Excited-state geometry

It should be noted that no geometrical relaxation of the excited state geometry was considered in our calculations. Such relaxations may well occur to some degree and would then enhance the localization of the electronic excitation. However the relatively narrow spectral bandwidth suggests that the geometrical changes associated with excitation into the first excited singlet state are only minor. 

Shukla MK, Mishra PC (1999) A gas phase ab initio excited state geometry optimization study of thymine, cytosine and uracil. Chem Phys 240 319... 

Shukla MK, Leszczynski J (2005) Effect of hydration on the lowest singlet jiji excited-state geometry of guanine a theoretical study. J Phys ChemB 109 17333-17339... 

However, one of the few sources of information regarding the configurations of molecules in their electronically excited states is electronic spectra. Consequently the excited state geometries of relatively few molecules are known to date. The most accurate method for the determination of excited... 

It is expected that as the ability of spectrometers to resolve closely spaced rotational and vibrational bands from molecular spectra improves, the number of molecules whose excited state geometries are known will increase. However, it must be realized that the task of determining excited... 

We are all well aware of the tremendous advances over the past decade in both the quality and number of X-ray structural studies on molecules and ions, aimed at the accurate determination of the ground-state geometries. However, our knowledge of excited-state geometries has not developed at a comparable rate, and few techniques can be brought to bear upon this problem. 

Unfortunately, the above analysis can never be widely applicable to the determination of excited-state geometries since so few molecules and ions exhibit vibronically structured absorption bands and excitation profiles, even at low temperatures. Moreover, some questions arise as to the possible breakdown of the Condon approximation. Other types of molecule for which similar analyses have been carried out include 3-carotene, carotenoids (9) and certain carotenoproteins such as ovorubin (10). In these cases the excitation profiles of three skeletal a bands are monitored, and estimates for the change in C-C and C=C bonds lengths ( 0.02 A) have been made. 

For cluster breakdown to occur, therefore, we must consider two stages, (i) The formation of an excited state geometry which contains CO bridges and must satisfy the criteria laid out above, i.e., there must be sufficient CO groups per metal atom within the cluster to produce a saturated unit. This will require an energy Et. (ii) The ejection of the saturated unit, which will require an additional energy E2. 

Figure 4.19 Ground slate and excited state geometry of formaldehyde molecule.

F. Dorr, Polarized light in spectroscopy and photochemistry . Reference T. Excited State Geometries... 

For this molecule the almost featureless crystal spectra do not allow such a detailed analysis of the excited state geometry and potential surface to be made. 

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