Controlling bond cleavage and probing intramolecular dynamics via photodissociation of rovibrationally excited molecules

Photodissociation studies of vibrationless ground state molecules pervade d iverse areas of chemical physics, while those of rovibrationally excited mo lecules are expected to have even more impact due to the additional fascina ting possibilities they offer and the new horizons they open. Photodissocia tion of rovibrationally excited species involves a double-resonance scheme in which a photodissociative transition is initiated from an excited rovibr ational state that might Substantially affect the intensity and wavelength dependence of the photoabsorption spectrum. In favourable cases, when the e nergy is disposed in vibrations that are strongly coupled to the reaction c oordinate, this pre-excitation might influence photodissociation pathways a nd lead to selective bond cleavage. In other cases it might influence the b ranching ratio between different fragments by altering the photodissociatio n dynamics. Moreover, the photodissociation of rovibrationally excited spec ies can serve as a sensitive means for detection of weak vibrational overto ne transitions of jet-cooled molecules, and therefore a promising way for r evealing specific couplings and time evolution of the prepared vibrational states. Experimental studies on different polyatomics are used to demonstra te the above aspects and to show how the mechanism of chemical transformati ons and the nature of rovibrationally excited states are highlighted by pho tolysis of these pre-excited molecules.