Knowledge Bank

Electronically excited levels in the NCO free radical have been probed using laser fluorescence excitation, in order to observe higher vibronic levels of the $A~2\Sigma +$ state and to locate the onset of predissociation. Spectra have been recorded over the wave number range 27 400 - $32900cm-1$, from the $A~(0,0,2)2\Sigma +\leftarrow X~(0,0,0)2\Pi$ band up through the $B~(1,0,0)2\Pi \leftarrow X~(0,0,0)2\Pi$ band. Vibrational assignments have been made for a number of newly observed $A~(0,0,2)2\Sigma +\leftarrow X~(0,0,0)2\Pi$ bands, and the band origin wave numbers and upper level rotational constants have been derived by comparison of spectra with simulations. Decay lifetime have been measured for a large number of both assigned and unassigned excited vibronic levels. The onset of predissociation appears to occur at energies slightly below that of the $B~(0,0,0)$ level, at $31750cm-1$. These data also suggest that predissociation occurs at lower energies in bent geometries that in a linear configuration.