Photoionization Study of the Singlets [1s22p(2p3/2)ns 1p, 1s22p (2p)nd 1p, 1s22p (2p1/2)np 1p, 1s22p (2p3/2)np 1d] and Triplets [1s22p (2po)ns 3p0,1,2 ] Rydberg Series for the Niv Ions Via the Modified Atomic Orbital Theory