Atomic and Diatomic Ions

Studies of the photophysics and photoreactions of atomic and diatomic ions which have appeared this year are collected in Table 17, and those dealing with polyatomic ions are presented in Table 18. 

Dimopoulou-Rademann. K. Rademann, P. Bisling, B. Bnitschy, and H. Baiimg el. Ber. Bunsenges. Phys. Chem., 1984, 88, 215. 

Yamanouchi, H. Watanabe, S. Koda, S. Tsuchiya, and K. Kuchitsu, Chem. Phys. Lett., 1984, 107, 290. 

Leone and co-workers have developed a new apparatus for the study of single collision ion-molecule reactions. They demonstrated their techniques in a study of the reaction N ( P) + CO(X 5 ) N( S) + CO (X 2+),tj,J, in which thermal ions were produced, expanded in a He buffer into a low-pressure chamber, and crossed by a stream of reactant CO molecules. The nascent rotational and vibrational states of the CO product were probed using LIF. Emission in the wavelength range 350—500 nm has been observed to accompany the reaction of N ( D) ions with H2 and The emission was assigned 

Numerical calculation of two-photon dissociation cross-sections for HJ. Cross-sections are small for low vibrational levels but increase rapidly with increasing vibrational excitation Spectroscopic study of ion photofragments resulting from the 193 nm photodissociation of H2, HD, DJ, 020 , OD, ND3, and NDJ 

---

The formula units He and F2 represent single atoms and diatomic molecules, respectively. Unlike the F2 molecule, in which one fluorine atom is bonded to a specific other fluorine atom, in the ionic compound NaCl, one Na ion is bonded to six Cl ions that are adjacent to it. Each of the Cl ions is bonded to six Na ions that are adjacent to it. (The fifth and sixth ions are in layers in front of and behind the layer shown here see Figure 5.9.) The ratio of Na" ions to CF ions is therefore 1 1. Any pair ofNa+ andCr ions, such as those circled in red or the one circled in green, is a formula unit. 

The lattice energy which we have discussed above is the amount of work which must be expended to disperse a crystal into an assemblage of widely separated ions. As such it cannot be immediately compared with any readily measurable quantity, and, in particular, is not to be identified either with the heat of sublimation, which is the energy necessary to disperse the crystal into a molecular gas, or with the chemical heat of formation, which is the energy released when the crystal is formed from metal atoms and diatomic halogen molecules. In... 

The atomic orbitals were determined (numerically) together with the two co-efficients. Similar MCSCF calculations on atoms and negative ions were simultaneously performed in Kaunas, Lithuania, by A. Jucys [10]. The possibility was actually suggested already in 1934 in the book by I. Frenkel [11]. Further progress was only made with the advent of the computer. A.C. Wahl and G. Das developed the Optimized Valence Configuration (OVC) Approach, which was applied to diatomic and some triatomic molecules [12,13]. 

The Ground-State Energy of Atomic and Molecular Ions On the neutral diatom point N = Z, this evidently yields 1 SE... 

The vapours of metals are, as we have seen, quite different from the solids and liquids. In general, metals vaporize into a mixture of atoms and diatomic molecules, the proportion of the latter diminishing with increase of temperature. Thus, sodium metal just above the boiling point contains about 99% of sodium atoms and 1% of Na2 molecules. On vaporization of a metal, therefore, the individual ions or pairs of ions become separated from each other, carrying their electrons with them. The mechanism for the conduction of electricity accordingly breaks down, and metallic properties disappear. 

As an example of the MO treatment, let us consider the case of a diatomic molecule (AB) with two electrons in the presence of a bare proton. For our specific example, we will neglect the resonance interaction between the molecule and the ion using fiAC = jiBC = 0, where C designates an atomic orbital on the proton site. 

A solid that contains cations and anions in balanced whole-number ratios is called an ionic compound. Sodium chloride, commonly known as table salt, is a simple example. Sodium chloride can form through the vigorous chemical reaction of elemental sodium and elemental chlorine. The appearance and composition of these substances are very different, as Figure 2-24 shows. Sodium is a soft, silver-colored metal that is an array of Na atoms packed closely together. Chlorine is a faintly yellow-green toxic gas made up of diatomic, neutral CI2 molecules. When these two elements react, they form colorless ciystals of NaCl that contain Na and Cl" ions in a 1 1 ratio. 

Consider a stable diatomic molecule with nuclei denoted as A and B. The Born-Oppenheimer potential V for such a molecule will depend on the internuclear distance rAB and will typically have the form shown in Fig. 3.1. The potential energy has a minimum at r0, which is often referred to as the equilibrium internuclear distance. As the distance rAB increases, the potential V increases and finally reaches a limiting value where the molecule is now better described as two separated atoms (or depending on the electronic state of the system, two separated atomic species one or both of which may be ions). The difference in energy between the two separated atoms and the minimum of the potential is the dissociation energy De of the molecule. As the internuclear distance of the diatomic molecule is decreased... 

Charge-transfer and dissociative-charge-transfer reactions of diatomic ions with various molecules that yield luminescence spectra are summarized in Table IV.B, part 3. In some of these, for example, the H2+ —N2 reaction, vibrational and rotational excitation have again been observed to accompany electronic excitation.155, 426 Molecular-ion reactions are generally accompanied by more extensive rotational excitation of the products than occurs with atomic-ion reactions.439... 

---