Electronically excited isomers

ONE-ELECTRON PSEUDO-POTENTIAL INVESTIGATION OF Na(3p P)Ar CLUSTERS ELECTRONICALLY EXCITED ISOMERS AND EMISSION SPECTRA... 

II) isomer. Optical excitation of II yields N, which rapidly rearranges to give a different electronically excited isomer, namely the "tautomer" form (T ). The fluorescence maxima for the N and T forms are 413 nm and 543 nm, respectively. 

Obviously, a great deal more information could be obtained if the isomeric ions could be probed spectroscopically. Vibrational states of the various isomers are not generally well known, but some structural information is available. Thus, the rotational structure of vibrational transitions may provide a better signature for particular isomers. Certainly, insufficient data are available about the potential surfaces of electronically excited states for electronic excitation to be used as a probe, e.g., as in the very sensitive laser induced fluorescence. At present, there are sensitivity limitations in the infrared region of the spectrum, but this may well be an avenue for the future. The study of isomeric systems and their potential surfaces has just begun ... 

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. 

They are listed in Table 1 for the various electronically excited stable isomers The transition dipole moments from these electronic excited states (j>k at equilib-... 

The fluorescence quantum yield of 448 is 0.14, a sixfold increase relative to that of the parent. In comparison, the fluorescence quantum yield of 449 (0.01) is comparable to that of the parent compound. The phosphorescence emission quantum yield of 449 is 0.56 in a frozen matrix as expected as a result of the intramolecular heavy atom effect. In contrast, the phosphorescence is effectively shut off in the anti-isomer where the quantum yield is only 0.04. This observation suggests that the electronic excited state structures and nonradiative decay channels very considerably with constitution of the isomers. The optical gap energy was 3.1 (3.3) eV for 448 (449). 

The conversion of trans- to cis-stilbene by irradiation of either W(CO)6 or Mo(CO)6 is consistent with production of an excited metal carbonyl-stilbene complex which undergoes isomerization promptly.136, 137 The generation of the cis isomer represents movement away from the thermodynamic ratio of cis- and frans-stilbene which is 100% trans. Thus, an electronically excited state must be important in the reaction sequence. Two proposals have been made 137 (1) excitation of an M(CO) (stilbene)6 complex leads to a sigma bonded diradical intermediate as shown in reaction (49) or (2) electronic excitation may yield a perturbed IL excited state as for the styrylpyridine complexes discussed above. The sigma bonded olefin diradical... 

Recently, Adam and coworkers reinvestigated the Paterno-Buchi reaction of cis- as well as Jnms-cyclo-octene (136) with electronically excited benzophenone (Sch. 46) [135]. They reported an unprecedented temperature-dependent diastereoselectivity, where the more stable substrate diastereo-isomer (c/s-cyclo-octene) leads, with increasing reaction temperature, to... 

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