Rydberg-type orbital

Another interesting and important feature of collisional reduction of cations is that the reducing electron can enter a high molecular orbital corresponding to an excited state of the neutral molecule, radical, or biradical. The types of excited states are depicted in Fig. 3. Electron capture in a Rydberg-type orbital can give... 

This is the simplest case. It is usually sufficient to have the valence orbitals active, perhaps with added Rydberg type orbitals for studies of excited states. One can normally leave the ns orbital inactive for main group atoms with more than three np electrons. First row transition metals are, however, more demanding. It has been shown that in order to be able to accurately describe the relative correlation effects in atomic states, which differ in the number of 3d electrons, one needs to use two sets of d-orbitals, 3d and 3d where the second set describes the strong radial correlation effects in the 3d shell [29]. Adding the 4s and 4p orbital one is faced with an active space of 14 orbitals. The importance of the second 3d orbital decreases for second and, in particular, for third row transition metals. 

The In-Phase ( 3s + 3s) Combination of Rydberg Orbitals Correlates to an s-type Orbital of the United Atom... 

The lowest A, excited states of C3H2are of Rydberg type, arising from the promotion of one electron from the carbene lone pair orbital to 3s and 3p Rydberg orbitals, are better represented by orbitals generated by a MCSCF/SD treatment (Table 9). 

The same conclusion, that MCSCF/SD expansions using orbitals optimized for the ion provide a better representation, is reached for the lowest states of 82 symmetry which are also states of Rydberg type arising from an in-plane excitation from the carbene orbital. 

From spectroscopic data it seems likely that the excited states involved in alkyne photochemistry are either (tt, — ) states, in which an electron from a bonding tt molecular orbital has been promoted to an antibonding - molecular orbital, or Rydberg stales, in which a tt electron has been promoted to an extended a-type orbital covering more than one nucleus. The spectra of acetylene, propyne and but-l-yne all show features characteristic of both types of electronic transition. In... 

The tetrahedral sulfate ion (Td) exhibits two unoccupied antibonding molecular orbitals ai and h of 3s and 3p character, respectively (Sekiyama et al. 1986 Tyson et al. 1989 Hawthorne et al., 2000 Myneni 2000). The 15— ai transitions are dipole-forbidden (because of the 5-character of a orbitals), and the intense features in the NEXAFS spectra of sulfate correspond to the 15—orbitals (Fig. 27). The high-energy features above these intense bound state transitions correspond to the Rydberg-type transitions of 3d character or continuum state transitions (Table 4—in Appendix). 

Atoms as well as molecules have electronic transitions that are not of the Rydberg type. For atoms the famous D-lines of sodium (3s,3p) are an example. For molecules all the familiar (vr, n ) and (n, rr ) transitions of olefins and aromatic molecules are examples of non-Rydberg, valence-shell (or intravalency) type transitions. For typical valence-shell transitions the orbital of the excited electron is not much larger than the molecular core. Bands due to such transitions cannot be ordered into series. The orbital of the excited electron is usually antibonding in one or more bonds wliile Rydberg orbitals because of their large size are, in most cases, essentially non-bonding. 

The prediction of molecular Rydberg spectra, as well as the analysis of the available laboratory data, has constituted a challenge on the theory. A number of ab initio calculations have been carried out on transition probabilities of Rydberg molecules, such as the frequently quoted Hartree-Fock (HF) study of H3 by King and Morokuma (15), the self-consistent-field frozen-core calculation with floating-spherical-Slater-type orbitals (FSSO) on the second-row Rydberg... 

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