SPECTROSCOPY AND PHOTOCHEMISTRY OF KETENE ADSORBED TO SODIUM-CHLORIDE

Infrared and ultraviolet absorption spectroscopies are used to investigate the photochemistry of ketene (CH2CO) adsorbed to a film of NaCl crystallites. The vibrational spectrum of adsorbed ketene resembles that of condensed and matrix-isolated samples: transition frequencies and intensities are only slightly modified. The electronic spectrum, however, shows significant shifts and enhancements due to adsorption. Following 185-nm excitation, adsorbed ketene dissociates with near unit efficiency. Secondary reaction of methylene radicals (CH2) is complete, producing ethylene (C2H4) and carbon monoxide (CO). For 254-nm excitation the quantum yield of dissociation is < 10(-2), significantly lower than in the gas. Quenching mechanisms are discussed in light of the known dynamical properties of ketene molecules and NaCl crystals.