Multiphoton ionization photoelectron spectroscopy of acetaldehyde via the (A)over-tilde (1)A '', (B)over-tilde, (C)over-tilde, and (D)over-tilde states

REMPI spectra are reported for the acetaldehyde (A) over-tilde (1)A", (B) o ver-tilde, (C) over tilde, and (D) over-tilde states. Photoelectron spectro scopy is used to probe the nature of the intermediate states, measure the c ation vibrational frequencies, and to identify useful routes for preparing state-selected ions. Ab initio calculations of neutral and cation vibration al frequencies are also reported. The (B) over tilde state is found to be a well-behaved Rydberg state, but with some distortion relative to the catio n geometry along the nu (10) and nu (15) coordinates. There are (B) over ti lde state REMPI transitions that produce well state-selected cations, with vibrational energies of up to 0.4 eV, and several new cation frequencies ar e observed. The (A) over tilde (1)A" state gives structured, if somewhat br oadened, REMPI transitions, but ionizes to produce a broad population of vi brationally hot ions. Only the origin band of the (C) over tilde state is o bserved in REMPI, despite high intensity for this state in absorption. A fe w (D) over tilde state transitions are sharp, and ionize to produce cold ca tions, as expected for a good Rydberg state. Most (D) over tilde state leve ls are strongly mixed and broadened, however, and ionize to hot cations. In consistencies in the literature are discussed in light of the photoelectron spectra and ab initio results. (C) 2001 American Institute of Physics.