Electron spectroscopy of resonance-enhanced vibrational excitations of gaseous and solid tetrahydrofuran

We report intramolecular vibrational excitation of tetrahydrofuran (THF) in both the gas and solid phase induced by 1–30 eV electrons. High-resolution electron-energy-loss spectra reveal selective vibrational enhancement of THF for different impact energies, indicating the presence of at least three resonances (i.e., temporary anion states), located near 4, 7.5, and 10 eV, as well as many possibly overlapping higher-lying resonances. We also report electron-energy-loss spectra for different THF film thicknesses. Besides fundamental vibrational excitation, we observe several energy loss peaks due to overtones and combination vibrational modes. The present vibrational losses are assigned in compliance with published optical measurements. The similarities between the solid THF and gaseous cyclopentane spectra suggest that the resonances in both molecules could have a common origin and hence need not be attributed to the presence of the oxygen nonbonding electrons in THF.