Photodissociation dynamics of the singlet and triplet states of the NCN radical

The spectroscopy and photodissociation dynamics of the NCN radical have been investigated by fast beam photofragment translational spectroscopy. The B̃ 3Σu−←X̃ 3Σg−, c̃ 1Πu←ã 1Δg, and d̃ 1Δu←ã 1Δg transitions were examined. The major dissociation products for the B̃ 3Σu− and c̃ 1Πu states are N2(X̃ 1Σg+)+C(3P), while the d̃ 1Δu state dissociates to N2(X̃ 1Σg+)+C(1D). The dissociation channel, N(4S)+CN(X̃ 2Σ+) is observed for the B̃ 3Σu− state at photon energies greater than 4.9 eV, where it comprises ≈25±10% of the total signal. At all photon energies, the photofragment translational energy distributions show a resolved progression corresponding to the vibrational excitation of the N2 photofragment. The rotational distributions of the molecular fragments suggest that the dissociation pathway for the N2 loss channel involves a bent transition state while the N+CN photofragments are produced via a linear dissociation mechanism. The P(ET) distributions provide bond dissociation energies of 2.54±0.030 and 4.56±0.040 eV for the N2 and CN loss channels, respectively, yielding ΔHf,0 K(NCN)=4.83±0.030 eV.