Diatomic molecules electron affinity

Symbol Br atomic number 35 atomic weight 79.904 a halogen group element electron affinity 3.36359 eV electronegativity 2.8 electron configuration [Ar] 3di°4s24p5 most stable valence states -1 and -i-5, less stable valence states -1-1 and -i-3 a diatomic molecule (Br2) in liquid and vapor states over a wide range of temperature two stable isotopes, Br-79 (50.57%) and Br-81 (49.43%). 

Mulliken proposed (1934) that electronegativities could be obtained from ionisation potentials and electron affinities (we use here the terms appropriate for atoms, rather than atomic substances). If the bonding in a diatomic molecule AB can be represented by the resonance structures ... 

More input information is required to perform a CNDO calculation than an EH calculation. The same requirements for choice of atomic orbitals and ionization potentials, described before for EH, must be made. In addition, electron affinity data for each orbital must be employed and usually this is known with least accuracy. Tables of data for some orbitals have been compiled by Zollweg (31) however, in some cases these data must be estimated. The resonance parameter must be chosen by some procedure for each kind of atom. Pople et al. (2) have recommended values for low atomic number elements, and the fitting of calculated to experimental diatomic molecule data has been used (30) as a criterion for choice in other work. Table I lists input data that we have used for previous MO calculations. 

The asymptotic behavior of the exchange-correlation potential far from the molecule has been identified as the key factor determining the accuracy of the ionization potentials of anions and electron affinities of neutral molecules.5 Recently, Wu et al.91 proposed a variational method, which enforces the correct long-range behavior of vxc. Indeed, a noticeable improvement compared to the Kohn-Sham results derived using conventional approximations (LDA-, GGA-, and hybrid functionals) was reported for atoms (H, He, Li, Be, B, C, N, O, and F) and diatomics (BeH, CH, NH, OH, CN, BO, NO, OO, FO, and FF). The still significant discrepancies between the experimental and calculated ionization potentials (or electron affinities) were attributed to errors of the exchange-correlation potential in the molecular interior. 

Figure 2.2a illustrates the most general type of electron capture by a diatomic molecule. The asymptote of the dissociative AB curve lies below the asymptote of the AB curve by an amount equal to A(B), the electron affinity of B. Since the speed of the incident electron will be large, the nuclei may be considered at rest during the time in which attachment takes place. The Franck-Condon principle then states that dissociative attachment... 

Inorganic chemistry concerns molecules of all the atoms. The electron affinities of atoms, small molecules, and radicals and their relationship with the Periodic Table, electronegativities of elements, Morse curves of diatomic anions, and the energies of ion molecule reactions and bond energies are inorganic problems we have considered. Ionic radii can be estimated using potential energy curves. 

The simple molecular orbital theory of bonding in homonuclear diatomic molecules can be used to estimate the electron affinities of clusters. In these cases, there can be different geometries. The Cn clusters have been studied most extensively. In the case of the triatomic molecules, there are now two distances and one angle that... 

The theoretical methods for calculating the electron affinities of atoms, diatomic molecules, and polyatomic molecules have been summarized and compared with the CURES-EC method for molecules. The density functional calculations of the electron affinities of substituted benzoquinones and scaled ab initio LUMO agree with the evaluated values for nitrobenzenes. 

The isoelectronic equivalence is the simplest procedure for estimating electron affinities. It was applied to H2 and I2 and to the atomic electron affinities. Species with the same outer electronic configuration should have similar electron affinities and bond dissociation energies. This results in the relative constancy of the electron affinities of a given family of atoms. The equivalence of the bond dissociation energies for the X2( ) and Rg2(+) ions is also based on this principle. The systematic variation of the electron affinities of the homonuclear diatomic molecules is another example. 

In Chapter 8 the electron affinities of atoms were evaluated. In this chapter the electron affinities of diatomic and triatomic molecules and SF (n= 1 to 6) will be considered. The ECD has been used to study CI2, Br2, I2, NO, 02, C02, COS, CS2, N20, N02, SO2, SF6. All the Ea for these molecules have been calculated by the CURES-EC method. The comparison of the relative electron affinities of COS, CS2, and N20 will be illustrated by READS-TCT calculations. 

The homonuclear diatomic molecules are the simplest closed set of molecules. Many of the electron affinities of the main group diatomic molecules have been measured by anion photoelectron spectroscopy (PES), but only a few have been confirmed. These Ea can be examined by their systematic variation in the Periodic Table. Calculating Morse potential energy curves for the anions and comparing them with curves for isoelectronic species confirm experimental values. The homo-nuclear diatomic anions of Group IA, IB, VI, VII, and 3d elements and NO are examined first. 

Electron Affinities and Periodic Trends of Homonuclear Diatomic Molecules... 

The electron affinities of the main group homonuclear diatomic anions have been measured by PES. A few experimental values for the transition metal dimers are also available. The electron affinities of all the 3d homonuclear diatomic molecules have been calculated using density functional methods [1-4], Only the AEa of I2, 2.524 eV C2, 3.27 Si2, 2.2o S2, 1.67 F2, 3.0g Cl2, 2.4s Br2, 2.5, and 02, 1.07 have been measured by more than one method [1-3]. CURES-EC calculations confirm these to within 0.1 eV. Positive excited states Ea have been measured for 02, C2, and I2 and are inferred for other X2 [5-8]. Just as in the case of the atomic Ea, the trends in the Periodic Table can support the assignments of AEa for the other elements. 

Figure 9.1 Electron affinities of the elements, electron affinities, and bond dissociation energies of the homonuclear diatomic molecules in the form of a Periodic Table [1],...

The tables in Appendix IV summarize the evaluated values of the electron affinities given in this book. The electron affinities of the atoms and homonuclear diatomic molecules are given in two tables, Al.l and A1.2. The references for both tables are combined. The electron affinities of the hydrocarbons are given in Tables A2.1 and Al.l. Tables A2.3 and A2.4 provide the electron affinities of the halogenated hydrocarbons. The odd-numbered tables are ordered by value and the even-numbered tables are ordered by molecular weight. The references for the hydrocarbons are given separately from those of the CHX compounds. Tables A3.1 and A3.2 list the values for the CHNX molecules. These were combined because there are so few halogenated compounds. Tables A4.1 and A4.2 contain the electron affinities of the CHO and CHOX compounds, while Tables A5.1 and A5.2 contain those of the CHON and CHONX compounds. 

The electron affinities of the Group II homonuclear diatomic molecules should be greater than the electron affinity of the atom. 

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