Photoinduced Reversible Electron Transfer Between the Benzhydryl Radical and Benzhydryl Cation in Amorphous Water-Ice

The benzhydryl radical is generated in high yields by flash-vacuum thermolysis of 1,1,2,2-tetraphenylethane with subsequent trapping of the product in argon or amorphous water at 3-4 K. Photoionization of the radical with various UV lights and electron sources produces the benzhydryl cation, which was identified by IR and UV-vis spectroscopy. In solid argon, the formation of the benzhydryl cation is irreversible, whereas in amorphous water-ice the electron transfer is reversible, and irradiation into the major absorption band at 443 nm of the cation leads back to the radical by electron attachment. Applications of ionization of organic matter trapped in water-ice to icy environments in astrophysics and planetary sciences, including Earth, are discussed.