Application of the Thermal Lens Technique to Infrared Multiple Photon Photochemistry. Estimation of Transient Temperatures in Cyclobutanone

Article abstract of DOI:10.1021/j100409a013

The thermal lens technique is applied to infrared multiple photon photochemistry of cyclobutanone at pressures from 1 to 10 Torr, where energy transfer is competitive with the rate of vibrational excitation by absorption of radiation from a pulsed CO2 laser beam.Thermal lens signals consisting of rapid (microsecond time scale) oscillations of transmitted HeNe probe laser intensity are attributed to density fluctuations caused by expansion waves that propagate radially toward the center from the outside surface of the laser heated volume, where radially outward propagating shock waves also originate.Gas temperature is estimated from the time delay between the CO2 laser pulse and the onset of oscillations.Vibrational temperatures are estimated from the ethylene to cyclopropane product ratio obtained in cyclobutanone photolysis.