Photoatomic effect: Light-induced ejection of Na and Na₂ from polydimethylsiloxane surfaces

The photoejection of Na and Na-2 from surfaces prepared by adsorption of sodium vapor on solid films of polydimethylsiloxane (PDMS) of various molecular weights and structures is found to be dependent on light intensity and frequency. At low power levels the desorption yields of Na and Na-2 are linear functions of desorbing light power and exhibit frequency thresholds for photoejection analogous to the photoelectric effect. The frequency thresholds an 9500 cm(-1) for Na and 11 500 cm(-1) for Na-2, and the 2000-cm(-1) difference can be accounted fur with a model in which the alkali-metal species form charge-transfer complexes Na (+)PDMS(-) and Na(2)(+)PDMS(-), with the cations stabilized by interaction with the oxygen atoms of the PDMS polymer backbone. The ejection mechanism take place by a reverse charge transfer to form a less polar complex with enough energy to eject Na or Na-2 from the surface.