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

The spectroscopy and photodissociation dynamics of the NCN radical have bee n investigated by fast beam photofragment translational spectroscopy. The ( B) over tilde (3)Sigma(u)(-)<-- (X) over tilde (3)Sigma(g)(-), (c) over til de (1)Pi(u)<--(a) over tilde (1)Delta(g), and (d) over tilde (1)Delta(u)<-- (a) over tilde (1)Delta(g) transitions were examined. The major dissociatio n products for the (B) over tilde (3)Sigma(u)(-) and (c) over tilde (1)Pi(u ) states are N-2((X) over tilde (1)Sigma(g)(+))+C(P-3), while the (d) over tilde (1)Delta(u) state dissociates to N-2((X) over tilde (1)Sigma(g)(+))+C (D-1). The dissociation channel, N(S-4)+CN((X) over tilde (2)Sigma(+)) is o bserved for the (B) over tilde (3)Sigma(u)(-) state at photon energies grea ter than 4.9 eV, where it comprises approximate to 25 +/- 10% of the total signal. At all photon energies, the photofragment translational energy dist ributions show a resolved progression corresponding to the vibrational exci tation of the N-2 photofragment. The rotational distributions of the molecu lar fragments suggest that the dissociation pathway for the N-2 loss channe l involves a bent transition state while the N+CN photofragments are produc ed via a linear dissociation mechanism. The P(E-T) distributions provide bo nd dissociation energies of 2.54 +/- 0.030 and 4.56 +/- 0.040 eV for the N- 2 and CN loss channels, respectively, yielding Delta H-f,H-0 K(NCN)=4.83 +/ - 0.030 eV. (C) 1999 American Institute of Physics. [S0021-9606(99)00535-8] .