Rydberg excitation

The isomer lowest in energy is predicted to be the 2,5-dihydro-1,2,4-triazine 198g. The most stable structures always show two C=N double bonds. Moreover, in polar solvents, 198h should also be a dominant species [00PCCP2187]. The valence and Rydberg excited states of 1,2,3-triazine have been studied by multireference methods (MRD-CI) and the results are compared with experimental spectra [98CP39]. 

An obvious remedy to this situation is to use potentials that by construction exhibit the correct asymptotic behavior. Indeed, using the LB94 or the HCTH(AC) potentials yields significantly improved Rydberg excitation energies. As an instructive example, we quote the detailed study by Handy and Tozer, 1999, on the benzene molecule. These authors computed a number of singlet and triplet n->n valence and n —> n = 3 Rydberg excitations... 

It should be noted with respect to method 1 that in most Rydberg excitation experiments to date pulsed lasers have been used even to obtain the highest resolution spectra, and this naturally precludes the measurement of lifetimes longer than -10 ns. 

TDDFT places Rydberg excitation energies also too low [91-93],... 

The MS-CASPT2 method should be used when it is suspected that several CASSCF states are close in energy, a situation that often obtains in photochemistry where close avoided crossings are common and even conical intersections. It may also be crucial in order to separate valence and Rydberg excited states as illustrated in the original publication for the case of ethylene. Another example was given by Merchan and Serrano-Andres in a study of the excited states of n-tetrasilane [52],... 

Nakatsuji, H. (1983). Cluster expansion of the wavefunction. Valence and Rydberg excitations, ionization and inner-valence ionizations of COj and NjO studied by the SAC and SAC Cl theories. Chem. Phys. 75, 425-41. 

In the expansion 22 the expressions in parentheses represent zeroth-order excitations localized at the carbonyl or cyclopropane moieties, respectively. The term CT includes charge-transfer components and depends upon the extent of mesomeric interactions between the subunits. The sum in equation 22 is over all the HOMO - LUMO (3e, 4e ) transitions of cyclopropane (cf. Subsection III.A). Actually, of course, more excitations have to be included into expansion 22. In particular, expansion 22 does not include Rydberg excitations. 

Rydberg excited states of ANI and its derivatives have been located72,143. A novel band located between the first and second it — n transitions, and centered at 37104 cm-1 (4.62 eV above the Sq and 0.38 eV above the, Y state), has been observed72. This singlet 1 B state has been assigned to a 3s-Rydberg state161. 

O. Kitao and H. Nakatsuji, Cluster expansion ofthe wave function. Valence and Rydberg excitations and ionizations of benzene,./. Chem. Phys. 87, 1169-1182 (1987). 

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