The decomposition of ethanol vapour by infrared radiation from a pulsed HF-laser

The decomposition of ethanol vapour induced by infrared radiation from a pulsed HF-laser has been studied as a function of pressure. At high pressures, above 10 torr, the main primary processes appear to be:C₂H₅OH → H₂ + CH₃CHO,C₂H₅OH → C₂H₄ + H₂O,C₂H₅OH → CH₃ + CH₂OHin a ratio of 3:2:1 which is independent of pressure. At low pressures the process yielding C₂H₄ and H₂O becomes dominant. The results suggest that the high pressure behaviour involves a “thermal” decomposition with collisional processes dominating, whereas at low pressures the decomposition is due to multiple photon absorption which at the lowest pressures approaches a collision-free unimolecular decomposition.