Evidence for CN in spectroscopic studies of laser-induced plasma during pulsed irradiation of graphite targets in nitrogen and ammonia

Mass-and time-integrated optical emission spectra were recorded during direct XeCl laser ablation (308 nm, 30 ns) of graphite targets in N-2 and in NH3 atmospheres at various pressures (10(-2)-250 Pa) and at different laser fluences (3, 6, 12 J cm(-2)). Spectra in vacuo (10(-4) Pa) were also acquired. The optical emission spectra of the laser-induced plasma are characterized by strong molecular emission bands of C-2 and CN and by lines of atomic ions (C+, N+). At the highest pressures the spectra are dominated by a C-2 Swan system (vibrational sequences Delta nu = -2, -1, 0, +1, +2) and a CN violet system (Delta nu = -1, 0, +1). Their intensities increase with an increase of gas pressure. Mass spectrometry was also performed on the ablated materials and various chemical species were found; the most common ones were C, CN and C2N2.