Femtosecond time-resolved resonance Raman scattering (RRS) spectroscopy is used to investigate four bipyridinium radicals: methylviologen monocation MV + , benzylviologen monocation BV + , 4,4′-bipyridinium-N,N′-di(propylsulfonate) monoanion BPDPS -, and N,N′-ethylene-2,2′-bipyridinium monocation EB + . Time resolution of the dynamics of the four radicals using the 379.6 nm laser of 350 fs pulse duration is carried out by a pump and probe technique using the time-dependent transient intensity of Stokes and anti-Stokes RRS of the C-C stretching mode. It is found that the lifetime of the electronic excited state B 3u is less than 350 fs and the vibrational relaxation rates in the electronic ground state are some 2-5 ps. The possible vibrational relaxation mechanisms including the radical structure and charge effect on the vibrational relaxation are discussed. Assignments of some in-plane stretching vibrational modes for BV + and BPDPS -are tentatively made on the basis of the similarity of their molecular skeletons to those of MV 2+ , MV + , and BV 2+ . The shifts in vibrational frequency in the N-R mode are discussed according to the mass and charge effect of the substituted group R, whereas the frequency shifts in the C-C inter-ring stretching vibration upon reduction of BV 2+ to BV + are interpreted as the increase of inter-ring C-C bond order.

Formyl radical has been detected in zeolite NaY at room temperature by step-scan FT-infrared spectroscopy upon photodissociation of glycolaldehyde or acetaldehyde precursor. Identification was made by the CdO stretch absorption at 1847 cm -1 and a 13 C isotope shift of 40 cm -1 . The decay shows biphasic kinetics independent of the precursor used. In the case of glycolaldehyde, the final products recorded by static FT-IR spectroscopy can be explained by the exclusive reaction of HCO and CH 2 OH radicals. This allowed us to assign the initial decay with a lifetime of 24 ( 3 µs to geminate reactive encounters of HCO and CH 2 OH radicals. The subsequent long tail extending to 500 µs is well described by a second-order rate law consistent with nongeminate reaction of the radicals. This is the first direct kinetic observation of geminate and nongeminate radical reactions in a zeolite.