Photochemistry of 2+: Wavelength, Pressure, and Medium Dependence of Redox and Aquation

Article abstract of DOI:10.1021/j100239a031

The ratio of redox to aquation of ²⁺ has been shown to be constant at about 2 for irradiation wavelengths (nm) of 254, 275, 313, and 365, falling close to zero at 514.5.With increasing pressure, quantum yields for redox and aquation decrease, the former somewhat faster, and in a wavelength-dependent fashion, so that the apparent volumes of activations (mL mol^-1) for redox and aquation are respectively 6.0+/-0.6 and -0.4+/-3.2 at 365 nm and 4.8+/-0.3 and 2.5+/-2.7 at 313 nm.At ordinary pressure at redox yield falls 8-fold and the aquation yield increases 50percent in 40 wtpercent glycerol/water.The equations relating volumes of activation for individual reaction steps to the overall apparent volumes of activation for the lifetime and quantum yield are derived.It is shown that all of the above observations are supportive of a mechanism involving generation of a caged radical pair which has no memory of the excitation enrgy of its progenitor.