Electronically excited molecules geometry

One of the most important advances in molecular quantum mechanics of the last fifteen years has been the increased ease and accuracy of predicting molecular conformation through purely theoretical models [1-4]. The stable geometries of molecules as yet unmade can be determined and molecular properties of these systems studied. The conformations and properties of electronically excited molecules can be examined theoretically, whereas experimentally these geometries are often very elusive. Transition states, the species that separates reactants from products, and that have but fleeting existence — if at all, experimentally — are also obtainable using molecular quantum quantum mechanics. 

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... 

Abstract. We present a quantum-classieal determination of stable isomers of Na Arii clusters with an electronically excited sodium atom in 3p P states. The excited states of Na perturbed by the argon atoms are obtained as the eigenfunctions of a single-electron operator describing the electron in the field of a Na Arn core, the Na and Ar atoms being substituted by pseudo-potentials. These pseudo-potentials include core-polarization operators to account for polarization and correlation of the inert part with the excited electron . The geometry optimization of the excited states is carried out via the basin-hopping method of Wales et al. The present study confirms the trend for small Na Arn clusters in 3p states to form planar structures, as proposed earlier by Tutein and Mayne within the framework of a first order perturbation theory on a "Diatomics in Molecules" type model. 

Due to differences in charge distribution in the various energy states of a molecule, the electronically excited species can be completely different in its chemical and physical behaviours as compared to the normal ground state molecule. Molecular geometries and internuclear force constants also change. 

Thus far, attention has been focused on the guest molecules in their ground states. This is so because it is relatively easy to predict and visualize the geometry and orientation of molecules within reaction cavities based on attractive and repulsive interactions between ground state guest molecules and the host structure. However, electronic excitation frequently lead to changes in molecular geometry and polarizability [97], For example, it is well known that formaldehyde becomes pyramidal upon excitation and the C—O... 

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