Alkaline-earths atomic energy levels

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... 

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 alkaline earth atoms, on the other hand, the static core polarization model clearly does not reproduce the energies of the atomic levels, because of the magnitude of the nonadiabatic effects/ Several theories have been formulated for the nonadiabatic effects. For example, the validity of the approach of Eissa and Opik has recently been verified by Vaidyanathan and Shorer by comparing calculated and measured quantum defects ofCa. 

The alkaline earth atoms studied all have a second metastable level ( D) whose internal energy is slightly higher than that of the metastable triplet level [12], For most of the reactions investigated, the reaction yields significant chemiluminescence, (hi fact, for some reactions, e,g, M + CH3Q, all of the observed chemiluminescence arises fiom this source [38]), For Ca and Ba, it was possible to correct for the presence of this reaction by optical pumping depletion of the Id level [38,41]. 

The dimers of Be, Mg and Ca are very weakly bound by the electron correlation effects, at the self-consistent field (SCF) level they are not stable. The binding energy of alkaline earth dimers is only 2-4 times larger than that in Kr2 and Xe2 dimers. Thus, alkaline dimers can be attributed to the van der Waals molecules. The situation is changed in many-atom clusters, even in trimers (Table II). This is evidently a manifestation of the many-body effects. The crucial role of the 3-body forces in the stabilization of the Be clusters was revealed at the SCF level previously [3-5], and more recently was established at the Mpller-Plesset perturbation theory level up to the fourth order (MP4) [6,7]. The study of binding in the Ben clusters [8-10] reveals that the 3-body exchange forces are attractive and give an important contribution to... 

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