CO₂ laser‐induced decomposition of ethanol

Abstract

The multiple photon absorption and decomposition of ethanol irradiated by pulsed 9P 18 infrared radiation (1048.7 cm-') from a TEA GO2 laser has been studied in the fluence range 1.5 to 5 J cm-2. The absorption cross-section is pressure-dependent due to rapid collisional rotational hole-filling. At low pressures the only important decomposition channel following absorption is molecular dehydration of ethanol to yield ethene, but at higher pressures hydrogen, methane, carbon monoxide, ethane, and ethyne are also produced. In the irradiation of pure ethanol under 'collision-free' conditions, thermal decomposition following collisional redistribution of energy makes only a small contribution to the overall decomposition yield at fluences above 3.5 J cm-' but may become more significant at lower fluences. Modelling using RRKM calculations has been employed to link measured absorbed energies to extents of decomposition of ethanol. Both these calculations and the absorption measurements indicate that at low pressures only a fraction of the irradiated ethanol molecules absorb the 9P18 radiation. 0

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