**Abstract**

We have investigated the ground state and the two lowest excited
states of the CeF molecule using four-component relativistic
multiconfigurational quasidegenerate perturbation theory calculations,
assuming the reduced frozen-core approximation. The ground state is
found to be
(4*f*^{1})(5*d*^{1})(6*s*^{1}),
with Ω = 3.5, where Ω is the total electronic angular
momentum around the molecular axis. The lowest excited state with
Ω = 4.5 is calculated to be 0.104 eV above the ground state and
corresponds to the state experimentally found at 0.087 eV. The second
lowest excited state is experimentally found at 0.186 eV above the
ground state, with Ω = 3.5 based on ligand field theory
calculations. The corresponding state having Ω = 3.5 is
calculated to be 0.314 eV above the ground state. Around this state,
we also have the state with Ω = 4.5. The spectroscopic
constants *R*_{e}, ω_{e}, and
*ν*(1–0) calculated for the ground and first excited states are
in almost perfect agreement with the experimental values. The
characteristics of the CeF ground state are discussed, making
comparison with the LaF^{+} and LaF molecules. We denote the
*d*- and *f*-like polarization functions as *d** and
*f**. The chemical bond of CeF is constructed via
{Ce^{3.6+}(5*p*^{6}*d**^{0.3}*f**^{0.1})F^{0.6−}(2*p*^{5.6})}^{3+}
formation, which causes the three valence electrons to be localized at
Ce^{3.6+}.