The electronic structures, chemical bonds and stabilities of
${\rm{Ta}}_4{\rm{C}}_n^{-/0} $
(
n= 0–4) clusters are investigated by combining anion photoelectron spectroscopy with theoretical calculations. The vertical detachment energy values of
${\rm{Ta}}_4{\rm{C}}_n^{-} $
(
n= 0–4) anions are measured to be (1.16 ± 0.08), (1.35 ± 0.08), (1.51 ± 0.08), (1.30 ± 0.08), and (1.86 ± 0.08) eV, and the electron affinities of neutral Ta
4C
n(
n= 0–4) are estimated to be (1.10 ± 0.08), (1.31 ± 0.08), (1.44 ± 0.08), (1.21 ± 0.08), and (1.80 ± 0.08) eV, respectively. It is found that the geometry structure of
${\rm{Ta}}_4^- $
cluster is a tetrahedron, and the most stable structure of
${\rm{Ta}}_4{\rm{C}}_1^{-} $
has a carbon atom capping one face of the
${\rm{Ta}}_4^- $
tetrahedron, while in the ground state structure of
${\rm{Ta}}_4{\rm{C}}_2^{-} $
cluster, two carbon atoms cap two faces of the
${\rm{Ta}}_4^- $
tetrahedron, respectively. The lowest-lying isomer of
${\rm{Ta}}_4{\rm{C}}_3^{-} $
cluster holds a cube-cutting-angle structure. The ground state structure of
${\rm{Ta}}_4{\rm{C}}_4^{-} $
is a 2 × 2 × 2 cube. The neutral Ta
4C
n(
n= 0–4) clusters have similar structures to their anionic counterparts and the neutral Ta
4C
4cluster can be considered as the smallest cell for
α-TaC face-centered cube crystal. The analyses of molecular orbitals reveal that the SOMO of
${\rm{Ta}}_4{\rm{C}}_3^{-} $
is mainly localized on one tantalum atom, inducing a low VDE. Our results show that the Ta-Ta metal bonds are replaced by Ta-C covalent bonds gradually as the number of carbon atoms increases in
${\rm{Ta}}_4{\rm{C}}_n^{-/0} $
(
n= 0–4) clusters. The per-atom binding energy values of
${\rm{Ta}}_4{\rm{C}}_n^{-/0} $
(
n= 0–4) clusters are higher than those of
${\rm{Ta}}_{4+n}^{-/0} $
(
n= 0–4) clusters, indicating that the formation of Ta-C covalent bonds may raise the melting point. The per-atom binding energy of neutral Ta
4C
4is about 7.13 eV, which is quite high, which may contribute to the high melting point of
α-TaC as an ultra-high temperature ceramic material.
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