The effect of delay time on the CO and CH3 radicals resulting from the photolysis of acetone by 193 nm excimer laser

A time-resolved Fourier transform IR spectrometer is used to measure the emitted spectra of the fragments resulting from the photodissociation of 3S Rydberg state acetone by a 193 nm excimer laser at different delay times between the FTIR and the laser. Two vibrational bands are detected. The first band, a single peak in the range of 3200–2750 cm−1, is assigned to be the CH of the methyl radicals, is unresolved. The second is a resolved double peak band in the range of 2250–1950 cm−1 is assigned to be the P and R branches of the CO molecule. The emitted spectra of the CO molecule and the methyl radicals are measured at different delay times from 1 to 50 μs. The integrated intensity of the emitted spectra of CO was found to increase with delay times up to 50 μs, while that of the methyl radicals showed the opposite behaviour. Plotting the relationship between the laser power and the integrated intensity of the CO spectrum yielded a straight line with a gradient ∼1. this may indicate that the process is a single-photon reaction.