Analysis of the absorption spectrum of the N V1 transition of cyclopentadiene

The ultraviolet absorption spectra of cyclopentadiene and cyclopentadiene-d6 were measured in the NV1 transition region. The spectra were analyzed to determine the excited state properties. The prominent vibrational progression was identified as a progression in the (predominantly) a1 C=C stretching vibration. A second, unidentified, vibrational interval was observed in the cyclopentadiene spectrum and inferred to exist in the spectrum of cyclopentadiene-d6. The excited state potential surface was deduced to be displaced 0.2 Å from the lower, predominantly along the C=C normal coordinate. The excited state lifetime was determined to be 37 fs at the origin and decrease at a rate inversely related to the excited state vibrational quantum number.