Low-lying excited states

However, if the zeroth-order ground-state energy is well separated from low lying excited states, the diagonal... 

Wynne K, Haran G, Reid G D, Moser 0 0, Dutton P L and Hochstrasser R M 1996 Femtosecond infrared spectroscopy of low-lying excited states in reaction centers of Rhodobacter sphaeroides J. Rhys. Chem. 100 5140-8... 

Nearly every technical difficulty known is routinely encountered in transition metal calculations. Calculations on open-shell compounds encounter problems due to spin contamination and experience more problems with SCF convergence. For the heavier transition metals, relativistic effects are significant. Many transition metals compounds require correlation even to obtain results that are qualitatively correct. Compounds with low-lying excited states are difficult to converge and require additional work to ensure that the desired states are being computed. Metals also present additional problems in parameterizing semi-empirical and molecular mechanics methods. 

Use Configuration Interaction to predict the electronic spectra of molecules. The Configuration Interaction wave function computes a ground state plus low lying excited states. You can obtain electronic absorption frequencies from the differences between the energies of the ground state and the excited states. 

Singlet states with the same configuration as in Equation (7.59) with antiparallel spins of the electrons in the n 2p orbital are higher in energy and are low-lying excited states. 

This mode of hyperfine interaction will become important only when the impaired electron is able to partially occupy a low-lying excited state (AE small), and the ground state has orbital angular momentum (L 0). The adsorbed nitric oxide molecule and the superoxide ion with 170 are typical examples where hyperfine coupling via spin-orbit interaction may be observed. 

For the latter two ions, the presence of low-lying excited states makes the inclusion of both the first-order contribution of the excited states and the second-order effects due to coupling of the ground / state with the excited states crucial in a correct estimation of the room-temperature values of xT. Indeed, second-order contribution in Van Vleck [9] expansion of the susceptibility is inversely proportional to the energy difference between the ground and the excited states ... 

The wave functions of the ground and excited states of lanthanides have a truly multiconfigurational character.1 Therefore, computational description of both the ground state and the low-lying excited states, which are important for magnetic behaviour, is only possible by a multiconfigurational ab initio method. In this respect, the C ASSCF method proved to be a reliable tool for the description of electronic properties of lanthanide complexes. 

TABLE 6. CASPT2 vertical excitation energies (eV) for the low-lying excited states of butadiene, hexatriene and octatetraene0... 

The Mossbauer effect as a spectroscopic method probes transitions within an atom s nucleus and therefore requires a nucleus with low-lying excited states. The effect has been observed for 43 elements. For applications in bioinorganic chemistry, the 57Fe nucleus has the greatest relevance and the focus will be exclusively on this nucleus here. Mossbauer spectroscopy requires (a) the emission of y rays from... 

In the last few years, EPR has been widely used to study the electronic structure of four-and five-coordinated low-spin Co(II) complexes. Compounds of this class gained considerable interest because of their relation to biological oxygen carriers and to vitamin B12r. The ground state of the five-coordinated complexes is accepted to be dz2 ), in contrast to the four-coordinated compounds for which the determination of the correct ground state was quite troublesome, due to the fact that these types of Co(II) complexes have low-lying excited states. 

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