The tunability of the CO2 molecular gas laser permits selective multiphoton infrared excitation of one isomer in a mixture of isomers. This capability can be exploited to drive isomerization reactions in a contra-thermodynamic direction. Examples of such reactions are the trans → cis isomerization of alkenes and the electro-cyclic isomerization of butadienes to cyclobutenes. It is also possible to achieve some selectivity in consecutive isomerization reactions (A → B → C) and in competing reactions (A B + C) via multiphoton infrared excitation. For example, consecutive reactions can be stopped at the intermediate product B in cases where the activation energy for B → C is lower than that for A → B. The product ratio B/C in competing reactions is, in some cases, dependent upon the average vibrational temperature of the reactant A and hence can be altered by changing laser fluence or collisional frequency. In addition, pulsed infrared lasers can be used to create high concentrations of vibrationally excited fragmentation products. We are currently seeking to correlate product vibrational energy distributions with reactant structure and decomposition mechanism.
ASJC Scopus subject areas
- Chemical Engineering(all)