Helium, spectrum

There is also a temperature effect. Generally at low temperatures (liquid nitrogen or even liquid helium), spectra will show more detail with regard to magnetic properties and are easier to obtain. For the nuclei of many elements, spectra are obtainable only at low temperatures if at all. 

FIGURE 2 The proton and helium spectra at low energy. [From Suzuki, T, ef al. (2000). Precise measurements of cosmic-ray proton and helium spectra with BESS spectrometer, Astrophys. J. 545,1135-1142 The AMS Collaboration. (2000). Protons in near earth orbit, Phys. Lett. 5472, 215-226 The AMS Collaboration. (2000). Helium in near earth orbit, Phys. Lett. 5494, 193-202.]... 

Figure 3. Contour piot of the eiectronic density of a (tripiet) eigenstate strongly scarred by the antisymmetric stretch orbit (left), in 2D configuration space (spanned by the electrons distances ri and r-2 from the nucleus, in the collinear configurations considered here). This eigenstate belong to the N = 9 series. The solid lines depict the associated classical periodic orbit. Autoionization rates of antisymmetric stretch singlet states (right) of the Nth autoionizing series of the helium spectrum, in ID (squares), 2D (circles), and 3D (diamonds) configuration space.

The helium spectrum of the WN5 star HD 50896 (EZ Canis Majoris, WR6) is studied. Our aim is to establish a technique which allows the determination of the parameters of a Wolf-Rayet star from a systematic analysis of its spectral lines. Since the method of "iteration with approximate Lambda operators" became available for application to expanding atmospheres (Hamann, 1986, 1987), we are now able to compare observed... 

The focus of this chapter is not on the accurate computation of helium energy levels, but on the development of a global understanding of the different dynamical regimes of the helium atom, and on identifying them in the helium spectrum. 

Closer inspection of Fig. 10.8 reveals that the first three m series are completely isolated, i.e. the resonances with different m quantum numbers are energetically well separated from each other. But Fig. 10.8 (d) shows that the lowest state of the fifth series intrudes into the fourth series. The higher series are characterized by more and more intruder states. Thus, as conjectured in Section 10.1 on the basis of the simple independent-particle He -f e model, it is the onset of overlapping series with the accompanying intruder states that, on the quantum level, are the source of complicated behaviour in the helium spectrum. 

One of the most basic features of the helium spectrum is its organization into an infinite sequence of ionization thresholds. This feature is not the result of intricate computations. It is already apparent on the level of the independent particle model of the helium atom (see Section 10.1). All predictions on the quantum manifestations of chaos have to... 

We add a few remarks on the wave mechanics of many-body problems, Here of course we are concerned with the solution of a wave equation in many-dimensional space thus the calculation of the helium spectrum needs as many as six co-ordinates, and that of the lithium spectrum nine. It is clear that in these cases an exact solution is not to be looked for, so that we must be content with an approximate solution of the problem. The methods of a highly developed perturbation theory enable us to push this approximation as far as we please the labour involved, however, increases without limit with the order of the approximation. The lowest terms of He, Li+ and Li have already been successfully calculated by this method, with results in good agreement with experiment (Hylleraas, 1930). 

The function for an atomic system must, in order that the Pauli principle shall hold good, possess a character of antisymmetry, changing its sign when the coordinates of two electrons are interchanged. This principle, though abstract, is unambiguously related to very definite experimental facts, such as the character of the helium spectrum, and the specific heat relations of hydrogen. 

A less grandiose but more specific verification of the principle comes from the study of the helium spectrum. This contains two sets of terms which do not combine. So completely independent are they that at one time they were ascribed to two modifications, known respectively as ortho-helium and para-helium. The para terms are singlet and the ortho terms triplet. The normal or ground state of the atom belongs to the para system. This state of affairs first becomes explicable in terms of the symmetry of the wave functions. 

Having constructed the map, a Geissler vacuum tube (preferably an end-on tube, p. loo), containing hydrogen or helium, is fixed before the slit, and connected with the secondary of an induction coil. The chief lines in the case of the hydrogen spectrum are a red line (C line), a blue line (F line), and a violet line while the chief lines in the helium spectrum are two red lines, a yellow line, two green lines, a blue line, and a violet line. The wave-lengths of the most important lines are as follows —... 

The molecular constants that describe the stnicture of a molecule can be measured using many optical teclmiques described in section A3.5.1 as long as the resolution is sufficient to separate the rovibrational states [110. 111 and 112]. Absorption spectroscopy is difficult with ions in the gas phase, hence many ion species have been first studied by matrix isolation methods [113], in which the IR spectrum is observed for ions trapped witliin a frozen noble gas on a liquid-helium cooled surface. The measured frequencies may be shifted as much as 1 % from gas phase values because of the weak interaction witli the matrix. 

Figure Bl.24.10. Random and aligned (chaimelled) backscattering spectrum from a single crystal sample of silicon. The aligned spectrum has a peak at the high energy end of the Si signal. This peak represents helium...

Gr. helios, the sun). Janssen obtained the first evidence of helium during the solar eclipse of 1868 when he detected a new line in the solar spectrum. Lockyer and Frankland suggested the name helium for the new element. In 1895 Ramsay discovered helium in the uranium mineral clevite while it was independently discovered in cleveite by the Swedish chemists Cleve and Langlet at about the same time. Rutherford and Royds in 1907 demonstrated that alpha particles are helium nuclei. 

Solid covalent dinitrogen pentoxide can be prepared by freezing the vapour with liquid helium. Normally, solid dinitrogen pentoxide exists as (NO2+) (NOj ), showing absorption bands in its Raman spectrum only at 1050 and 1400 cm the structure of this form has been determined by X-ray crystallography. ... 

The latter rule is rigidly obeyed in the observed spectrum of helium. From the accurately known energy levels it is known precisely where to look for transitions between singlet and triplet states but none has been found. 

Helium-ion induced X-ray spectrum from anodized tantalum (fluencei 1.5 X 10 HeVcmV ... 

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