Acetic acid electronic state spectroscopy by high-resolution vacuum ultraviolet photo-absorption, electron impact, He(I) photoelectron spectroscopy and ab initio calculations

Electronic state spectroscopy of CH3COOH has been investigated using Vacuum UltraViolet (VUV) photo-absorption spectroscopy in the energy range 3.5-10.6 eV. The availability of a high-resolution photon beam (∼0.075 nm) has allowed detailed analysis of the vibrational progressions and allowed us to propose, for the first time, new assignments for several Rydberg series. Excited states located in the 10-14 eV region have been studied for the first time. The VUV photo-absorption spectrum is compared with the electron energy loss spectrum (EELS) recorded in dipolar transition mode (100 eV incident energy, ∼0° scattering angle) in the 5.0-14 eV energy loss range. A He(I) photoelectron spectrum has also been recorded from 10.5 to 13 eV and compared to earlier low resolution works. A new value of (10.657 ± 0.002) eV for the ground ionic state adiabatic ionisation energy is proposed. All spectra presented in this paper represent the highest resolution data yet reported for acetic acid. New ab initio calculations help in the assignment of the spectral bands.