Alkaline-earth atoms

A systematic analysis of autoionization electron spectra due to collisions of electrons on alkaline earth atoms has again been performed by Ross and co-workers (see also references therein for other investigations). 

Regarding core-excited states most of them are still unidentified. Only for core-excited Be, which was studied in detail by R0dbro et could a 

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Beams of metal atoms have been prepared by many researchers tlirough thennal vaporization from a heated cmcible. An example of such a source, employed for the generation of beams of alkaline earth atoms, is described by Irvin and Dagdigian [H]. By striking an electrical discharge within this source, beams... 

In the alkaline earth atom ease, the polarized orbital pairs are formed by mixing the ns and np orbitals (aetually, one must mix in equal amounts of pi, p.i, and po orbitals to preserve overall S symmetry in this ease), and give rise to angular eorrelation of the eleetron pair. Use of an (n+l)s2 CSF for the alkaline earth ealeulation would eontribute in-out or radial eorrelation beeause, in this ease, the polarized orbital pair formed from the ns and (n+l)s orbitals would be radially polarized. 

The splitting of triplet terms of helium is unusual in two respects. First, multiplets may be inverted and, second, the splittings of the multiplet components do not obey the splitting rule of Equation (7.20). For this reason we shall discuss fine stmcture due to spin-orbit coupling in the context of the alkaline earth atomic spectra where multiplets are usually normal and... 

II. TRENDS IN INTERATOMIC DISTANCES NEAREST NEIGHBOR DISTANCE (Angstroms) ALKALINE EARTH ATOMIC SIZE... 

We see that, no matter what type of bonding situation is considered, there is a trend in size moving downward in the periodic table. The alkaline earth atoms become larger in the sequence Be < Mg < Ca < Sr < Ba. These atomic sizes provide a basis for explaining trends in many properties of the alkaline earth elements and their compounds. 

From Exercise 21-4 we see that the decreasing ionization energies observed for the alkaline earth atoms are readily explained in terms of their increasing size moving down in the periodic table. Notice that the ionization energy trend going down in the periodic table is the same as the trend going to the left in the periodic table. 

Fig. 21-1. Sizes of the alkaline earth atoms with various bond types (in Angstroms)...

Such phenomena do not occur in heavier alkaline earth atoms due to a poorer differential overlap between the valence s and p orbitals (smaller Ksp integrals) as explained by... 

Relativistic ANO Type Basis Sets for the Alkaline and Alkaline Earth Atoms Applied to the Ground State Potentials for the Corresponding Dimers. 

Fig. 2.4-10. High coordination number (CN) polyhedra around alkali (alkaline earth) atoms in different mercu7 rich amalgams and in BaCdn (a) CN 15 and (b) CN 16 around K in...

Both alkali metal and alkaline earth atoms are reactive with oxygen-bearing terminal groups but the latter appear to be far more destructive. K deposition on -COOCH3 and -COOH terminated SAMs results in a 1 1 reaction to form -COO species, which in the ester case requires cleavage of the -CH3 group [45, 46, 58, 59, 61]. Walker and co-workers have reported that Ca deposition on OCH3... 

In all of these crystals the ratio of number of oxygen atoms to number of aluminum atoms and silicon atoms is 2 1, as required for a complete tetrahedral framework, and the number of alkali and alkaline-earth atoms is that required by the argument given above. (In a few cases, such as sodalite, described below, more alkali ion is present, balanced by halogenide ion or a similar anion.)... 

In most optical excitations the resolution is determined by the Doppler effect or the finite linewidth of the light source. The Doppler effect gives a typical frequency width of 1 GHz, and the width of the light source can be anywhere from 1 kHz to 30 GHz. We assume that these widths are larger than the radiative width. The photoionization cross sections from the ground states of H, alkali, and the alkaline earth atoms are given in Table 3.3. 20... 

Purely optical excitation is possible for alkali and alkaline earth atoms. For most other atoms the transition from the ground state to any other level is at too short a wavelength to be useful. To produce Rydberg states of such atoms a combination of collisional and optical excitation is quite effective. A good example is the study of the Rydberg states of Xe by Stebbings et al.24 As shown in Fig. 3.5, a thermal beam of Xe atoms is excited by electron impact, and a reasonable fraction of the excited atoms is left in the metastable state. Downstream from the electron excitation the atoms in the metastable state are excited to a Rydberg state by pulsed dye laser excitation. 

In this chapter we have implicitly assumed the Rydberg atom to be a one electron-atom. In the perturbed Rydberg series of, for example, alkaline earth atoms, Rydberg states can have mixed valence-Rydberg character. In such states the black body effects are reduced by a factor equal to the fractional Rydberg character.14... 

A good illustration of the contribution of inelastic collisions to the broadening cross sections is provided by the alkaline earth atoms, which have perturbations in... 

For simplicity we shall consider the Ba atom, although precisely the same procedure could be carried out for any alkaline earth atom. We shall assume that Ba consists of an inert spherical closed shell Ba2+ core which has two electrons.3 The basic notion of the treatment of Van Vleck and Whitelaw2 is readily understood by looking at the energy level diagram of Fig. 17.1. Each one electron... 

Three different methods have been used to make microwave resonance measurements of intervals between alkaline earth Rydberg states. In all of these measurements state selective laser excitation of alkaline earth atoms in a beam was combined with one of three forms of state selective ionization of the final states. 

While the agreement of the measured and calculated Ba+ quadrupole polarizabilities is not very good, compared to an analysis based on adiabatic core polarization the agreement in Table 17.3 is superb. The adiabatic core polarization model leads to ad = 146flo and aq = —5800. The ground state of Ba+ cannot have a negative quadrupole polarizability. Taken together, the Ca and Ba experiments show clearly that the nonadiabatic effects in core polarization in the alkaline earth atoms are important and may be calculated with some accuracy. 

A laser method which has been used to study autoionizing states of alkaline earth atoms is the isolated core excitation (ICE) method first used by Cooke etal. to study the autoionizing 5pn( states of Sr.11 It has since been used to study autoionizing states of Mg, Ca, and Ba as well.12-14... 

Fig. 22.1 (a) Experimental setup for three laser excitation of atomic vapors with ionization detection and reference signal for calibration, (b) Energy level diagram of a typical alkaline earth atom showing the sequence which allows easy excitation of T° states (from ref. 1). 

In looking for other trends in the data of Figure 6.6, the near-zero Eea s of the alkaline earth metals (Be, Mg, Ca, Sr, Ba) are particularly striking. Atoms of these elements have filled s subshells, which means that the additional electron must go into a p subshell. The higher energy of the p subshell, together with a relatively low Zeff for elements on the left side of the periodic table, means that alkaline earth atoms accept an electron reluctantly and have Eea values near zero. 

Let us first consider a simple Auger process with only a single decay channel [Nc = 1, see Eq. (4)]. Although not characteristic of K-shell Auger, such processes take place upon (n - l)p ionization of alkaline earth atoms, for example, in (2p 1) Mg+, where the only nonradiative decay pathway involves the two 3s electrons (2p-1) Mg+ (3s-2) Mg2+ + e. Assume that... 

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