Energy selectivity electronic excitation

The electronic excitation of a reagent can have several effects on a chemical reaction. For example, it can convert an endothermic reaction into an exothermic one, with subsequent enhancement of the reaction yield. This energy barrier reduction is what occurs 

A state of the reagent (an eigenstate or superposition of eigenstates) that localizes energy in some part of the molecule must be excited. 

The energy must remain localized during the reaction, (non-ergodic behaviour). It is necessary for the reaction to occur before the excitation energy becomes statistically distributed among the available degrees of freedom (non-randomization), otherwise vibrational excitation is no more effective than heat. 

The state prepared by the selective excitation must promote or hinder reactivity of that portion of the molecule, so that a change in the product-branching ratio can 

The process is about 70kJ mol endothermic for 0( P), but 120 kJ mol exothermic for 0( D). That an electronic excitation of the reagents promotes its chemical reactivity is not always the case. For example, the reactivity of ground-state oxygen with nitrogen atoms 

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Using visible-ultraviolet spectroscopy of molecules, we examine the nature of excited electronic states since typically the absorption of a photon in this energy region electronically excites the molecule. For molecules composed of elements with low atomic number, the strongest selection rule at work in visible-ultraviolet spectroscopy is... 

XPS is also often perfonned employing syncln-otron radiation as the excitation source [59]. This technique is sometimes called soft x-ray photoelectron spectroscopy (SXPS) to distinguish it from laboratory XPS. The use of syncluotron radiation has two major advantages (1) a much higher spectral resolution can be achieved and (2) the photon energy of the excitation can be adjusted which, in turn, allows for a particular electron kinetic energy to be selected. 

A further technique exists for the determination of triplet energy levels. This technique, called electron impact spectroscopy, involves the use of inelastic scattering of low-energy electrons by collision with molecules. The inelastic collisions of the electrons with the molecules result in transfer of the electron energy to the molecule and the consequent excitation of the latter. Unlike electronic excitation by photons, excitation by electron impact is subject to no spin selection rule. Thus transitions that are spin and/or orbitally forbidden for photon excitation are totally allowed for electron impact excitation. 

Table 3. Excitation energies of selected electronic states of H2 (in cm...

By energy transfer from electronically excited SOj, the 13 vibrational level of CO can be selectively populated. 

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