Photodissociation dynamics of the CNN free radical

Abstract

The spectroscopy and photodissociation dynamics of the à 3Π and B̃ 3Σ− states of the CNN radical have been investigated by fast beam photofragment translational spectroscopy. Vibronic transitions located more than 1000 cm−1 above the à 3Π←X̃ 3Σ− origin were found to predissociate. Photofragment yield spectra for the B̃ 3Σ−←X̃ 3Σ− band between 40 800 and 45 460 cm−1 display resolved vibrational progressions with peak spacing of ≈1000 cm−1 corresponding to symmetric stretch 10n and combination band 10n301 progressions. Ground state products C(3P)+N2 were found to be the major photodissociation channel for both the à 3Π and B̃ 3Σ− states. The translational energy distributions for the à 3Π state are bimodal with high and low translational energy components. The distributions for the B̃ 3Σ− state reveal partially resolved vibrational structure for the N2 photofragment and indicate extensive vibrational and rotational excitation of this fragment. These results suggest that bent geometries are involved in the dissociation mechanism and provide more accurate values: ΔfH0(CNN)=6.16±0.05 eV and ΔfH298(CNN)=6.15±0.05 eV. These values, coupled with recent D0(RH) and D298(RH) values from Clifford et al. [J. Phys. Chem. 102, 7100 (1998)], yield ΔfH0(HCNN)=5.02±0.18 eV, ΔfH298(HCNN)=4.98±0.18 eV, ΔfH0(H2CNN)=3.09±0.21 eV, and ΔfH0(H2CNN)=3.09±0.21 eV.