Metastable species

Enols of simple ketones can be generated in high concentration as metastable species by special techniques. Vinyl alcohol, the enol of acetaldehyde, can be generated by very careful hydrolysis of any of several ortho ester derivatives in which the group RC02 is acetate acid or a chlorinated acetate acid. ... 

The F + H2 — HF + FI reaction is one of the most studied chemical reactions in science, and interest in this reaction dates back to the discovery of the chemical laser.79 In the early 1970s, a collinear quantum scattering treatment of the reaction predicted the existence of isolated resonances.80 Subsequent theoretical investigations, using various dynamical approximations on several different potential energy surfaces (PESs), essentially all confirmed this prediction. The term resonance in this context refers to a transient metastable species produced as the reaction occurs. Transient intermediates are well known in many kinds of atomic and molecular processes, as well as in nuclear and particle physics.81 What makes reactive resonances unique is that they are not necessarily associated with trapping... 

The metastable species involved in these reactions may be either excited charge-transfer complexes or biradicals, although a charge-transfer complex would be expected to result in a predominance of head-to-head dimers. Dipole effects, on the other hand, would favor formation of head-to-tail dimers, especially in relatively nonpolar solvents ... 

TABLE 5.1 Excitation Energy of Metastable Species and Internal Energy of a Typical M+... 

A second successful prediction is that many so-called metastable species (i.e. isomers) are abundant even if they are quite reactive in the laboratory.66 Perhaps the simplest interstellar molecule in this class is HNC, but large numbers of others can be seen in Table 1. It is assumed that most metastable species are formed in dissociative recombination reactions along with their stable counterparts at approximately equal rates, and that both are destroyed by ion-molecule reactions so that the laboratory reactivity, which is normally determined by reactions with neutral species, is irrelevant. Both HCN and HNC, for example, are thought to derive from the dissociative recombination reaction involving a linear precursor ion ... 

The formation of bulk cobalt carbide is quite a slow process since it requires the diffusion of carbon into the cobalt bulk. It was reported that the full conversion of unsupported and reduced Co to Co2C only occurred after 500 h of exposure to pure CO at 230°C. Increasing the reaction temperature resulted in a faster rate of carburization.81 Bulk cobalt carbides are considered to be thermodynamically metastable species, and therefore Co2C will decompose to hep cobalt and graphite, while Co3C will decompose to fee cobalt and methane. Thermal decomposition of bulk carbides under an inert atmosphere is believed to occur at 400°C.81 Hydrogenation of the bulk carbides is believed to be a fast process and occurs around 200°C.82 83... 

To summarize, from literature there does not seem to be much consensus on whether bulk cobalt carbide forms during realistic FTS conditions. Bulk carbide is generally considered a metastable species. However, it is clear that it may form under upset conditions. Furthermore, there is strong evidence to show that if bulk cobalt carbide is present, it is deleterious in terms of both catalyst activity and selectivity. With this in mind, it would be prudent to operate the catalyst in a regime (sufficiently high H2/CO ratio) where bulk carbide formation is avoided. 

Photolysis of DAX in a methylcyclohexane glass at 77 K creates a metastable species detected by its optical absorption spectrum (Table 4). This solution does not exhibit an epr spectrum characteristic of a triplet carbene, nor is one observed when DAX is irradiated in Fluorolube (where triplet carbenes are generally more stable). Warming the frozen solution causes the reaction of the metastable transient and the formation of dimeric xanthone azine. 

Thus, in these two examples the most stable species in solution is not that found in die crystal. The long lifetimes of the metastable species in solution at low temperatures may indicate that the dissolution process leads initially to polymolecular aggregates in which the intermolecular hydrogen bonds are maintained. 

This reaction is slow, but could build up in supply. Ozone (03) is the metastable species in the process (like H02 in H2—02 explosions) and could initiate... 

Pritzker, M. D. and Yoon, R. H., 1984a. Thermodynamic calculations on sulphide flotation systems I. galena-ethyl xanthate system in the absence of metastable species. Inter. J. Miner. Process, 12 95 - 125... 

Homogeneous gas-phase collisions represent the manner in which reactive free radicals, metastable species, and/or ions are generated. As shown in Table I, electron impact can result in a number of different reactions (27-25). 

The reason for the lack of progress on this allotrope, which was first reported in 1939, and on which over a dozen publications have appeared, is often misunderstood. The difficulty is intrinsic. The existence of a great variety of intramolecular and intermolecular allotropes proves that many species must have comparable stability, i.e., that they can coexist. Thus, many contradictory allotropes are mixtures. We know now that the challenge of preparing and identifying a new allotrope does not end with its sjmthesis, but includes isolation of the metastable species from a mixture of equally metastable compounds, a process that... 

Naumov P, Yu P, Sakurai K (2008) Electronic tera-order stabilization of photoinduced metastable species structure of the photochromic product of spiropyran determined with in situ single crystal X-ray photodiffraction. J Phys Chem A 112 5810-5814... 

Bombardment of solid surfaces with electrons can cause desorption of ground-state neutrals (both atoms and molecules), ions, and metastable species. In addition, dissociation of adsorbed molecules with the resulting fragments remaining attached to the surface can be induced by electron bombardment. Conversion of one bonding mode to another can also occur. 

Heteromolecular -complexes of aromatic cation radicals have been designed from the complexation of aromatic cation radical with a different neutral aromatic donor but such ionic K-heterocomplexes were observed as metastable species in the gas phase or in freon matrices57 58. 

Furthermore, excited metastable species such as Ar11 ICP source due to ... 

Threshold electron spectroscopy, or its newest variant ZEKE spectroscopy, represents a new approach to these problems that has already afforded a broad set of new applications, particularly for soft bonds and metastable species, such as is characteristic for metastable reactive intermediates. 

Zero electron kinetic energy spectroscopy provides a new tool in the study of chemical systems. In particular, it is applicable to molecules that are not in a bottle (metastable species) which nevertheless are of fundamental... 

The second problem concerns the method of sampling to the mass spectrometer. A mass spectrometer operates at pressures not much greater than 10 5 mm Hg, while reactions in flow systems tend to be carried out in the pressure range 10"1 to 10 mm Hg. Capillary leak inlet systems are not particularly suitable for metastable species, since considerable quenching may occur on the walls of the capillary and the sample reaching the... 

The electron capture detector is the result of a series of developments which were initiated in 1951 by D. J. Pompeo and J. W. Otvos (14) of the Shell Company s development laboratory in California. The device they invented was a beta-ray ionization cross-section detector (Section 5.8). Deal et al. (15) at the Shell laboratory in California and Boer (16) in Amsterdam modified the detector, used originally to monitor effluents of a large scale plant process, for applications in GC. From the limited success of the detector. Lovelock (17) produced the beta-ray argon detector in 1958 (Section 5.8). This modification substituted argon as the carrier gas and placed a potential of 1000 V across the electrodes. Argon passing between the electrodes absorbed radiation and formed a metastable species with energy (11.6 eV) sufficient to ionize most substances. Proposed mechanisms for this process are ... 

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