State-resolved translation energy distributions for NCO photodissociation

Abstract

The photodissociation dynamics of NCO have been examined using fast beam photofragment translational spectroscopy. Excitation of the 102, 301, and 102302 transitions of the B̃ 2Π←X̃ 2Π band produces N(4S)+CO photofragments exclusively, while excitation of the 103303 transition yields primarily N(2D)+CO photoproducts. The translational energy [P(ET)] distributions yield D0(N–CO)=2.34±0.03 eV, and ΔHf,00(NCO)=1.36±0.03 eV. The P(ET) distributions exhibit vibrationally resolved structure reflecting the vibrational and rotational distributions of the CO product. The N(2D)+CO distribution can be fit by phase space theory (PST), while the higher degree of CO rotational excitation for N(4S)+CO products implies that NCO passes through a bent geometry upon dissociation. The P(ET) distributions suggest that when the B̃ 2Π←X̃ 2Π band is excited, NCO undergoes internal conversion to its ground electronic state prior to dissociation. Excitation of NCO at 193 nm clearly leads to the production of N(2D)+CO fragments. While conclusive evidence for the higher energy O(3P)+CN(X 2Σ+) channel was not observed, the presence of this dissociation pathway could not be excluded.