RESONANCE IONIZATION SPECTRA AS A REFLECTION OF EXCITED-STATE DYNAMICS

The MPI and multiphoton photoelectron spectra of CO2 contain many unusual features which we have not come to expect in the multiphoton spectroscopy of molecules. These include: 1) Above threshold absorption at relatively low laser powers. 2) Sharp structure in the MPI spectra due to autoionizing resonances. 3) Long vibrational progressions in photoelectron spectra, due to ionization of dissociating molecular levels. Pyrazine (1,4 diazine) is a classic molecule for the study of singlet-triplet coupling, being an intermediate case with respect to radiationless transitions. Two color threshold photoelectron spectra of S1 are able to distinguish between singlet and triplet state components. Lifetimes of these indicate that a fraction of the molecules decouple themselves from the singlet.