Term scheme

FIGURE 5.16 Crystal-field pictures for the low-spin d5 system in deformed octahedra. (a) relative energy of d-orbitals for an octahedron with strong crystal field (b) d-orbitals of the T2s set in a rhombically distorted octahedron (c) three possible electron configurations of increasing total energy (d) the term scheme for the configurations in (c). 

Fig. 4.9. Term scheme for He I, showing some of the transitions of interest.

The redox potential of this regenerating couple has to be either more negative than the oxidative redox potential of the dye (° d/d+) in the case of electron injection from >, or more positive than the reductive redox potential (°Ed/d ) in the case of hole injection from D. A simple term scheme" of such a charge injection with regeneration of the reaction products is given in Fig. 18. Such a... 

There is another possible mechanism which really deserves the name supersensitization because the charge injection becomes either only just possible or is largely increased by the interaction between dye molecule and supersensitizer. This is the case if the excited dye molecule reacts at first with the supersensitizer and reaches in this way a state where it can inject an electric charge even in the ground state. The "term scheme for this mechanism is shown in Fig. 20. The assumption here is that the excited state of the molecule as a donor cannot inject an electron into the conduction band or can do this only very ineffectively. It can, however, act as an electron acceptor against the supersensitizer. 

Fig. 3.32. Rotovibrational term scheme of H2 showing single and double transitions of pairs after [187],...

Overtone bands. The induced first overtone band of H2 is shown in Fig. 3.37 at a variety of temperatures, observed in pure hydrogen gas using long absorption paths. Instead of the three components Q, S(0) and S(l) seen in the fundamental band, we now observe much richer structures, especially at the lower temperatures. This fact suggests that a number of double transitions take place. If one constructs a rotovibrational term scheme of the H2 molecule, like Fig. 3.32, which includes the lowest rotational levels of the v = 2 vibrational state, this is obvious. Various... 

In later years much important work was carried out in the St. Andrews laboratories on anhydro-sugars and their derivatives (G. J. Robertson) and on the nitrate esters of methylated sugars (J. W. H. Oldham). Irvine never diminished his keen interest in this work but it was inevitable that less time could be devoted to chemical research after he had assumed the onerous duties of Principal and Vice-Chancellor in 1921. It was characteristic of him, however, that only a few days before his death he was busy propounding long-term schemes of research on possible developments of sugar derivatives for use in chemotherapy. 

With fixed [CO], and increasing [02] the steady-state reaction rate W is initially zero (the overall surface is covered with CO) and it can then jump to the value k22[CO]212kt [02]. With further increase in [02], the reaction rate varies inversely with [02]. In turn, with constant [02] the reaction rate rises quadratically with increasing [CO] and then "jumps down to zero values. This example indicates that rather simple but non-linear schemes can be characterized by complex dynamic behaviour. In radiophysical terms, scheme (119) can be called a simple catalytic trigger since, in this case, there exist two stable steady states. 

Fig. 3. (a) Term schemes of an 5 = spin system. Heavy arrows indicate EPR transitions with... 

The term schemes of the elements are well documented in the work of Grotrian [3]. For the case of the Na atom the term scheme is represented in Fig. 1. 

When atoms have more than one valence electron, the term schemes become more complex as a coupling between the impulse and orbital momentums of the individual electrons occurs. According to Russell and Saunders (L — S) a coupling applies, where the orbital moments of all electrons have to be coupled to a total orbital momentum, as with the spin momentum. This coupling applies for elements with Z below 20, where it is accepted that the spin-orbital interactions are much lower than the spin-spin and the orbital-orbital interactions. The fact that none of the electrons in an atom can have the same set of quantum numbers is known as the Pauli rule. The total quantum number I is obtained as L = 2,1, S = Es and J = L — S,..., I + S. The term symbol accordingly becomes ... 

Fig. 6. Term schemes for (a) atomic emission, (b) absorption and (c) fluorescence spectrometry (resonant hv and non-resonant hv ).

In order to obtain the optimum power of detection, the analyte density in the plasma, the ionization and the ion transmission must be maximized. The power will thus be between 0.6 and 2 kW and the sampler at about 10-15 mm above the tip of the injector. The detection limits, obtained at single element optimum conditions differ considerably from those at compromise conditions, but are still significantly lower than in ICP-AES (Table 17). In general it can be said that for the heavy elements, which have complex atomic term schemes and accordingly very... 

In atomic spectroscopy the term values depend primarily on electronic quantum numbers and the process of analysis consists of reducing a number of measurements to a term scheme. The confidence in an analysis increases as the system becomes more overdetermined, and the process becomes more definite as the accuracy of the measurements improves. Other information is also used to facilitate the assignments of the lines, e.g., relative intensities, the observation of certain lines in absorption, the splittings of lines by magnetic fields theoretical calculations of terms and multiplet splittings may sometimes be helpful. 

If we know the term scheme for an atom, we can at once read off from it the structure of the spectrum. For the hydrogen atom the term scheme has the form... 

This expression for the value of the energy is called the Deslandres term. To this term scheme there corresponds a definite [Pg.100]

Fig. 13,—Term scheme of sodium (with not too high resolution). The transitions between the various levels give the emission lines.

Fig. 15.—Term scheme of X-ray levels (after Kossel), with the transitions corresponding to the X-ray lines.

The case of hydrogen is peculiar in one respect. Experiment gives distinctly fewer terms than are specified in the term scheme of fig. 8 for = 2 only two terms are found, for n = 3 only three, and so on. The theoretical calculation shows that here (by a mathematical coincidence, so to speak) two terms sometimes coincide, the reason being that the relativity and spin corrections partly compensate each other. It is found that terms with the same inner quantum number j but different azimuthal quantum numbers I always strictly coincide, for instance, the ns and the np, term, the p. , and the d, term, and so on such pairs of terms are drawn close together in fig. 8. For the value of the terms a formula was given by Sommerfeld (1916), even before the introduction of wave mechanics the same formula is also obtained when the hydrogen atom is calculated by Dirac s relativistic (E908) 11... 

Fig. Q.—Term scheme for sodium, taking account of spin on the left are shown the energies of the terms in electron volts (measured from the ground state) on the right the frequencies (in wave numbers) which are emitted at a transition downwards from the series limit, and also the values, of V Rli>).

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