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1

Nitrogen-15 Kinetic Isotope Effects in the Decomposition of Nitric Oxide on Copper

100%

Polič S. , Senegačnik M. , Kobal I. , Zieliński M.

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2002

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tom Vol. 76 / nr 7

1009-1018

EN

Isotopic rate constant ratios, k14/k15, have been determined for the decomposition of nitric oxide over copper wire at initial NO pressures 40-60 kPa over temperature range 725-825 K. They were interpreted using the Bigeleisen formalism. Under these experimental conditions the reaction was found to be second order in NO. On the basis of the temperature independence, k14/k15 = 1.010 š 0.001 at all temperatures studied, a cis ONNO transition state was shown to account satisfactorily for the experimental k14/k15 values.

2

Activated Complex in the Decomposition of N2O over Cu

100%

Polie S. , Senegaenik M. , Kobal I. , Zieliński M.

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2001

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tom Vol. 75, nr 11

1729-1729

EN

Decomposition of N2O over Cu wire, at initial N2O pressures 40–60 kPa and temperatures 675–875 K, showed first order kinetics inN2Owith an apparent activation energy of 110 š 16 kJ mol–1. The 15N and 18O kinetic isotope effects under these experimental conditions were determined and interpreted following the Bigeleisen’s formalism. A bent NNO activated complex satisfactorily accounts for the experimental results.

3

Background outdoor radon levels in Slovenia

100%

Vaupotič J. , Kobal I. , Križman M. J.

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tom Vol. 55, No. 4

579-582

EN

Radon (222Rn) activity concentration in outdoor air was measured by exposing track etch detectors at 60 points. Values were found in the range of 3.7–41.0 Bqźm–3, with a geometric mean (GM) of 11.8 Bqźm–3 and geometric standard deviation (GSD) of 2.2. An outdoor radon map of Slovenia was drawn, showing the majority of elevated values to be in the south-west part of the country that is covered by carbonates.

4

Carbon-13 isotope effect for decarboxylation of phenylpropiolic acid (PPA) in concentrated phosphoric acids

88%

Zieliński M. , Zielińska A. , Papiernik-Zielińska H. , Ogrinc N. , Kobal I.

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2000

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tom Vol. 45, nr 2

121-124

EN

13C isotope effects on the decarboxylation of phenylpropiolic acid (PPA) in 93–97% H3PO4 and in 23% diphosphoric acid in orthophosphoric acid have been investigated from 293 to 353 K. The initial 13C fractionations in all three systems are in agreement with the 13C decarboxylation fractionations expected assuming the loss of the one carbon-carbon bond in the transition state. In 100% H3PO4 and in 23% diphosphoric acid in orthophosphoric acid later fractions of carbon dioxide are depleted in carbon-13 to a greater degree than expected, probably due to isotopic preequilibria between stable and decarboxylating forms of PPA. At 353 K and higher temperature strong deviations of the experimental rate constants and of the experimental 13C fractionations from the values extrapolated from lower temperature are observed. A tentative decarboxylation scheme operating in concentrated phosphoric acid media is proposed.

5

Carbon-13 Kinetic Isotope Effect for the Decarbonylation of Liquid Formic Acid Assisted with Uranium Trioxide, Uranium Peroxide and Uranyl Formate

88%

Zieliński M. , Zielińska A. , Ogrinc M. , Papiernik-Zielińska H. , Kobal I.

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2000

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tom Vol. 74, nr 10

1427-1427

EN

13C KIE’s in the decarbonylation of liquid formic acid (FA) in the presence of uranium trioxide, UO3, uranium peroxide, UO4, and in the presence of uranyl formate, UO2(HCOO)2, produced in the reaction of the above two uranium oxides with FA have been investigated between 90–120°C. Decarbonylation of HCOOH assisted with uranium trioxide proceeds with normal 13C KIE, expected assuming that 13C–16O bond is broken in the transition state, (k12/k13) KIE = 1.0496/at 100°C. The decarbonylation of liquid formic acid in the presence of uranium peroxide and uranyl formate is accompanied with 13C KIE of intermediate value, which is higher than the 13C KIE observed in the decarbonylation of pure FA, but smaller than the maximum 13C KIE expected for complete rupture of the single carbon–oxygen bond in the decarbonylation T.S. of the protonated formic acid. A mechanism of decomposition of formic acid in the presence of uranium oxides is proposed.

6

Introduction to Studies of Deuterium Isotope Effects on the Decarboxylation 13C KIE and on the Decarboxylation of the Phenylpropiolic Acid (PPA) in D3PO4/D2O Solution

88%

Zieliński M. , Zielińska A. , Ogrinc N. , Kobal I. , Papiernik-Zielińska H.

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2000

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tom Vol. 74, nr 12

1743-1749

EN

Carbon-13 kinetic isotope effect (KIE) in the decarboxylation of phenylpropiolic acid (PPA) in 85% D3PO4 in D2O has been studied and compared with the 13C KIE in decarboxylation of PPA in 85% H3PO4 in H2O. The decarboxylation of PPA in 85% D3PO4 in D2O solution proceeds with slower rate than in 85% H3PO4 solution in H2O in agreement with the proposed mechanism of decarboxylation, which involves the protonation of the triple bond of PPA in the rate determining step. The very negligible decarboxylation 13C KIE equal: (k12/k13)D = 1.0006 0.0012 in 85% D3PO4/D2O medium in the 70–90 graduate C interval, corroborates strongly the previous conclusions drawn from (k12/k13) values found in 85% H3PO4 water solutions. Formation of the sp2(C-D) bond in the decarboxylation transition state inD3PO4/D2Osolutions takes place with less steric requirements than the sp2(C–H) bond formation in H3PO4/H2O medium.

7

Carbon-13 Isotope Effect for Carbon Dioxide Formation in the Reaction of Liquid Formic Acid with Uranium Trioxide

88%

Zieliński M. , Zielińska A. , Ogrinc N. , Papiernik-Zielińska H. , Kobal I.

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2001

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tom Vol. 75, nr 6

889-894

8

Identification of radon anomalies in soil gas using decision trees and neural networks

88%

Zmazek B. , Džeroski S. , Torkar D. , Vaupotič J. , Kobal I.

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tom Vol. 55, No. 4

501-505

EN

The time series of radon (222Rn) concentration in soil gas at a fault, together with the environmental parameters, have been analysed applying two machine learning techniques: (i) decision trees and (ii) neural networks, with the aim at identifying radon anomalies caused by seismic events and not simply ascribed to the effect of the environmental parameters. By applying neural networks, 10 radon anomalies were observed for 12 earthquakes, while with decision trees, the anomaly was found for every earthquake, but, undesirably, some anomalies appeared also during periods without earthquakes.

9

A radon anomaly in soil gas at Cazzaso,NE Italy, as a precursor of an ML = 5.1 earthquake

88%

Vaupotič J. , Riggio A. , Santulin M. , Zmazek B. , Kobal I.

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tom Vol. 55, No. 4

507-511

EN

At Cazzaso (Friuli) in northeast Italy, radon (222Rn) activity concentration in soil gas in a borehole at a depth of 80 cm has been monitored continuously (at a frequency of once an hour) since May 2004, using a Barasol probe (Algade, France). In addition, environmental parameters (air and soil temperature, barometric pressure) have been recorded. The results have been evaluated and the relationship between radon levels and seismic activity is discussed. Correlation between radon concentration and barometric pressure has been observed. Preliminary results have shown a distinct radon anomaly prior to some earthquakes.

10

Carbon-13 fractionation in the oxidation of propionate of natural isotopic composition with permanganate and manganate

75%

Zieliński M. , Fry A. , Zielińska A. , Ogrinc N. , Papiernik-Zielińska H. , Kobal I.

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2000

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tom Vol. 45, nr 4

221-224

EN

Carbon-13 fractionation in the oxidation of sodium propionate of natural isotopic composition with permanganate in water solution and with manganate in alkaline solution has been investigated and compared with carbon-14 kinetic isotope effects in the oxidation of (3-14C) – and (2-14C) propionate with permanganate. The experimental carbon-13 isotope ratios, R(13C/12C)cumul., corrected for dilution of R(13C/12C)a by carbon dioxide derived from all external sources and by carbon dioxide derived from (C-1) and from (C-3) of propionate at its complete and partial oxidations, used for calculation of 13C alfa KIE, provided the carbon-13 isotope effects corresponding to initial oxidation of alpha carbon, which correlate well with (2-14C) KIE determined previously, (k12/k13 -1)?100 ? 1/2(k12/k14 -1)?100 ? 1/2(4.6š0.3) at 373 K. The possibility of extension of isotope ratio measurements, using modern double collector mass spectrometers, from geochemical, biomedical, agriculture and environmental research to carbon-13 isotope effects studies in chemical organic reactions is briefly discussed.