The absorption of pulsed infrared radiation by cyclobutanone and its subsequent decomposition

The absorption characteristics of cyclobutanone vapour irradiated with a pulsed CO₂ TEA laser at fluences of 0.5–1.5 J cm⁻²have been studied over the pressure range 0.3 to 20 Torr using both joulemeter and opto-acoustic measurements of the absorbed energy. Under these conditions the product concentration for the two subsequent decomposition channels into ethene + ketene and cyclopropane + CO were determined. Above ≈ 3 Torr the results are consistent with a thermally equilibrated system whereas at lower pressures a distinct enhancement of the lower energy pathway to ethene occurs, indicative of a non-Boltzmann energy distribution.