A theoretical study of electronic spectra in the linear cationic chains NC2n+1N+ (n = 1-6)

► ► The NC2n+1N+ chains are more susceptible to fragmentation than NC2nN+ clusters. ► The BLA character of X2Пg/u is more evident than corresponding 12Пu/g excited state. ► CASPT2 method can give reliable results for vertical transition energy calculations. ► The nonlinear λ -n relationship has been found in NC2n+1N+ (n = 1-6). The 22Пu/g ← X2Пg/u transition may be detected more easily in the further experiments.