The nonequilibrium dynamics of intramolecular vibrational energy relaxation in cis-azobenzene after the excitation of each normal mode has been studied through the dynamic reaction coordinate analysis based on the PM3 molecular orbital method. With a high-excitation energy injected into a specific normal mode, a cis-to-trans isomerization reaction has been induced before the intramolecular vibrational energy redistribution is completed. This is a first finding (though in silico) of a nonequilibrium isomerization reaction of azobenzene triggered by the vibrational excitation, which is different from the usual optical and thermal isomerizations. A relevant model for describing this nonequilibrium, reaction is addressed. (C) 2002 Elsevier Science B.V. All rights reserved.