LIFETIME-VIBRATIONAL INTERFERENCE EFFECTS IN THE RESONANTLY EXCITED X-RAY-EMISSION SPECTRA OF CO

A systematic study of vibrational band profiles in resonantly excited x-ray-emission spectra of free molecules is made. Carbon and oxygen K- emission spectra of CO following core excitations, using narrow-bandpa ss synchrotron radiation, to the 2 pi orbital an presented. Because of the short lifetime of the core-excited states, interference effects b etween close-lying coherently excited vibrational levels may occur. Th e importance of lifetime-vibrational interference in the carbon and ox ygen x-ray-emission spectra is investigated by comparing the experimen tal band profiles with simulated profiles. It is shown that to properl y describe the band profiles in the oxygen emission spectra it is nece ssary to include the interference contributions, while in the carbon s pectra the interference contributions are important only when the exci tation energy is tuned towards higher vibrational levels. For example, when the excitation energy is tuned to the upsilon=2 vibrational leve l significant interference effects are observed. It is also demonstrat ed how emission spectra recorded with a detuning of the excitation ene rgy from the resonance can be used to check the shape of the photon di stribution of the synchrotron radiation.