The absorption spectrum of 1,3-cyclopentadiene in the 260-220 nm region exhibits some vibrational structure superimposed on a broad continuum. The depolarization ratios (p) of resonantly enhanced Raman transitions of the three strongest totally symmetric modes of vibration all deviate significantly from the value of 1 3 corresponding to a single electronic transition. This directly and unambiguously demonstrates the presence of two overlapping electronic transitions with perpendicular transition moments. The variation of p with excitation wavelength is consistent with association of the weak structured absorption with the transition to the 2A1 state, analogous to the 2Ag state of centrosymmetric polyenes, and the much stronger underlying continuous absorption with the transition to the 1B2 state, analogous to the corresponding 1Bu state of butadiene.
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry