The central CC bond stretch frequencies and structure of S-2 and S-1 diphenylacetylene in solution studied by picosecond time-resolved CARS spectroscopy

Picosecond time-resolved CARS spectra of diphenylacetylene and its C-13 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 species (lifetime approximate to 200 ps) as the S-1 state, The 2099 cm(-1) band 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 assignable to the normal modes which contain contributions of the central CC stretch vibration. The bond order of the central CC part decreases markedly in the S-1 state.