The ultrafast dynamics of the electronically excited ethylene molecule has been studied in pump-probe experiments with the pump wavelength of 198 nm and the probe wavelength of 790 run. The lifetime measured for the initially excited pipi* state is about 10 fs for C2H4 as well as for C2D4. No secondarily populated states of ethylene can be directly observed despite the high intensity of the probe pulses used. However, the observed time dependence of the fragment ions C2H3+ (C2D3+) and C2H2+ (C2D2+) suggests that they are formed by dissociative ionization via a secondary electronic state of ethylene. This result was confirmed by the time-resolved photoelectron spectra. (C) 2004 Elsevier B.V. All rights reserved.