An intramolecular theory of the mass-independent isotope effect for ozone. II. Numerical implementation at low pressures using a loose transition state

A theory is described for the variation in the rate constants for formation of different ozone isotopomers from oxygen atoms and molecules at low pressures. The theory is implemented using a simplified description which treats the transition state as loose. The two principal features of the theory are a phase space partitioning of the transition states of the two exit channels after formation of the energetic molecule and a small (ca. 15%) decrease in the effective density of states, rho [a "non-Rice–Ramsperger–Kassel–Marcus (RRKM) effect"], for the symmetric ozone isotopomers [B. C. Hathorn and R. A. Marcus, J. Chem. Phys. 111, 4087 (1999)]. This decrease is in addition to the usual statistical factor of 2 for symmetric molecules. Experimentally, the scrambled systems show a "mass-independent" effect for the enrichments delta (for trace) and E (for heavily) enriched systems, but the ratios of the individual isotopomeric rate constants for unscrambled systems show a strongly mass-dependent behavior. The contrasting behavior of scrambled and unscrambled systems is described theoretically using a "phase space" partitioning factor. In scrambled systems an energetic asymmetric ozone isotopomer is accessed from both entrance channels and, as shown in paper I, the partitioning factor becomes unity throughout. In unscrambled systems, access to an asymmetric ozone is only from one entrance channel, and differences in zero-point energies and other properties, such as the centrifugal potential, determine the relative contributions (the partitioning factors) of the two exit channels to the lifetime of the resulting energetic ozone molecule. They are responsible for the large differences in individual recombination rate constants at low pressures. While the decrease in rho for symmetric systems is attributed to a small non-RRKM effect eta, these calculated results are independent of the exact origin of the decrease. The calculated "mass-independent" enrichments, delta and E, in scrambled systems are relatively insensitive to the transition state (TS), because of the absence of the partitioning factor in their case (for a fixed non-RRKM eta). They are compared with the data at room temperature. Calculated results for the ratios of individual isotopomeric rate constants for the strongly mass-independent behavior for unscrambled systems are quite sensitive to the nature of the TS because of the partitioning effect. The current data are available only at room temperature but the loose TS is valid only at low temperatures. Accordingly, the results calculated for the latter at 140 K represent a prediction, for any given eta. At present, a comparison of the 140 K results can be made only with room temperature data. They show the same trends as, and are in fortuitous agreement, with the data. Work is in progress on a description appropriate for room temperature

An intramolecular theory of the mass-independent isotope effect for ozone. I

An intramolecular theory of the unusual mass-independent isotope effect for ozone formation and dissociation is described. The experiments include the enrichment factor, its dependence on the ambient pressure, the ratio of the formation rates of symmetric and asymmetric ozone isotopomers, the enrichment of ozone formed from heavily enriched oxygen isotopes, the comparison of that enrichment to that when the heavy isotopes are present in trace amounts, the isotopic exchange rate constant, and the large mass-dependent effect when individual rate constants are measured, in contrast with the mass-independent effect observed for scrambled mixtures. To explain the results it is suggested that apart from the usual symmetry number ratio of a factor of 2, the asymmetric ozone isotopomers have a larger density of reactive (coupled) quantum states, compared with that for the symmetric isotopomers (about 10%), due to being more "RRKM-like" (Rice–Ramsperger–Kessel–Marcus): Symmetry restricts the number of intramolecular resonances and coupling terms in the Hamiltonian which are responsible for making the motion increasingly chaotic and, thereby, increasingly statistical. As a result the behavior occurs regardless of whether the nuclei are bosons (16O, 18O) or fermions (17O). Two alternative mechanisms are also considered, one invoking excited electronic states and the other invoking symmetry control in the entrance channel. Arguments against each are given. An expression is given relating the mass-independent rates of the scrambled systems to the mass-dependent rates of the unscrambled ones, and the role played by a partitioning term in the latter is described. Different definitions for the enrichment factor for heavily enriched isotopic systems are also considered. In the present paper attention is focused on setting up theoretical expressions and discussing relationships. They provide a basis for future detailed calculations

Transmission Electron Microscopy of Semiconductor Materials and Devices

This paper surveys the application of transmission electron microscopy (TEM) to semiconductor materials and device technology. A broad spectrum of TEM studies requires the preparation of either plan-view or vertical sections; these sections are made using mechanical abrasion, chemical etching or ion milling or a combination of these procedures. A survey is then given of applications of TEM to four classes of studies of semiconductor materials and devices: the configuration of device features, crystallographic defects, lattice and atomic resolution imaging, and the analysis of phase and chemical composition

Lifetimes and Gj factors in excited states of chromium. Hyperfine structure of Cr53

Electronic and nuclear properties of excited chromium isotopes using level crossing and double resonance spectroscopy technique

Core polarization in chromium-53

Core polarization in chromium 5

Continuous measurements in a composite quantum system and possible exchange of information between its parts

We study an influence of the continuous measurement in a composite quantum system C on the evolution of the states of its parts. It is shown that the character of the evolution (decoherence or recoherence) depends on the type of the measured quantity and on the initial state of the system. A number of conditions under which the states of the subsystems of C decohere during the measuring process are established. We propose a model of the composite system and specify the observable the measurement of which may result in the recoherence of the state of one of the subsystems of C. In the framework of this model we find the optimal regime for the exchange of information between the parts of C during the measurement. The main characteristics of such a process are computed. We propose a scheme of detection of the recoherence under the measurement in a concrete physical experiment.Comment: 6 page

On Kentrodoris and Jorunna (Gastropoda Opisthobranchia)

As 15 espécies anteriormente descritas como Kentrodoris ou Jorunna são revistas. O resultado é que 6 espécies são válidas, 3 já tinham sido removidas para outros gêneros, uma é sinônimo, e 5 não podem com certeza ser colocadas no presente grupo. Por outro lado, descrições pormenorizadas de 3 materiais, identificados com outras espécies, revelam tratar-se de 3 espécies novas, Jorunna alisonae, J. malcolmi e /. zania. Além disso, 2 espécies novas são descritas, J. luisae e J. lemchei. Awuka spazzola revelou-se como Jorunna. A distinção entre Kentrodoris e Jorunna no Tratado de Grassé (Odhner, 1968: 871) baseia-se ainda nas diagnoses de Bergh (1876). Bergh tinha, nas suas espécies, confundido a papila penial inerme e o estilete da glândula vestibular, e descrito o gênero Kentrodoris com estilete penial e glândula vestibular inerme. Em Doris johnstoni (= tomentosa) Alder Hancock (1845) haviam acertadamente reconhecido a papila penial inerme e o estilete da glândula vestibular. Para esta espécie Bergh criou o gênero Jorunna (1876). O meu estudo de 9 espécies, como também boas descrições de 2 espécies ulteriores, mostram que todas as 10 espécies suficientemente conhecidas têm estilete na glândula vestibular e a papila penial inerme. A única espécie com duto masculino cuticularizado é Kendrodoris rubescens. Todas as outras espécies pertencem a Jorunna

On some Opisthobranchs from Cananéia, Brazil

Dez espécies de Cananéia e uma de Ubatuba foram colecionadas. Duas das espécies são novas para a ciência: Coryphella verta e Catriona oba. Elysia serca é comparada com E. clena Marcus (1970, p. 49). Os gêneros Cuthona, Trinchesia, e Catriona são discutidos