Series principal

Whereas the emission spectrum of the hydrogen atom shows only one series, the Balmer series (see Figure 1.1), in the visible region the alkali metals show at least three. The spectra can be excited in a discharge lamp containing a sample of the appropriate metal. One series was called the principal series because it could also be observed in absorption through a column of the vapour. The other two were called sharp and diffuse because of their general appearance. A part of a fourth series, called the fundamental series, can sometimes be observed. 

The result is that the principal series consists of pairs of P /2 S... 

Haupt-satz, m. fundamental principle or law main theorem axiom, -schalter, m. main (or master) switch, -schlagader, /. main artery aorta, -schluss, m. (Elec.) main circuit. -schliissel, m. master key. -schnitt, m. principal section, -schwlngung, /. principal vibration, -serie, /. principal series, -tlcherung,/. (Elec.) main fuse, main cutout. 

Figure 12.7 Electronic transitions giving rise to the emission spectrum of sodium in the visible, as listed in Table 12.1. The principal series consists of transitions from the 3s level to 3p or a higher p orbital the sharp series from 3p to 4s or a higher s orbital diffuse from 3p to 3d or above and the fundamental from 3d to 4/or higher. The terms below the lines [(R/(3-1.37)2, etc.] are the quantum defect corrections referred to in Section 10.4.

There are three principal series of 1,3-oxazinium derivatives with different unsaturation namely, dihydro-1,3-oxazinium 1,1,3-oxazinium 2a,b, and aromatic 3-azapyrylium salts 3 (see Scheme 1). 

Such a radical, when a monad, triad, or pentad, cannot exist os a separate atom like hydrogen or nitrogen, when isolated, it combines with itself, forming a diatomic molecule. It is only by the union of two atoms that the vacated bonds can bo satisfied. Tlie following are two of the principal series of compound... 

In Eq. (1.4) the + sign and constant n describe a sharp series of s states and the minus sign and a constant m describe a principal series of p states. If we consider the special case ds = dp = 0 and m = 2 we arrive at Balmer s formula for the H transitions from n=2. 

When working on line with a mass separator, such as Isolde, the collinear laser spectroscopy is a method fully adapted. In a collaboration Orsay - Mainz, the second members of the principal series in francium have been located and studied at high resolution with this method. In table 1 the measured wavenumbers of the four lines are given. 

Tables 2 and 3 illustrate the principal series of heteropolymolybdates and heteropolytungstates, respectively, which have been reported. Table 4 represents central atoms that form heteropoly anions, the composition and structure of which have not yet been elucidated.

The result is that the principal series consists of pairs of 2/>1/2 —2 S i/2> 2Pj/i 2 1/2 transitions,3 as illustrated in Figure 7.7(a). The pairs are known as simple doublets. The first member of this series in sodium appears in the yellow region of the spectrum with components at 589.592 nm and 588.995 nm called the sodium D lines. 

Dissociation of (CO)5WAs(Me)2N(Me)As(Me)2W(CO)5 (97) under electron impact proceeds by carbonyl ligand loss and As—W bond dissociation leading to two principal series of ions—(CO) WAs2NMej and W(CO) . 

The principal valence of Group IV elements is 4, each element of the group except lead forming its principal series of compounds in the quadrivalent state. Valences of 2 are common, and 3 occasional. The quadrivalent halogen compounds of most of the elements form characteristic double derivatives with the alkali halides, of the type M12MlTX. These compounds, especially the fluorides, are of much importance. 

In the hydrogen and alkali spectra, as we have already explained for the simple Bohr theory (fig. 13, p. 112 fig. 8, p. 148), the lines which correspond to transitions from a p-term to the ground state (s-term) are called the lines of the principal scries a principal series of higher order contains the lines which lead to the next. s-teim (in our diagram to the 2,s-term). Transitions from the rZ-torrns to the jP-terms give the diffuse series, those from the 5 terms to the ji -terms... 

Fig. 2.2. Example of a long Rydberg series for a many-electron atom the principal series of Sr (after M.A. Baig and J.-P. Connerade [24]).

The fitting of Rydberg series to high resolution data, when performed with sufficient accuracy, can reveal very fine details of atomic spectra. Thus, by carefully fitting the principal series of T , the influence of hy-perfine structure on the determination of the ionisation potential has been revealed [32]. 

Fig. 4.2. Plot of the differential oscillator strength df/dE as a function of energy for the principal series of Na (experimental data) each box represents one transition, arranged (see the previous figure) so that the df/dE graph has no gaps. A smooth curve then connects the points shown, and should, in this example, tend to a straight line. Since the measurements were made in the presence of a magnetic field, the very high Rydberg members appear to lose intensity because satellite lines emerge, as explained in chapter 10 (after M. Nawaz et al [166]).

Fig. 4.3. The principal series of Ba I in the vicinity of the first ionisation threshold, showing how the df/dE curve of the high series members joins smoothly onto that of the continuum, even in the presence of a strong perturber, in this case a doubly excited resonance straddling the threshold, which has a pronounced effect on the course of intensities (see fig. 8.22 - after J.-P. Connerade et al [136]).

Typical results of / value determinations are illustrated here by two examples. The first relates to the principal series of Sr in a synchrotron radiation experiment, while the second relates to / value determinations for the principal series of Ba obtained in a laser-based experiment. Full descriptions of the experimental details for both synchrotron [163] and laser[164]-based MOV experiments have been published. The data are summarised as df/dE curves, which were introduced in section 4.6. 

---