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 potenti al energy surfaces, are extended to ultrafast unimolecular reactions. Specifically, we consider photodissociations of the metal-hydrogen bon d of HCo(CO)4(1E), occurring on a time scale of approximately 20 fs, m uch faster than competing intramolecular vibrational energy redistribu tion (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 po tential energy surface. In order to overcome this barrier and, therefo re, to increase reactivity, vibrational energy should be invested sele ctively into the bond to be broken, i.e. [H-Col, not into complementar y ''spectator'' modes, e.g. [CO-Co]. The required energetic preparatio n of reactants may be achieved by selective IR + UV two-photon excitat ions or by alternative techniques including frequency-selective UV sin gle-photon photodissociation. The Polanyi rules for unimolecular react ions are demonstrated by fast Fourier transform (FFT) propagations of representative wave packets.