A study of the excited state structure and vibrations of hydroquinone by ab initio calculations and resonant two-photon ionization spectroscopy

Hydroquinone (HYQ) in the lowest electronically excited state has been studied by ab initio quantum chemical calculations and resonant two-photon ionization (R2PI) spectroscopy. Calculations ar. the MP2/6-31G* and CIS/6-31G* levels yield satisfactory results on structures and vibrational frequencies of the cis-HYQ and trans-HYQ in both the S-0 and S-1 states. Only transitions involving in-plane modes are observed in the R2PI spectrum of HYQ. All spectral bands including some newly observed ones have been successfully assigned with the help of our computed results and analogy with the reported spectra for similar molecules. (C) 1997 Elsevier Science B.V.