Rydberg measurement

Precision spectroscopy of helium has not, in general, been of importance for fundamental constants with the single conspicuous exception of optical spectroscopy of ionized helium. Taking advantage of the zero spin nucleus, E. Kessler was able to accomplish the last definitive Rydberg measurement before the advent of Doppler-free spectroscopy [20]. Beyond this, when two electrons are present, the physical constants and the QED effects are joined by the problem of how the two electrons learn to live with one another. This subject is rich and diverse and is treated to some extent in the contribution of Professor Fano to this Conference. 

A term that is nearly synonymous with complex numbers or functions is their phase. The rising preoccupation with the wave function phase in the last few decades is beyond doubt, to the extent that the importance of phases has of late become comparable to that of the moduli. (We use Dirac s terminology [7], which writes a wave function by a set of coefficients, the amplitudes, each expressible in terms of its absolute value, its modulus, and its phase. ) There is a related growth of literatm e on interference effects, associated with Aharonov-Bohm and Berry phases [8-14], In parallel, one has witnessed in recent years a trend to construct selectively and to manipulate wave functions. The necessary techifiques to achieve these are also anchored in the phases of the wave function components. This bend is manifest in such diverse areas as coherent or squeezed states [15,16], elecbon bansport in mesoscopic systems [17], sculpting of Rydberg-atom wavepackets [18,19], repeated and nondemolition quantum measurements [20], wavepacket collapse [21], and quantum computations [22,23], Experimentally, the determination of phases frequently utilizes measurement of Ramsey fringes [24] or similar" methods [25]. 

The combined experimental and theoretical investigation of Dixon et al. [75] applied the H-atom Rydberg time-of-flight method to measure the translational energy distribution of H atoms from the photodissociation... 

If we suppose that these Rydberg states have non-negligible lifetimes against autoionization, as could occur via dispersion of the potential energy of the molecule into various vibrational modes, then these states would be very sensitive to electric fields in the measuring apparatus. It is suggested here that this is the reason for the large discrepancies between cross sections measured in the various beam experiments. 

The physical nature of the ZEKE states has been the subject of intense experimental and theoretical investigation in the past several years. In the well-studied case of NO,14,21 we know from the 3 cm-1 red shift of the ZEKE-PFI threshold band relative to the true adiabatic ionization potential (extrapolated from highly accurate measurements of Rydberg series) that the ZEKE states have principal quantum number n 200 and lifetime of 2 (is or longer. Recent work has found ZEKE states with lifetimes as long as 20 ps.22... 

Rydberg series were detected in molecular spectra in the early 1930 s, notably by W. C. Price who showed that they arose from the outer electrons. These can usually be fairly well classified in terms of the structure of the molecule, e.g. non-bonding electrons on particular atoms or electrons of double bond systems. Non-bonding electrons give more nearly atomic Rydberg series, with many numbers observable, and correspondingly accurate ionization potentials have been recorded. Most of the earlier measurements belong to this class. 

Several methods have been employed to measure the energy of this state in nonpolar liquids. The methods fall into three categories the change in work function of a metal when immersed in the liquid, photoionization, and field ionization. Of these, the latter, in which field ionization of high-lying Rydberg states is utilized to locate Fq, has in recent years provided what are considered to be the most accurate values of Fq in fluid Ar, Kr, and Xe. 

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