THE CENTRAL CC BOND-STRETCH FREQUENCIES AND STRUCTURE OF S-2 AND S-1 DIPHENYLACETYLENE IN SOLUTION STUDIED BY PICOSECOND TIME-RESOLVED CARSSPECTROSCOPY

Picosecond time-resolved CARS spectra of diphenylacetylene and its C-1 3 species were reported. CARS bands due to two transient species with different lifetimes were observed, The short-lived species (lifetime < 20 ps) has been identified as the S-2 state and the long-lived specie s (lifetime approximate to 200 ps) as the S-1 state, The 2099 cm(-1) b and of the S-2 state has been assigned to the central CC bond stretch while the 1577 cm(-1) and 1557 cm(-1) bands of the S-1 state are assig nable to the normal modes which contain contributions of the central C C stretch vibration. The bond order of the central CC part decreases m arkedly in the S-1 state.