The NbN C-3 Pi-X-3 Delta (1-0) band is studied in the free jet setup. The spin-orbit interaction between v =1 of (3)Pi(1) and e(1)Pi states destroyed the symmetric splitting of C-3 Pi substates. Unusually high 685 cm(-1) spin orbit interaction matrix element between them pushed the (3)Pi(1) substate below (3)Pi(0) component. Our ab initio calculations estimate (3)Pi(2) - (3)Pi(0) separation 414 cm(-1), which is in an excellent agreement with the observed value 404 cm-1, and places the (3)Pi(1) state 244 cm(-1) below (3)Pi(0) state, in somewhat poor agreement with the experimental separation of 449 cm(-1). This error is primarily due to the error in our calculated unperturbed (3)Pi(1)- (1)Pi energy separation. (C) 2016 Elsevier B.V. All rights reserved.