INFRARED FEL PHOTOCHEMISTRY - MULTIPLE-PHOTON DISSOCIATION OF FREON GAS

Wavelength tunability, synchrotron sidebands, and picosecond pulse str ucture are inherent characteristics of free-electron lasers (FELs) tha t should be advantageous for photochemistry involving multiple-photon photodissociation. Tuned to absorption resonance, the FEL sideband str ucture will overlap the broad, red-shifted, quasi-continuous excited-s tate absorption spectra and should lead to enhanced dissociation. The Los Alamos APEX FEL was operated with and without sidebands to test th is hypothesis on CFCl3 (Freon 11), one of the gases implicated as depl eting the ozone in the Earth's stratospheric layer. The FEL wavelength was set at the C-Cl stretch absorption resonance at 11.8 mum, the osc illator cavity length was detuned first to minimize and then to maximi ze the spectral bandwidth, and the beam was focused through a pair of test cells. Comparison of final and initial absorbance spectra indicat ed the CFCl3 photodissociation yield was 1.2% for the cell exposed wit h sideband spectra (3% FWHM) and 9-ns micropulse separation. Negligibl e effect was seen without sidebands, albeit at lower total beam fluenc e.