POLANYI RULES FOR ULTRAFAST UNIMOLECULAR REACTIONS - SIMULATIONS FOR HCO(CO)4(1)E)ASTERISK-]H+CO(CO)4

The traditional Polanyi rules for control of bimolecular reactions by selective investment of energy, e.g. preferentially translational, not vibrational energy for early-downhill reactions on attractive potential energy surfaces, are extended to ultrafast unimolecular reactions. Specifically, we consider photodissociations of the metal-hydrogen bond of HCo(CO)4(1E), occurring on a time scale of approximately 20 fs, much faster than competing intramolecular vibrational energy redistribution (IVR). Here the reaction path toward the products H + Co(CO)4 is hindered by a barrier located in the H + Co(CO)4 exit valley of the potential energy surface. In order to overcome this barrier and, therefore, to increase reactivity, vibrational energy should be invested selectively into the bond to be broken, i.e. [H-Col, not into complementary ''spectator'' modes, e.g. [CO-Co]. The required energetic preparation of reactants may be achieved by selective IR + UV two-photon excitations or by alternative techniques including frequency-selective UV single-photon photodissociation. The Polanyi rules for unimolecular reactions are demonstrated by fast Fourier transform (FFT) propagations of representative wave packets.