Mass spectrum of charmonium is computed in the framework of potential non-relativistic quantum chromodynamics. O(1/m) and 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 ψ(4230), ψ(4260), ψ(4360), ψ(4390), ψ(4660), χ c1 (4140) and χ 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 X(3915), χ c1 (3872), ψ(3770) and ψ(4160) have been identified as 2 3 P 0 , 2 3 P 1 , 1 3 D 1 and 2 3 D 1 states. Subsequently, the electromagnetic transition widths and γγ, e + e − , light hadron and γγγ 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.