Photoelectron spectroscopic study of simple hydrogen-bonded dimers. II. The methanol dimer

HeI photoelectron spectra of a supersonic jet of methanol vapor have been obtained by using the temperature-controlled supersonic nozzle beam photoelectron spectrometer recently constructed in our laboratory. A HeI spectrum attributable to the methanol dimer (CH₃OH)₂ has been deduced by spectrum stripping. The first ten vertical ionization energies and the first adiabatic ionization energy of (CH₃OH)₂ have been determined from the stripped spectrum. Ab initio SCF MO calculations of ionization energies have also been carried out for (CH₃OH)₂ on the basis of Koopmans' theorem. The lower bound of the dissociation energy of (CH₃OH)₂⁺ has been estimated to be 1.2 ± 0.2 eV from the adiabatic ionization energies of the monomer and dimer. The equilibrium structure of (CH₃OH)₂ is also discussed.