2-methyl furan: An experimental study of the excited electronic levels by electron energy loss spectroscopy, vacuum ultraviolet photoabsorption, and photoelectron spectroscopy

The vacuum ultraviolet absorption spectrum of 2-methyl furan has been recorded between 5 eV (248 nm) and 9.91 eV (125 nm) and absolute photoabsorption cross sections measured. The electronic excited states of the molecule have also been probed using high resolution electron energy loss spectroscopy. Recorded under electric–dipole conditions, it has confirmed the magnitude of the photoabsorption cross section values and extended the optical oscillator strength values up to 12 eV. Measurements at several scattering angles have allowed the angular behavior of differential cross section ratios for some features in the 5–7.1 eV region to be measured, which in turn have helped in the assignments of electronic states to observed absorption bands. A high-resolution photoelectron spectrum was measured and allowed the two lowest ionization energies to be determined, these have been used in the identification of the related Rydberg states. Vibrational fine structure in the photoelectron spectrum has also been analyzed. The spectrum is dominated by intense $π–π*$ transitions. Rydberg series associated with the first and second ionization energies have been identified. The effects of symmetry reduction induced on the furan ring by the methyl substitution are also discussed.