The Rydberg 3p multiplet structure of the fenchone C band absorption
The vibrationally structured 3pz Rydberg excitation is identified and assigned in the VUV absorption spectrum of fenchone with an origin at 6.31 eV, below the prominent 6.4 eV (nominally 3p) band onset. This feature cannot, however, be observed in (2+1) REMPI spectra, as its relative excitation cross-section is much reduced in a two-photon transition. The 3py and 3px excitation thresholds, found to differ by only 10–30 meV, lie around 6.4 eV corresponding to the first intense band peak in both VUV and REMPI spectra. Calculations of vertical and adiabatic Rydberg excitation energies, photon absorption cross-sections, and vibrational profiles are used to support these interpretations.