4d0

4d0 is a shorthand notation used in atomic chemistry and solid-state physics to indicate that the 4d subshell contains zero electrons. It denotes the occupancy of the 4d orbitals in an atom, ion, or a calculated electronic state, and is part of the broader d-subshell notation that ranges from 0 to 10 electrons.

In electron configurations, the superscript after the subshell specifies the number of electrons occupying that subshell. A 4d0 configuration occurs in highly oxidized states of elements in the 4d transition-metal series (the Y–Cd region) or in other ions where the 4d electrons have been removed. For example, Nb5+, Mo6+, Zr4+, and Y3+ ions can be described as having a 4d0 configuration.

Because there are no electrons in the 4d subshell, transitions within 4d-d levels are absent for 4d0 ions. Spectroscopic features involving the 4d set arise from excitations into the 4d orbitals from other shells or from ligand-to-metal charge transfer in compounds. In crystal-field and ligand-field theories, a d0 configuration is often a reference state for analyzing other oxidation or spin states.

4d0 states are encountered in a variety of chemical contexts, including oxoanions and oxometalates of high oxidation state, and in spectroscopic studies of transition-metal ions. They serve as a baseline for comparing partially filled 4d configurations and their electronic structure.

See also: electron configuration; d-block elements; transition metals; d0 configuration.