts for roughly 10 percent of natural strontium.

In ionic form, 86Sr2+ represents strontium that has lost two electrons. The two 5s electrons are removed to form the Sr2+ ion, whose electronic configuration is equivalent to that of krypton (Kr). The first and second ionization energies of strontium are about 5.7 eV and 11 eV, respectively, with small differences among isotopes.

Natural abundance of 86Sr makes it useful in geochemical and cosmochemical studies that rely on Sr isotope ratios. In mass spectrometry and isotope ratio analysis, 86Sr is measured alongside other stable strontium isotopes (notably 87Sr and 88Sr) to determine the 86Sr/88Sr ratio, which informs investigations of planetary differentiation, dating, and sedimentary processes. The 87Sr/86Sr ratio is particularly important in rubidium-strontium dating, a radiometric method used in geology and archaeology.

In practical terms, 86Sr2+ can appear in plasma or combustion sources used for mass spectrometry, producing a peak at a characteristic mass-to-charge ratio (m/z) corresponding to m/z ≈ 43 for the Sr2+ ion. While isotopic differences are small, high-precision instruments can detect and quantify 86Sr relative to other isotopes.

See also: strontium, isotopes of strontium, isotope ratio mass spectrometry, rubidium-strontium dating.