Molecular ion

An ion formed simply by the removal from (positive ions) or addition to (negative ions) a molecule of one or more electrons. For molecules containing multi-isotope elements, a number of different isotopologue ions will be formed, but the term molecular ion is restricted to the ion formed by the most abundant naturally occurring isotopes of all atoms that make up the molecule. For instance, electron ionization of BF₃ gives two isotopologue ions, ¹⁰B¹⁹F₃^+. of m/z 67 and ¹¹B¹⁹F₃^+. of m/z 68, the heavier one being the molecular ion since ¹¹B is more abundant than ¹⁰B. The lighter ion is sometimes termed an isotopic molecular ion. The mass of the molecular ion should therefore be calculated by the sum of the masses of the most abundant naturally occuring isotopes of all its atoms with a correction for the masses of the electron(s) that were added or removed.

Related Terms

Isotopologue Ion Isotopic Molecular Ion Base Isotope Cluster Ion