Vibrationally mediated photodissociation of molecules via excited electronic states

1 Vibrationally mediated photodissociation of molecules via excited electronic states 

Probably the first suggestion for utilizing the properties of laser light (the high intensity and short duration of radiation pulses) was (Letokhov 1969) to use the vibrationally mediated photodissociation of molecules via an excited repulsive electronic state with noncoherent isotope-selective saturation of the vibrational transition (Fig. 11.2). The isotope-selective two-step photodissociation of molecules consists of pulsed isotope-selective excitation of a vibrational state in the molecules by IR laser radiation and subsequent pulsed photodissociation of the vibrationally excited molecules via an excited electronic state by a UV pulse (Fig. 11.2(a)) before the isotope selectivity of the excitation is lost in collisions. Selective two-step photodissociation of molecules is possible if their excitation is accompanied by a shift of their continuous-wave electronic photoabsorption band. In that case, the molecules of the desired isotopic composition, selectively excited by a laser pulse of frequency uji, can be photodissociated by a second laser pulse of frequency uj2 selected to fall within the region of the shift where the ratio between the absorption coefficients of the excited and unexcited molecules is a maximum (Fig. 11.2(b)). 

The first experiment on isotope-selective dissociation was carried out with the and molecules, which could be selectively excited by C02-laser radiation 

2 Basics of IR multiple-photon excitation/dissociation of polyatomic molecules in the ground state 

The resonance MP excitation of molecular vibrations in an intense IR field forms the basis for several essentially different approaches to laser control. They can be classified according to the relations between the various relaxation times for the excited vibrational level interacting with the IR field  

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