Absorption spectrum of ketene in the visible and near ultra-violet

Abstract

The absorption spectrum of ketene in the visible and near ultra-violet has been studied with absorption paths of up to 24 m atm. Diffuse bands extend to a long wavelength limit of 4735 A. The mean spacing between successive bands changes from 365±50 cm–1 at higher frequencies to 475±20 cm–1 at frequencies lower than 26000 cm–1, indicating the presence of two electronic transitions. SCF–MO calculations of the π-electronic structure of ketene in the Pariser-Parr-Pople approximation confirm the assignment of these two absorptions to transitions to the two lowest excited states, which correlate with 1A2 and 3A2 states in the C2v point group. The CCO molecular skeleton is presumed to be in-plane bent in both these excited states (point group Cs). The diffuse nature of the bands is attributed to predissociation, setting an upper limit of 61 kcal/mole for the lowest dissociation energy of ketene.