CW-cavity ring down spectroscopy was used to record the spectrum of (C2H2)-C-12-N-2 in a free jet expansion around the 2CH acetylene band. Twenty lines were assigned thanks to combination differences, which were combined with literature values leading to the retrieval of ground state rotational constants consistent for a broader set of J ''. Effective rotational constants, the band origin and the estimation of the lifetime of the perturbed upper state are determined. (C) 2012 Elsevier B. V. All rights reserved.