High resolution photoelectron spectroscopy and femtosecond intramolecular dynamics of H2CO+ and D2CO+

High resolution helium Iα (584 A) photoelectron spectra of H2CO and D2CO are reported. The present study reveals much new vibrational structure detail in the ionic first excited state of formaldehyde. Weak excitations of the ν3 (in H2CO) and ν1 (in D2CO) modes along with the strong excitations of the ν2 mode in the ionic first excited states are fully resolved for the first time. The weak excitations of the ν4 out-of-plane bending mode in the ionic ground and first excited states of formaldehyde cations indicate that they may have nonplanar equilibrium geometries. Strong isotope effects on vibronic (vibrational) couplings are observed in the cation first and second excited states. Vibrational autocorrelation functions are calculated from the high-resolution photoelectron spectra. The correlation functions calculated for the first electronic excited states show rather slow decay rate on the femtosecond time scale. The ultrafast decay of the formaldehyde cations implied by the correlation functions calculated for the third electronic excited states suggest that dissociation and intramolecular dynamic processes are the main decay pathways