Totally 3045 transitions into the 2(3)Pi(g) v = 0-42, J = 0-103, Omega = 0, 1, 2 rovibrational levels have been observed by infrared-infrared double resonance fluorescence excitation and two-photon spectroscopy. Molecular constants including the spin-orbit interaction parameters are obtained. Although the K-2 2(3)Pi(g) state dissociates to the 4s + 3d atomic limit, it is strongly mixed with the P-3 ionic states in the range of the potential well. This mixing results in a relatively large equilibrium internuclear distance R-e = 5.254 angstrom and a larger spin-orbit constant angstrom(0) similar to 14.17 cm(-1) than that of the atomic limit -2.33 cm(-1). Strong perturbations of the 2(3)Pi(g) levels observed are attributed to the spin-orbit coupling with the 4(1)Sigma(+)(g) state.