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 Å. 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 C_2v point group. The CCO molecular skeleton is presumed to be in-plane bent in both these excited states (point group C_s). 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.