Metastable states solid

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. 

Glass, a supercooled liquid, is in a metastable state, that is, an apparently stable condition that may be perturbed by external conditions and undergo unpredictable changes, so that the supercooled liquid may be converted to a solid. When glass is made from a well-balanced mixture of former, modifier, and stabilizer, it is remarkably stable. Environmental changes may,... 

Structural polymorphism has been already reported as a peculiar solid-solid phase transition with a large spectral shift in the cast film of CgAzoCioN+ Br (chapter 4). The type 1 spectrum was thermally transformed to the type VI spectrum and then backed to the type I by the isothermal moisture treatment. The reversible spectral change between the type I and VI is a good experimental evidence of Okuyama s prediction on the molecular packing. Since the type VI state is assumed to be a metastable state, the isothermal phase transition to the type I state is expected to be induced by some external stimuli. Water molecules adsorbed to cast bilayer films might act as an accelerator of the phase transition. 

The fluorescence lifetime of the /2 metastable state of Nd + ions in LaBGeOs (a solid state laser) is 280 /u.s and its quantum efficiency is 0.9. (a) Calculate the radiative and nonradiative rates from this excited state, (b) If the effective phonons responsible for the nonradiative rate have an energy of 1100 cm, use the Dieke diagram to determine the number of emitted effective phonons from the F3/2 excited state, (c) From which three excited states of the Nd + ions in LaBGeOs do you expect the most intense luminescence emissions to be generated ... 

Photoinduced spin-related phenomena are a particularly important field of the solid-state photophysics, because fast spin switching is a prospective basis for applications in the field of spintronics. An illustrative example is the production of the metastable state of the iron propyltetrazole (ptz) complex [Fe(ptz)6](BF4)2 by laser light-induced excited spin-state trapping (LIESST) and the determination of the resulting structure by steady-state X-ray photodiffraction [68]. In another example, steady-state X-ray photodiffraction at cryogenic temperatures was successfully utilized to study photoinduced phase transition due to spin crossover in the tris(a-picolylamine)iron(II) complex [69]. The phase transition is accompanied by... 

RH (e.g., Oatis et al., 1998). In addition, there is evidence that new metastable solid states can form in these droplets (Tang et al., 1995). Similar studies of ammonium bisulfate, NH4HS04, have been carried out over a range of temperatures and relative humidities relevant to the atmosphere, and its phase diagram, including metastable states and a crystalline hydrate phase at low temperatures has been reported (Imre et al, 1997). 

Some pure substances from a glass-like solid, on cooling, rather than a crystalline solid. In such solids the molecules have a certain randomness in their spatial distribution, more like a liquid than a crystal. This is an example in which a metastable state rather than an equilibrium state is obtained on cooling. If such a solid is obtained on cooling to the lowest experimental temperature, then the value of the entropy function at 0 K, obtained on extrapolation, will be greater than zero. 

The second major section will focus on those special centers of minerals thought to be of importance to their catalytic activity, with an emphasis on the known and possible effects of electronic excitation on the population and mode of action of these centers. Metastable states constitute a hidden variable in defective solids, a non-negligible one for non-stoichiometric ones. With regard to concepts of mineral catalysis, the only systems for which extensive spectroscopic information on mineral catalytic centers has been definitively coupled to the mechanism of a well understood surface chemical reaction is exchange on binary oxides. Existing data for the... 

The ratio of the experimental flow J to. /lllM, the decomposition coefficient, may be useful in assessing the decomposition mechanism. However, account must be taken of formation of the solid product in a metastable state. The formation of this material may be the rate-limiting step. Beruto and Searcy3334 have carried out a study of CaC03 decomposition using these principles. They have also studied the nature of the CaO formed. Thus, the field of solid decomposition kinetics seems to be moving toward a detailed examination of the products formed, with less emphasis on the overall kinetic equations. 

Metastable amorphous solids can in general be prepared from stable phases by bringing in excess free energy [5]. In the case of water, amorphous solids have been prepared from stable phases in all three aggregate states from the gas, the liquid, and the crystalline solid [131]. 

Fig. 1. (Left) The structure of the pHe+ atomcule, where the p with large-(n, l) quantum numbers circulates in a localized orbit around the He2+ nucleus, while the electron occupies the distributed Is state. (Right) The level scheme of large-(n, l) states of the pHe+ atomcule. The solid bars indicate radiation-dominated metastable states, while the broken lines are for Auger-dominated short-lived states. The ionized pHe++ states are also shown by dotted lines. From Ref. [2]...

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