Ultraviolet resonance raman spectra and ab initio vibrational analyses of 1,4-benzoquinone: Reassignments of the ν₂and ν₃ bands

Ultraviolet resonance Raman (UVRR) spectra excited at 245 and 325 nm are reported for 1,4-benzoquinone and its ¹⁸O₂ and d₄ isotopomers. Depolarization ratios were determined for non-resonance Raman spectra excited at 647 and 441.6 nm and solvent effects were examined for the UVRR spectra. The UVRR bands at 1665 and 1639 cm^-1, the latter of which exhibited a much larger ¹⁸O₂ isotopic frequency shift than the former, are reassigned to ν₂ (in-phase C=O/C=C stretches) and ν₃ (out-of-phase C=O/C=C stretches), respectively, on the basis of the observed ¹⁸O₂ and d₄ isotope frequency shifts and unscaled ab initio vibrational analyses with the MP2 method using an extended basis set.