Lifetimes of metastable states

Lx>ng radiative lifetimes of metastable states support the high density of these particles in slightly ionized plasma, or in excited gas. Thus, according to Fugal and Pakhomov [18, 19] the density of metastable atoms of helium at pressure of the order of a few Torrs, at temperatures ranging from 4 to 300 K, is about two orders of magnitude above the density of electrons. The density of metastable atoms and molecules in... 

The Editor would like to thank the authors for their contributions, which give an interesting picture of the current range from studies of the use of the Lie algebra in quantum theory, overestimates of the neutrino mass, to relativistic effects in atoms and molecules and the calculation of lifetimes of metastable states by means of the method of complex scaling. 

Thus for H - 0 the free energy barrier AF diverges as H d l which means that the lifetime of metastable states can get very large. Since for a... 

The nuclear decay of radioactive atoms embedded in a host is known to lead to various chemical and physical after effects such as redox processes, bond rupture, and the formation of metastable states [46], A very successful way of investigating such after effects in solid material exploits the Mossbauer effect and has been termed Mossbauer Emission Spectroscopy (MES) or Mossbauer source experiments [47, 48]. For instance, the electron capture (EC) decay of Co to Fe, denoted Co(EC) Fe, in cobalt- or iron-containing compormds has been widely explored. In such MES experiments, the compormd tmder study is usually labeled with Co and then used as the Mossbauer source versus a single-line absorber material such as K4[Fe(CN)6]. The recorded spectrum yields information on the chemical state of the nucleogenic Fe at ca. 10 s, which is approximately the lifetime of the 14.4 keV metastable nuclear state of Fe after nuclear decay. 

In particular, irregular vibrational spectra with Wignerian level spacing statistics have been observed this last decade for a number of highly excited molecules [3-7]. On the other hand, many recent works have characterized the reactive dynamics in terms of quantum resonances, which allows a rigorous definition of metastable states with finite lifetimes and hence of dissociation rates [4, 8-10]. 

Fig. 1. Energy levels of the antiproton in pHe+. The p is captured by replacing one of the Is electrons, which corresponds for the p to a state with principal quantum number no JW /m, where M is the reduced mass of the atomcule, and m the electron mass. About 3% of antiprotons are captured in metastable states (black lines) at high angular momenta L n — 1, for which deexcitation by Auger transitions is much slower than radiative transitions. The lifetimes of these states is in the order of /is. The antiprotons follow predominantly cascades with constant vibration quantum number v = n — L — 1 (black arrows) until they reach an auger-dominated short-lived state. The atomcule then ionizes within < 10 ns and the pHe++ is immediately destroyed in the surrounding helium medium. The overall average lifetime of atomcules is about 3 — 4 ps...

Figure 13. Interferogram of film formed from solution of nonionic detergent (Enordet AE1215-30, 0.052 mol/L). As the film thins, less light is reflected. Formation of metastable states of uniform thickness is revealed by steps . The height of the step corresponds to the thickness of film. The width of the steps is proportional to the lifetimes of respective metastable states. The vertical distance between steps corresponds to micelle diameter, about 10 nm. (Reproduced with permission from reference 54. Copyright 1990 Steinkopff Verlag Darmstadt.)...

Werth, G. Lifetime measurement of metastable states in ions. In Frequency Standards and Metrology, Ed. A. DeMarchi, Springer, Berlin, 1989, 293-299. 

Lifetimes for collision complexes and specific rate coefficients for unimolecular decay of metastable states can be derived in several ways in the framework of the adiabatic channel model, resulting in similar fundamental expressions. The major differences between the various derivations of lifetimes are connected to the physical interpretation. 

Because of this spin selection rule, atoms which get into the lowest triplet state, 2 Si, do not easily revert to the ground 1 state the transition is forbidden by both the orbital and spin selection rules. The lowest triplet state is therefore metastable. In a typical discharge it has a lifetime of the order of 1 ms. 

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