  In this work we calculate the mass spectrum of charmonium for $1P,...,3P$
states of $0^{++}$ , $1^{++}$, as well as for $1S,...,4S$ states of $0^{-+}$,
and $1S, ...,5D$ states of $1^{--}$ along with the two-photon decay widths of
ground and first excited state of $0^{++}$ quarkonia for the process,
$O^{++}\rightarrow \gamma\gamma$ in the framework of a QCD motivated
Bethe-Salpeter Equation. In this $4\times 4$ BSE framework, the coupled
Salpeter equations are first shown to decouple for the confining part of
interaction, under heavy-quark approximation, and analyically solved, and later
the one-gluon-exchange interaction is perturbatively incorporated leading to
mass spectral equations for various quarkonia. The analytic forms of wave
functions obtained are used for calculation of two-photon decay widths of
$\chi_{c0}$. Our results are in reasonable agreement with data (where ever
available) and other models.
