  Electronic properties of V$_2$OPO$_4$ have been investigated by means of hard
x-ray photoemission spectroscopy (HAXPES) and subsequent theoretical
calculations. The V 1$s$ and 2$p$ HAXPES spectra are consistent with the charge
ordering of V$^{2+}$ and V$^{3+}$. The binding energy difference between the
V$^{2+}$ and V$^{3+}$ components is unexpectedly large indicating large
bonding-antibonding splitting between them in the final states of core level
photoemission. The V 1$s$ HAXPES spectrum exhibits a charge transfer satellite
which can be analyzed by configuration interaction calculations on a V$_2$O$_9$
cluster. The V 3$d$ spectral weight near the Fermi level is assigned to the
3$d$ $t_{2g}$ orbitals of the V$^{2+}$ site. The broad V 3$d$ spectral
distribution is consistent with the strong hybridization between V$^{2+}$ and
V$^{3+}$ in the ground state. The core level and valence band HAXPES results
indicate substantial charge transfer from the V$^{2+}$ site to the V$^{3+}$
site.7 figure
