PICOSECOND TIME-RESOLVED FOURIER-TRANSFORM RAMAN-SPECTROSCOPY AND NORMAL-MODE ANALYSIS OF THE GROUND-STATE AND SINGLET EXCITED-STATE OF ANTHRACENE

Time-resolved Fourier-transform Raman spectra of the first singlet exc ited states of anthracene and deuterated anthracene have been measured with photoexcitation at 355 nm. Raman scattering was excited by 100-p s pulses at 1064 nm, resonant with the S-3 <-- S-1 transition. Continu ous wave (CW) Fourier-transform Raman spectra were also measured for a nthracene and anthracene-d(10) in the ground state. Ab initio calculat ions were carried out at the HF/6-31G and HF/6-31G levels for the gro und state and at the CIS/6-31G and CIS/6-31G levels for the excited s tate to generate a complete normal-mode analysis of both ground and ex cited states. Excellent agreement between the computational and experi mental Raman frequencies is observed for anthracene and anthracene-d(1 0) for both the ground and excited states after the computed frequenci es were scaled by a single scaling factor of 0.9. In several cases, co mparison with calculated frequencies allows previously ambiguous vibra tional assignments to be clarified. Evidence of interaction of the exc ited state with the solvent is observed for alkanes, but not alcohols, in an enhanced Raman intensity of solvent C-H stretching modes.