The central CC bond stretch frequencies and structure of S2 and S1 diphenylacetylene in solution studied by picosecond time-resolved CARS spectroscopy

Picosecond time-resolved CARS spectra of diphenylacetylene and its 13C 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 S2 state and the long-lived species (lifetime ≈ 200 ps) as the S1 state. The 2099 cm−1 band of the S2 state has been assigned to the central CC bond stretch while the 1577 cm−1 and 1557 cm−1 bands of the S1 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 S1 state.