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![]() ![]() For typical valence-shell transitions the orbital of the excited electron is not much larger than the molecular core. 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 atoms the famous D-lines of sodium (3s,3p) are an example. Ītoms as well as molecules have electronic transitions that are not of the Rydberg type. 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). 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. The tetrahedral sulfate ion (Td) exhibits two unoccupied antibonding molecular orbitals ai and h of 3s and 3p character, respectively (Sekiyama et al. The spectra of acetylene, propyne and but-l-yne all show features characteristic of both types of electronic transition. įrom 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 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. 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 In-Phase ( 3s + 3s) Combination of Rydberg Orbitals Correlates to an s- type Orbital of the United Atom. The importance of the second 3d orbital decreases for second and, in particular, for third row transition metals. Adding the 4s and 4p orbital one is faced with an active space of 14 orbitals. ![]() 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. First row transition metals are, however, more demanding. One can normally leave the ns orbital inactive for main group atoms with more than three np electrons. ![]() It is usually sufficient to have the valence orbitals active, perhaps with added Rydberg type orbitals for studies of excited states. Electron capture in a Rydberg-type orbital can give. The types of excited states are depicted in Fig. 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. ![]()
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