Optical emission spectroscopy diagnostic of carbon plasma created by an excimer KrF laser pulse at three different laser fluences (12, 25 and 32 J/cm(2)) is performed under nitrogen ambience at a pressure of 1 mbar. A spatio-temporal evolution study of different species such as CII, CI, NII, C-2 and CN is presented and comparisons between them are made. We found that C2 and CN emission intensity did not depend on laser fluence while CII and NII emission intensity increases continuously with the raise of the fluence. The spatio-temporal evolution of CN follows the C-2 one at the vicinity of the target surface, whereas for greater distances, it follows the CII one. A scenario of CN formation is thus proposed, by stating that at the neighbourhood of the target surface CN molecules comes directly from this surface or from the bimolecular reaction between C-2 and N-2 in the gas phase. However, at greater distances, CN molecules are mainly produced by a three-body reaction between the atomic species C and N. (c) 2005 Elsevier B.V. All rights reserved.