Internuclear

Internuclear is an adjective used in chemistry and nuclear physics to describe phenomena, measurements, or interactions occurring between atomic nuclei. In chemistry, the term is most commonly encountered in reference to internuclear distance—the straight-line separation between the nuclei of two atoms within a molecule. Internuclear distance determines bond length, influences bond strength, and correlates with vibrational frequencies. In diatomic molecules, the equilibrium internuclear distance corresponds to the minimum of the potential energy curve; compressing or stretching the bond changes the energy and forces accordingly. Bond lengths vary with atom types and bond order; typical values include H–H about 74 picometers, C–C about 154 pm, and O=O about 120 pm. Spectroscopic and computational methods analyze how internuclear distance affects electronic structure and energy.

In nuclear physics, internuclear distance also appears as the separation between two nuclei during collisions or in composite systems, such as heavy-ion fusion or molecular dynamics simulations that include nuclei. The internuclear potential describes the interaction as a function of separation and is central to models such as the proximity potential or two-center shell models. Variations in internuclear distance influence tunneling probabilities, reaction cross sections, and the formation of compound nuclei.

The term is used alongside concepts such as internuclear axis and internuclear repulsion, referring to the line or forces along the line joining two nuclei. Etymologically, it derives from inter- + nuclear, indicating relations between nuclei rather than within a single nucleus.