Picosecond Time-Resolved Fourier-Transform Raman Spectroscopy and Normal-Mode Analysis of the Ground State and Singlet Excited State of Anthracene

Abstract

Time-resolved Fourier-transform Raman spectra of the first singlet excited states of anthracene and deuterated anthracene have been measured with photoexcitation at 355 nm. Raman scattering was excited by 100-ps pulses at 1064 nm, resonant with the S_3 ← S_1 transition. Continuous wave (CW) Fourier-transform Raman spectra were also measured for anthracene and anthracene-d_(10) in the ground state. Ab initio calculations were carried out at the HF/6-31G and HF/6-31G* levels for the ground state and at the CIS/6-31G and CIS/6-31G* levels for the excited state to generate a complete normal-mode analysis of both ground and excited states. Excellent agreement between the computational and experimental Raman frequencies is observed for anthracene and anthracene-d_(10) for both the ground and excited states after the computed frequencies were scaled by a single scaling factor of 0.9. In several cases, comparison with calculated frequencies allows previously ambiguous vibrational assignments to be clarified. Evidence of interaction of the excited state with the solvent is observed for alkanes, but not alcohols, in an enhanced Raman intensity of solvent C−H stretching modes.