  Mass spectrum of charmonium is computed in the framework of potential
non-relativistic quantum chromodynamics. \textit{O}$(1/m)$ and
\textit{O}$(1/m^2)$ relativistic corrections to the Cornell potential and
spin-dependent potential have been added, and is solved numerically. New
experimentally observed and modified positive and negative parity states like
${{\boldsymbol \psi}{(4230)}}$, ${{\boldsymbol \psi}{(4260)}}$, ${{\boldsymbol
\psi}{(4360)}}$, ${{\boldsymbol \psi}{(4390)}}$, ${{\boldsymbol
\psi}{(4660)}}$, ${{\boldsymbol \chi}_{{c1}}{(4140)}}$ and ${{\boldsymbol
\chi}_{{c1}}{(4274)}}$ near open-flavor threshold have also been studied. We
explain them as admixtures of S-D wave states and P-wave states. Apart from
these states, some other states like ${{\mathit X}{(3915)}}$, ${{\boldsymbol
\chi}_{{c1}}{(3872)}}$, ${{\boldsymbol \psi}{(3770)}}$ and ${{\boldsymbol
\psi}{(4160)}}$ have been identified as $2^3P_0$, $2^3P_1$, $1^3D_1$ and
$2^3D_1$ states. Subsequently, the electromagnetic transition widths and
$\gamma\gamma$, $e^+e^-$, light hadron and $\gamma\gamma\gamma$ decay widths of
several states are calculated at various leading orders. All the calculated
results are compared with experimental and results from various theoretical
models.
