The photodissociation dynamics of [Ru(PH3)3(CO)(H)2] complex in the lowest two singlet excited electronic states has been theoretically analyzed. Reduced two-dimensional potential energy surfaces (PES) are built up by combining a time-dependent method to calculate the excited states energy with DFT (B3LYP) electronic calculations of the ground state. By means of a Fast Fourier Transform (FFT) algorithm the time evolution of the wavefunction upon vertical transition from the minimum of the ground state to both diabatic states has been followed. The propagation in S1, the lowest in energy at the vertical transition point and the one with a larger transition probability from the ground state, discloses that the system is not evolving from the initial position at least in the time spanned by the calculations. Conversely the H2 elimination is very fast (about 37 fs) in the S2 state. In this state the vertical transition puts the system in a purely dissociative zone of the PES. In that state FFT results indicate that the lengthening of the Ru-H2 distance and the shortening of the H-H one are taking place almost simultaneously. © 2002 Elsevier Science B.V. All rights reserved.