Singly Charged Cations

HeN in its ground state represents a van der Waals complex, whereas in the excited state HeN is covalently bound [4]. An earlier computation at an ab initio SCF level likewise yielded a weak bond in HeN (X Z ) of about 7 kJ/mol [5]. Other ab initio MO SCF calculations yielded a weakly bound ground state, one highly and two very weakly bound excited states [6]. CNDO/2 calculations of the binding energy and equilibrium distance were reported in [7]. 

HeN2 ions were created in a pulsed supersonic expansion jet (N2/He ratio 1 200) crossed close to the nozzle by an electron beam [8]. 

The photodissociation spectrum of HeN recorded in the 391-nm region exhibits two major vibrational bands the stronger band is almost coincident with the B -X origin transition of N2, while the weaker one, displaced 195 cm to higher energy from the more intense band, is a hot band of HeN which is associated with the 1-1 transition of N2. The similarity of this spectrum with that of Nj was interpreted by the ion being essentially a free internal rotor in both X and B electronic states. These results [8] confirmed the predicted absence of an appreciable barrier to rotation [9]. 

The two-dimensional interaction potential of the N2(X Sg)-He(X S) system was obtained from highly correlated ab initio MCSCF-CI calculations. The well depth, determined to be about 140 cm (0.017 eV), confirms a possible bound HeN ion. The well depth 

Studies of the vibrational excitation of N2 ions in collisions with He gave a rough estimate of 0.026 eV for the ion-molecule interaction energy in HeN [10]. 

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Such an electrode may, however, also show a response to certain other singly charged cations, and when an interfering cation C + is present in the test solution, an equilibrium is established between ions M + in the glass surface in contact with the solution, and the ions C + in the solution ... 

The alkali metals are usually found as singly charged cations. They react with water with increasing vigor down the group. Cations tend to form their most stable compounds with anions of similar size. 

From the values for the conventional enthalpies of hydration of the Group 1 cations (Table 2.4) and those of the halide ions (Table 2.5), it is clear that they differ enormously. This leads to the quest for absolute values, which can be compared on a more equal basis. Equations (2.17) and (2.22) connect the conventional and absolute values of cations and anions respectively, and an approximate value for Ahyd//TH +, g) may be obtained by comparing the conventional values of the enthalpies of hydration of the Group I cations and the Group 17 halide anions by using equation (2.16) modified for singly charged cations ... 

All fluorides with singly charged cations are soluble in water. 

Of the transition elements, only silver has a water-stable singly charged cation, Ag + (aq). Copper does have a stable + 1 ion in solid compounds, but this disproportionates in aqueous solution ... 

The diffusion constant for Cu can also be discussed using this model. Because diffusion by singly charged cation vacancies, and by neutral cation vacancies, are both important, we may write... 

Ethylenediamine, NH2C2H4NH2, is a base that can add one or two protons. The successive pKy values for the reaction of the neutral base and that of the monovalent (+1) cation with water are 3.288 and 6.436, respectively. In a 0.0100 M solution of ethylenediamine, what are the concentrations of the singly charged cation and of the doubly charged cation ... 

Suppose that, instead of 0.0100 mol NaOH, 0.0100 mol HC1 had been added to the solution in the previous problem. Calculate the molar concentrations of the singly charged cation, doubly charged cation, and neutral ethylenediamine. 

Several interesting trends are apparent on examining the data in Table V-4. For simple, singly-charged cations the limiting ionic conductances follow the order ... 

List six singly charged cations that are feeble acids. 

The second structural type that can be formed where the cation is small relative to the macrocycle is a bimetallic complex where the crown contains two metal ions. One example is the disodium complex of dibenzo[24]crown-8 (93), where each sodium ion is bound to three O atoms of the crown. Such complexes are relatively rare, and usually limited to singly charged cations, presumably for electrostatic reasons. 

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