The photodissociation dynamics of the 3s Rydberg state of three ketones (CH3CO-R, R = C2H5, C3H7, and iso-C4H9) and the ensuing dissociation of the nascent acetyl radical following 195 nm excitation were investigated by ultrafast photoionization spectroscopy. The 3s state the lifetimes of these ketones are similar (2.5-2.9 ps), though lifetimes of the acetyl radical range from 8.6 ps for CH3CO-C2H5, 15 ps for CH3CO-C3H7, to 23 ps for CH3CO-(iso-C4H9), which suggests that for larger R more vibrational degrees of freedom compete for the excess energy so that less energy is partitioned into the internal energy of the acetyl radical. (C) 2003 Elsevier Science B.V. All rights reserved.