Hydrogen atoms optical spectroscopy

A major advantage of facilities with significantly increased muon fiux would be the possibility to use novel experimental techniques which could not be exploited so far [74] like, e.g. the use of cw lasers for optical spectroscopy or an old muonium approach for a new generation M-M search. Further, a wider class of muonic atoms would be become accessible for precision spectroscopy [75] beyond the already started laser investigations of muonic hydrogen [76]. 

This cosmic spectroscopy method has been extended to study variation of other fundamental parameters. The ratio of the hydrogen atom hyperfme transition frequency to a molecular (CO, CN, CS, HCO+, HCN etc.) rotational frequency is proportional to y = a2gp where gp is the proton magnetic -factor [21]. A new preliminary result here is Ay/y = (—2.4 1.8) X 10-6 about 4 billion light years from us (the average z=0.47). Altogether, we now have 3 independent samples of data two optical samples (see [2,3]) and one radio sample. All 3 samples hint that Aa is negative. 

This work, in its turn, was superseded in the late nineteen fifties and sixties before tunable lasers changed the whole complexion of optical spectroscopy. An account of this period is given in the recently published text The Spectrum of Atomic Hydrogen Advances [48]. 

The rapid progress in recent years in the spectroscopy of the hydrogen atom has renewed pressure for a much better optical frequency standard. This in itself would not be enough to solve the measurement problem. New techniques of comparing optical frequencies are needed. He have developed methods of modulating lasers which can be used for frequency differences in excess of 2THz. 

The Rydberg R Is the best known fundamental constant in physics (precision of about 3x10-1°). It has been measured by various consistent optical spectroscopy experiments performed on atomic hydrogen [x, z, 3], The current precision is in fact limited by the reliability of wavelength measurements in the optical domain (1.6x10 i0). it would be very desirable to Improve further the precision of this measurement. 

This system forms highly ionized so-called Penning mixtures [12,13]. The higher excited states of Hj are partly stable and partly unstable, depending on the quantum numbers of the electron present. The stable excited states have, however, only very shallow minima of the potential curves [14]. That is the reason why no spectrum of Hj is observed for the helium plasma jet. The argon excited neutrals, on the other hand, cannot ionize hydrogen atoms or molecules, but could produce excited H2 molecules, which can be detected by optical emission spectroscopy. 

An important property of EPR spectroscopy is the detailed information provided by the structure of the spectra so that there is higher degree of certainty of correctly identifying the radicals than is the case with optical spectroscopy. Thus, chemically similar radicals that would be expected to have similar UV absorption spectra have completely different EPR spectra. For example, in its reactions with organic molecules, OH can attack at a number of different sites, either to abstract a hydrogen atom from a saturated molecule (see Table 5) or to add to an aromatic ring. Each of the product radicals has a distinctive EPR spectrum, and the relative efficiency with which reaction occurs at each site on the target molecule can be determined from the intensities of the spectra of the various radical products. 

For radiofrequency measurements of the fine structure of hydrogen, on the other hand, the Doppler effect is completely tmimportant, since it is proportional to the frequency which is actually measured. The fine structure intervals are given by frequency differences in optical spectroscopy in radiofrequency spectroscopy they are measured directly. The greater precision of radiofrequency measurements would compel careful investigation of the conditions in a gas discharge if this method were chosen for the excitation of the atoms. In fact, in the radio-frequency experiments which have so far been performed on hydrogen and ionized helium, the method of excitation by electron bombardment has been used. 

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