Laser-Induced Photochemical Reactions of Methanol,Ethanol,1-Propanol,and 2-Propanol

This study focuses on the carbon dioxide laser-induced excitation and resultant dissociation of several members of a group of carbon-oxygen (C-O)-containing molecules, the alcohols methanol, ethanol, 1-propanol, and 2-propanol. The tunable continuous-wave infrared (cw) laser provides the energy of activation necessary for dissociation to occur after absorption into the C-O stretching fundamentals of the alcohols. Chemical reactions were monitored with the use of Fourier transform infrared spectroscopy, also used for identification of end products. After irradiation, ethanol and 1-propanol each yielded acetaldehyde. The products of the dissocation of methanol were carbon monoxide, formaldehyde, and hydrogen. The formaldehyde then reacted with excess methanol to produce methoxymethanol. Fourier transform interferograms were collected at specific time intervals, thus monitoring any consecutive reactions that occurred after the irradiation. For methanol, laser parameters such as output line frequency and power as well as irradiation time were varied. The effect of initial reactant pressure on the laser-induced dissociation of methanol was evaluated. Only methanol underwent a consecutive reaction. Hydrocarbon fragments were also observed from ethanol, 1-propanol, and 2-propanol. Methane, ethene, and ethyne were produced from ethanol. Propene, ethene, and methane were produced from 1-propanol, and methane and propene from 2-propanol. The products observed in some instances were different from those reported in the literature for pyrolytic and pulsed laser studies. The results from these investigations are compared with results from other similar compounds and similar techniques.