Szénplazmák spektroszkópiai vizsgálata lézerkemencében, különös tekintettel a C3 gyök emissziós spektroszkópiai jellemzésére. = Spectroscopic analysis of carbon plasmas in a laser oven with special emphasis on the emission spectroscopic characterization of the C3 radical

A témában eredeti célkitűzésünk lézerrel gerjesztett szénplazmák megfigyelése és analizise volt szén-nanocsövek lézeres szintézise során, különös tekintettel a C3 molekulagyökre. Ennek során a grafitkemence részbeni megépitése megtörtént,de a támogatás összege (amit az eredeti költségvetéshez képest 1 millió Ft-tal csökkentve kaptunk) a teljes konfiguráció megvalósitásához nem volt elegendő. A meglevő kisérleti konfiguráció azonban, egy esetleges további pályázatban, kiegészithető működő konfigurációvá. Igy a pályázatban plazmaküvetta felhasználásával folytak a kisérletek, a korábbi OTKA Műszerpályázatból beszerzett időátlagoló spektrométer és egy OMFB pályázatból beszerzett Nd: YAG lézer felhasználásával. Eredeményeink továbbhaladást jelentenek lézerrel keltett szénplazmák spektroszkópiai analizisében, különösen a C3 gyök emissziós spektroszkópiai viselkedését illetően. Megfigyeléseink alapján valószinűsithetők azok a fizikai körülmények, amelyek között a C3 400 nm-es emissziós kontinuuma megfigyelhető lézerrel gerjesztett plazmákban. A tervezett nemzetközi kooperációhoz képest változások voltak, mert a portugál fél tematikai változtatást hajtott végre, igy kisérletes felszerelése nem épült fel, és nem látogatott Magyarországra.Eredményeink alapján lehetőség nyilik időfelbontásos spektroszkópiai mérésekkel a C3 gyök plazmakimutatására és kémiai és fizikai jellemzésére. Az ehhez szükséges berendezést a témavezető elnyerte egy 2004 évi GVOP KMA pályázaton. | Our original purpose was to observe and analyze laser induced carbon plasmas during a laser synthesis of carbon nanotubes, with special emphasis on the C3 radical. A partial construction of the laser oven has been realized but the project budget (reduced by 1 million HUF relative to the orginal plan) has not been enough to finalize the set-up. The available set-up can, however, be further developed in a later project into a working laser graphite oven. Thus our experiments have been carried out in a plasma cuvette, using a time averaging miniature spectrometer (won in an earlier OTKA project) and a Nd: YAG pulsed laser (obtained via an OMFB project). Our results represent an advancement in the spectral analysis of laser induced carbon plasmas, especially regarding the spectral behaviour of the C3 radical. Based on our observations one can establish the physical conditions under which the 400 nm continuum of the C3 radical may be detected in laser induced plasmas. There have been changes int he planned international cooperation, as the Portuguese partners changed their research orientation, thus their experimental apparatus has not been constructed and no visit to Hungary has occurred. Nonetheless based upon our results it becomes possible to detect the C3 radical in plasmas by time resolved spectroscopy, and to characterize it chemically and physically. The necessary equipment was procured from a GVOP KMA project of the present project leader

A novel samarium(II) complex bearing a dianionic bis(phenolate) cyclam ligand: synthesis, structure and electron-transfer reactions

A novel divalent samarium complex anchored on a dianionic bis(phenolate) ligand is reported and reactivity studies demonstrate that it is highly effective in inducing single-electron transfer processes.</p

Gas-Phase Reactions of Doubly Charged Lanthanide Cations with Alkanes and Alkenes. Trends in Metal(2+) Reactivity

The gas-phase reactivity of doubly-charged lanthanide cations, Ln2+ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), with alkanes (methane, ethane, propane, n-butane) and alkenes (ethene, propene, 1-butene) was studied by Fourier transform ion cyclotron resonance mass spectrometry. The reaction products consisted of different combinations of doubly-charged organometallic ions?adducts or species formed via metal-ion-induced hydrogen, dihydrogen, alkyl, or alkane eliminations from the hydrocarbons?and singly-charged ions that resulted from electron, hydride, or methide transfers from the hydrocarbons to the metal ions. The only lanthanide cations capable of activating the hydrocarbons to form doubly-charged organometallic ions were La2+, Ce2+, Gd2+, and Tb2+, which have ground-state or low-lying d1 electronic configurations. Lu2+, with an accessible d1 electronic configuration but a rather high electron affinity, reacted only through transfer channels. The remaining Ln2+ reacted via transfer channels or adduct formation. The different accessibilities of d1 electronic configurations and the range of electron affinities of the Ln2+ cations allowed for a detailed analysis of the trends for metal(2+) reactivity and the conditions for occurrence of bond activation, adduct formation, and electron, hydride, and methide transfers

Gas-phase energies of actinide oxides -- an assessment of neutral and cationic monoxides and dioxides from thorium to curium

An assessment of the gas-phase energetics of neutral and singly and doubly charged cationic actinide monoxides and dioxides of thorium, protactinium, uranium, neptunium, plutonium, americium, and curium is presented. A consistent set of metal-oxygen bond dissociation enthalpies, ionization energies, and enthalpies of formation, including new or revised values, is proposed, mainly based on recent experimental data and on correlations with the electronic energetics of the atoms or cations and with condensed-phase thermochemistry

MOLECULAR SPECTROSCPY AND REACTIONS OF ACTINIDES IN THE GAS PHASE AND CRYOGENIC MATRICES

In this chapter we review the spectroscopic data for actinide molecules and the reaction dynamics for atomic and molecular actinides that have been examined in the gas phase or in inert cryogenic matrices. The motivation for this type of investigation is that physical properties and reactions can be studied in the absence of external perturbations (gas phase) or under minimally perturbing conditions (cryogenic matrices). This information can be compared directly with the results from high-level theoretical models. The interplay between experiment and theory is critically important for advancing our understanding of actinide chemistry. For example, elucidation of the role of the 5f electrons in bonding and reactivity can only be achieved through the application of experimentally verified theoretical models. Theoretical calculations for the actinides are challenging due the large numbers of electrons that must be treated explicitly and the presence of strong relativistic effects. This topic has been reviewed in depth in Chapter 17 of this series. One of the goals of the experimental work described in this chapter has been to provide benchmark data that can be used to evaluate both empirical and ab initio theoretical models. While gas-phase data are the most suitable for comparison with theoretical calculations, there are technical difficulties entailed in generating workable densities of gas-phase actinide molecules that have limited the range of species that have been characterized. Many of the compounds of interest are refractory, and problems associated with the use of high temperature vapors have complicated measurements of spectra, ionization energies, and reactions. One approach that has proved to be especially valuable in overcoming this difficulty has been the use of pulsed laser ablation to generate plumes of vapor from refractory actinide-containing materials. The vapor is entrained in an inert gas, which can be used to cool the actinide species to room temperature or below. For many spectroscopic measurements, low temperatures have been achieved by co-condensing the actinide vapor in rare gas or inert molecule host matrices. Spectra recorded in matrices are usually considered to be minimally perturbed. Trapping the products from gas-phase reactions that occur when trace quantities of reactants are added to the inert host gas has resulted in the discovery of many new actinide species. Selected aspects of the matrix isolation data were discussed in chapter 17. In the present chapter we review the spectroscopic matrix data in terms of its relationship to gas-phase measurements, and update the description of the new reaction products found in matrices to reflect the developments that have occurred during the past two years. Spectra recorded in matrix environments are usually considered to be minimally perturbed, and this expectation is borne out for many closed shell actinide molecules. However, there is growing evidence that significant perturbations can occur for open shell molecules, resulting in geometric distortions and/or electronic state reordering. Studies of actinide reactions in the gas phase provide an opportunity to probe the relationship between electronic structure and reactivity. Much of this work has focused on the reactions of ionic species, as these may be selected and controlled using various forms of mass spectrometry. As an example of the type of insight derived from reaction studies, it has been established that the reaction barriers for An+ ions are determined by the promotion energies required to achieve the 5fn6d7s configuration. Gas-phase reaction studies also provide fundamental thermodynamic properties such as bond dissociation and ionization energies. In recent years, an increased number of gas-phase ion chemistry studies of bare (atomic) and ligated (molecular) actinide ions have appeared, in which relevant contributions to fundamental actinide chemistry have been made. These studies were initiated in the 1970's and carried out in an uninterrupted way over the course of the past three decades. Initial studies unsurprisingly focused on naturally occurring U (and Th) and were later extended (starting ten years ago) to Pa and several of the more abundant members of the transuranium series, Np through Es. The main purpose of the reaction dynamics section of this chapter is to summarize (up to late 2008) the work done in the gas phase involving ionic species, with an emphasis on the key accomplishments. This topic was recently reviewed in a comprehensive way (Gibson 2002a; Gibson and Marcalo 2006). The small number of studies reported for gas-phase reactions of neutral actinide species are also briefly summarized

Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States

Pentavalent actinyl nitrate complexes AnVO2(NO3)2- were produced by elimination of two NO2 from AnIII(NO3)4- for An = Pu, Am, Cm, Bk and Cf. Density functional theory (B3LYP) and relativistic multireference (CASPT2) calculations confirmed the AnO2(NO3)2- as AnVO2+ actinyl moieties coordinated by nitrates. Computations of alternative AnIIIO2(NO3)2- and AnIVO2(NO3)2- revealed significantly higher energies. Previous computations for bare AnO2+ indicated AnVO2+ for An = Pu, Am, Cf and Bk, but CmIIIO2+: electron donation from nitrate ligands has here stabilized the first CmV complex, CmVO2(NO3)2-. Structural parameters and bonding analyses indicate increasing An-NO3 bond covalency from Pu to Cf, in accord with principles for actinide separations. Atomic ionization energies effectively predict relative stabilities of oxidation states; more reliable energies are needed for the actinides.JRC.G.I.5-Advanced Nuclear Knowledg

Molecular uranates - laser synthesis of uranium oxide anions in the gas phase

Laser ablation of solid UO{sub 3} or (NH{sub 4}){sub 2}U{sub 2}O{sub 7} yielded in the gas phase molecular uranium oxide anions with compositions ranging from [UO{sub n}]{sup -} (n = 2-4) to [U{sub 14}O{sub n}]{sup -} (n = 32-35), as detected by Fourier transform ion cyclotron resonance mass spectrometry. The cluster series [U{sub x}O{sub 3x}]{sup -} for x {le} 6 and various [U{sub x}O{sub 3x-y}]{sup -}, in which y increased with increasing x, could be identified. A few anions with H atoms were also present, and their abundance increased when hydrated UO{sub 3} was used in place of anhydrous UO{sub 3}. Collision-induced dissociation experiments with some of the lower m/z cluster anions supported extended structures in which neutral UO{sub 3} constitutes the building block. Cationic uranium oxide clusters [U{sub x}O{sub n}]{sup +} (x = 2-9; n = 3-24) could also be produced and are briefly discussed. Common trends in the O/U ratios for both negative and positive clusters could be unveiled

Gas-Phase Oxidation of Cm+ and Cm2+ -- Thermodynamics of neutral and ionized CmO

Fourier transform ion cyclotron resonance mass spectrometry was employed to study the products and kinetics of gas-phase reactions of Cm+ and Cm2+; parallel studies were carried out with La+/2+, Gd+/2+ and Lu+/2+. Reactions with oxygen-donor molecules provided estimates for the bond dissociation energies, D[M+-O](M = Cm, Gd, Lu). The first ionization energy, IE[CmO], was obtained from the reactivity of CmO+ with dienes, and the second ionization energies, IE[MO+](M = Cm, La, Gd, Lu), from the rates of electron-transfer reactions from neutrals to the MO2+ ions. The following thermodynamic quantities for curium oxide molecules were obtained: IE[CmO]= 6.4+-0.2 eV; IE[CmO+]= 15.8+-0.4 eV; D[Cm-O]= 710+-45 kJ mol-1; D[Cm+-O]= 670+-40 kJ mol-1; and D[Cm2+-O]= 342+-55 kJ mol-1. Estimates for the M2+-O bond energies for M = Cm, La, Gd and Lu are all intermediate between D[N2-O]and D[OC-O]--i.e., 167 kJ mol-1&lt; D[M2+-O]&lt; 532 kJ mol-1 -- such that the four MO2+ ions fulfill the thermodynamic requirement for catalytic O-atom transport from N2O to CO. It was demonstrated that the kinetics are also favorable and that the CmO2+, LaO2+, GdO2+ and LuO2+ dipositive ions each catalyze the gas-phase oxidation of CO to CO2 by N2O. The CmO2+ ion appeared during the reaction of Cm+ with O2 when the intermediate, CmO+, was not collisionally cooled -- although its formation is kinetically and/or thermodynamically unfavorable, CmO2+ is a stable species