Equivalent states, chemically related molecules

H. Bock and B. G. Ramsey, Angew. Chem., 85, 773 (1973) Angew. Chem., Int. Ed. Engl., 12, 734 (1973), report on the interpretation of the PE spectra of main group element compounds by comparison of equivalent radical cation states of chemically related molecules, based on MO perturbation arguments. 

A. Comparison of Equivalent States of Chemically Related Molecules 583... 

Referring to the much recommended comparison of equivalent states of chemically related molecules 9 (cf. Figures 3 and 13 schemes 4, 8, 12 and 13), also for compounds of other elements like the recently PE spectroscopically characterized H3C-P=CH2113, advisable correlation with the ionization patterns of other iso(valence)electronic molecules like H3C-N=CH2 or H3C-C(H)=CH2 should always be preferred to fiddling around with nebulous d-orbitals. The answer to the title question is therefore straightforward no d —except as polarizing functions to improve basis sets for calculations of silicon compounds. 

The MPL spectrum exhibits two broad peaks, one at 467 nm (2.64 eV) and the other one at 422 nm (2.94 eV). These peaks appear to be related also to defects in the Si02 structure. Several such defect models have been discussed in the literature (47,48). The emission at 2.65 eV has been assigned to a new intrinsic defect in amorphous Si02 for which a two-fold coordinated Si is proposed, i.e., a Si(II) (neutral) center (48). Chemically, this is equivalent to the quasi-molecule Si02 with a 1Ai ground state, first excited singlet state, and a Bi triplet state. The... 

The topological state index (T ) of an atom represents the position of the atom in the scaffold of the molecular structure in relation to aU other atoms of the molecule (hut based on topology, i.e., on the connectivity and not on the three-dimensional structure) [54], Chemically and topologically equivalent atoms have identical indices. 

When finally the electron was discovered in 1897, it was realized that oxidation is equivalent to removal of electrons and reduction is equivalent to addition of electrons to the chemical system in question. It remained customary to associate oxidation state with atoms. For example, in the compounds H2S, S2, SO, SO2, and H2SO4, sulfur has the oxidation states -2,0, -1-2, -1-4, and -1-6, respectively. This is the formal oxidation state of an atom, which is important when the electrons in the chemical reaction are counted to find the stoichiometric coefficients in the reaction equation. The size of an added or removed electron is usually too large, due to the uncertainty relations, to be associated with a single atom. LiH, for example, can be regarded as Li+H , LiH, or Li H+, but there is no unique way to find out from the calculated density which case applies. The bonding valence electrons are distributed over the whole molecule. 

---