Isoelectronic ions, energies

There is an interesting similarity in the character of the solution absorption spectra of the isoelectronic ions Np3+ and Pu1 even though the absorption bands in Pu1 + are all shifted toward higher energies due to increases in both the electrostatic (Fk) and spin-orbit ( ) parameters, Table VI. We have also examined the spectra of complex alkali-metal Pu(IV)... 

In accordance with previous investigations [8,9], Aese experiments have shown a quite different behaviour for N (ls )than for other multicharged ions such as the isoelectronic ion [10. The single-electron capture process has been shown to be dominant on the n = 3 levels and in particular on the 3s level for collision energies lower than 50 keV. A high probability of double capture has also been observed characterized by an intense peak at X = 76.5 nm attributed to the 2s > 2s 2p P transition [4,5,7]. Furthermore,... 

The isoelectronic ions C104, SO4 ", and P04 have been studied by Johansen. " A medium size basis set was used, and regular tetrahedral geometry assumed. The energy-level order was in agreement with experiment. Other work on these molecules particularly concerned with the photoelectron spectrum has been reported. ... 

Ionization energy the quantity of energy required to remove an electron from a gaseous atom or ion. (12.15) Irreversible process any real process. When a system undergoes the changes State 1 State 2 State 1 by any real pathway, the universe is different than before the cyclic process took place in the system. (10.2) Isoelectronic ions ions containing the same number of electrons. (13.4)... 

The r(X ) = f(E) dependence being the same for molecular and crystalline halides, the radii of non-isoelectronic ions can be determined, provided the bond energies are known. The ionic radii for MX molecules and crystals are listed in Table 1.15, from which it follows that cationic and anionic radii change with to a similar degree. The radii of F (1.21 A), Cr (1.63 A), Br (1.71 A), and 1 (1.90 A) have been calculated from the Morse potential energy curves (calculated from the spectroscopic data) for the dissociation of molecular ions, X2 X +X,... 

Spectroscopic work on highly ionized atoms has been reviewed by Fawcett in two papers with comprehensive listings of references up to 1980. In the present review we will discuss the observed energy structure in representative sequences of isoelectronic ions. In some of these sequences the observations have now been extended to ions up to SO times ionized which provides excellent illustration of the Z dependence of the energy level structure. Many of these data have become available since 1980. 

The importance of the charges in ionic solids can be illustrated by comparing the energies involved in the formation of NaF(5) and MgO(s). These solids contain the isoelectronic ions Na, F , Mg +, and 0 . The energy diagram for the formation of the two soUds is given in Fig. 8.11. Note several important features ... 

The fluoride ion is the least polarizable anion. It is small, having a diameter of 0.136 nm, 0.045 nm smaller than the chloride ion. The isoelectronic E and ions are the only anions of comparable size to many cations. These anions are about the same size as K" and Ba " and smaller than Rb" and Cs". The small size of E allows for high coordination numbers and leads to different crystal forms and solubiUties, and higher bond energies than are evidenced by the other haUdes. Bonds between fluorine and other elements are strong whereas the fluorine—fluorine bond is much weaker, 158.8 kj/mol (37.95 kcal/mol), than the chlorine—chlorine bond which is 242.58 kJ/mol (57.98 kcal/mol). This bond weakness relative to the second-row elements is also seen ia 0-0 and N—N single bonds and results from electronic repulsion. 

In sharp contrast to the stable [H2S. .SH2] radical cation, the isoelectron-ic neutral radicals [H2S.. SH] and [H2S. .C1] are very weakly-bound van der Waals complexes [125]. Furthermore, the unsymmetrical [H2S.. C1H] radical cation is less strongly bound than the symmetrical [H2S.. SH2] ion. The strength of these three-electron bonds was explained in terms of the overlap between the donor HOMO and radical SOMO. In a systematic study of a series of three-electron bonded radical cations [126], Clark has shown that the three-electron bond energy of [X.. Y] decreases exponentially with AIP, the difference between the ionisation potentials (IP) of X and Y. As a consequence, many of the known three-electron bonds are homonuclear, or at least involve two atoms of similar IP. 

In the isoelectronic zirconates this absorption band is not observed [17]. The spectral position of these MMCT bands has been interpreted in terms of the relevant ionization potentials [17], an approach which runs parallel with the Hush theory [10]. The fact that the MMCT transition is at higher energy in the Cr(III)-Ti(IV) pair than in the Fe(II)-Ti(IV) pair is due to the more than 10 eV higher ionization potentials of the trivalent transition-metal ions compared to the divalent transition-metal ions. The fact that the MMCT absorption band is not observed in the zirconates in contradiction to the titanates is due to the higher ionization potential of the Ti(III) species ... 

These succesive isoelectronic processes may be represented, for the inmersion of a charged monoatomic ion A+ say, by the cycle described in Figure 1. Where X is an auxiliary isoelectronic neutral system. According to the cycle shown in Figure 1, we may write the insertion energy variation as follows ... 

Although not strictly a cation, the 1,2-dihydroborete [64] is isoelectronic with the monohomocyclopropenium ion [2], Cremer et al. (1984) carried out both semiempirical and ab initio calculations on the 1,2-dihydroborete [64], They concluded that the puckered geometry of [64] is the low-energy form and that there is appreciable (homoaromatic) interaction between the boron and C(3). 

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