Static properties of excited states

An excited state has a finite lifetime and so it has static properties, such as molecular shape (median bond lengths and angles) and dipole moment, like those of a ground-state molecule, that can in principle be determined experimentally. However, the lifetime of an excited state is short, often very short, and this restricts the range of techniques that can be employed to study such properties. Most of the available information comes from high-resolution absorption 01 emission spectra, particularly of small or symmetrical model compounds. The geometry of most other excited organic molecules has to be inferred from such results. 

The dipole moment of an excited state can be estimated from an analysis of solvent effects on absorption and emission spectra the 

Compound Nature of excited Slate Singlet energy kj 1001- Triplet energy/ kj moH 

An excited state has a characteristic lifetime under given conditions of temperature, solvent and concentration of substrate, and of other species in the solution. These lifetimes are short, varying from more than 10 s at liquid-nitrogen temperature for some of the longest-lived triplets to less than 10-l- s for some of the shortest-lived singlets. A small number of representative values are shown in Table 1.3. 

The enormous range of lifetimes, more than thirteen orders of magnitude, encompasses the wide variety of photophysical and photochemical processes that can occur for an excited state, since 

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