Photodissociation dynamics of the CNN free radical

The spectroscopy and photodissociation dynamics of the (A) over tilde (3)Pi and (B) over tilde (3)Sigma(-) states of the CNN radical have been investi gated by fast beam photofragment translational spectroscopy. Vibronic trans itions located more than 1000 cm(-1) above the (A) over tilde (3)Pi<--(X) o ver tilde (3)Sigma(-) origin were found to predissociate. Photofragment yie ld spectra for the (B) over tilde (3)Sigma(-)<--(X) over tilde (3)Sigma(-) band between 40 800 and 45 460 cm(-1) display resolved vibrational progress ions with peak spacing of approximate to 1000 cm(-1) corresponding to symme tric stretch 1(0)(n) and combination band 1(0)(n)3(0)(1) progressions. Grou nd state products C(P-3)+N-2 were found to be the major photodissociation c hannel for both the (A) over tilde (3)Pi and (B) over tilde (3)Sigma(-) sta tes. The translational energy distributions for the (A) over tilde (3)Pi st ate are bimodal with high and low translational energy components. The dist ributions for the (B) over tilde (3)Sigma(-) state reveal partially resolve d vibrational structure for the N-2 photofragment and indicate extensive vi brational and rotational excitation of this fragment. These results suggest that bent geometries are involved in the dissociation mechanism and provid e more accurate values: Delta(f)H(0)(CNN)=6.16 +/- 0.05 eV and Delta(f)H(29 8)(CNN)=6.15 +/- 0.05 eV. These values, coupled with recent D-0(RH) and D-2 98(RH) values from Clifford [J. Phys. Chem. 102, 7100 (1998)], yield Delta( f)H(0)(HCNN)=5.02 +/- 0.18 eV, Delta(f)H(298)(HCNN)=4.98 +/- 0.18 eV, Delta (f)H(0)(H2CNN)=3.09 +/- 0.21 eV, and Delta(f)H(0)(H2CNN)=3.09 +/- 0.21 eV. (C) 2000 American Institute of Physics. [S0021-9606(00)01334-9].