High-resolution He Iα photoelectron spectroscopy of H2CO and D2CO using supersonic molecular beams

Abstract High resolution helium Iα (584 A) photoelectron spectra of H 2 CCO and D 2 CCO using supersonic molecular beams are reported. The adiabatic ionization energies (AIEs) of the electronic first, second, and fifth excited states are determined unambiguously. The doublet-like fine structures observed in the first excited states of ketene imply the excitation of a “soft” mode that was not observed before. Strong isotope effects are observed in the vibronic (vibrational) couplings in the ground state of ketene cations. The AIEs and spectroscopic constants for all six ionic states are reported to a much higher accuracy than previously available.