Zeev Karpas - Academia.edu (original) (raw)

Papers by Zeev Karpas

CRC Press eBooks, Nov 21, 2014

Division of Waste Management and Radiation Control Utah Chemistry Help | Chegg.comUranium Wikiped... more Division of Waste Management and Radiation Control Utah Chemistry Help | Chegg.comUranium WikipediaNuclear Energy Basics: How Is Power Produced?Home ACZ LaboratoriesSolvent Extraction an overview | ScienceDirect TopicsUranium | U (Element) PubChemUranium 235 an overview | ScienceDirect TopicsEnvironmental Science & Technology Letters | 标准期刊缩写 ...Energy and Environmental Sciences | 标准期刊缩写 (ISO4 (PDF) Fundamentals of Analytical Chemistry9th Edition Search NY Labs Current scope as ofFreshwater environmental quality parameters WikipediaWhat is a Geologic Map?Analytical Chemistry(PDF) Environmental Chemistry-Manahan (7th Edition)-Ebook Uranium | U PubChemAnalytical Chemistry MSc degree course London Environmental Analytical Laboratories | Saskatchewan Hyperstoichiometric Uranium Dioxides: Rapid Synthesis and List of Chemistry Articles BYJU'S Chemistry Articles LibraryNortheast Laboratory Services: Answers for a Healthier PCCL Physics and Chemistry by a Clear LearningChemistry Introduction, Branches, Concepts, Free Resources

PubMed, Dec 1, 1989

The potential of ion mobility spectrometry (IMS) as a sensitive method for detecting hidden explo... more The potential of ion mobility spectrometry (IMS) as a sensitive method for detecting hidden explosives and contraband drugs has been recognized since the advent of the technique twenty years ago. The IMS performed extremely well in laboratory studies of single-component chemical systems, and detection limits of sub-part-per-billion were reported for explosive vapor. However, in order to overcome the problems encountered in monitoring vapors in the ambient atmosphere, special means were needed to increase the sensitivity and specificity of IMS instruments. It took over a decade until single purpose IMS instruments were developed. These portable (or even hand-held) instruments are presently being tested as monitors for detection and identification of drugs or explosives, with sensitivity and specify that are unrivaled by other techniques.

CRC Press eBooks, Nov 26, 2013

The Journal of Physical Chemistry, Oct 1, 1989

The effects of temperature and clustering on the mobility of ions drifting in C 0 2 at ambient pr... more The effects of temperature and clustering on the mobility of ions drifting in C 0 2 at ambient pressure were studied by ion mobility spectrometry (IMS). A semiempirical procedure for obtaining quantitative data on the size of the cluster was applied. At 90 O C , about three C02 molecules, on average, clustered around protonated amine core ions. As the temperature was raised, the number of clustered molecules decreased, and above 200 O C , it was practically zero. A clear mass-mobility correlation was observed in the protonated aliphatic amines even at 90 O C. Protonated pyridine, picoline, lutidine, and collidine were unresolved at this temperature, but as the temperature was raised, resolution improved. On the whole, use of COz as a drift gas in IMS, although inferior in some cases, should not be precluded.

International Journal of Mass Spectrometry and Ion Processes, Dec 1, 1986

ABSTRACT

Structural Chemistry, 1990

ABSTRACT Ion mobility spectrometry (IMS) and IMS/MS techniques were used to differentiate between... more ABSTRACT Ion mobility spectrometry (IMS) and IMS/MS techniques were used to differentiate between nitrogenprotonated and carbon-protonated anilines, both of which coexist under the conditions of the IMS. Analysis of the results led to the conclusion that the former species had lower mobilities than the latter. This was attributed mainly to charge delocalization in the ring-protonated species, which results in a weaker interaction with the drift gas molecules. Furthermore,meta-alkyl substitution enhanced ring protonation, while in 2-chloroaniline the nitrogenprotonated species was predominant, as expected.

Journal of the American Society for Mass Spectrometry, Mar 1, 1994

Chemischer Informationsdienst, Dec 26, 1978

International Journal of Mass Spectrometry and Ion Physics, Mar 1, 1975

Abstract The ion—molecule reactions taking place in gaseous monomeric formaldehyde under electron... more Abstract The ion—molecule reactions taking place in gaseous monomeric formaldehyde under electron impact have been studied by ion cyclotron resonance techniques. The main reaction product at low pressures is the secondary ion CH 3 O + , which is formed by proton transfer from either of the two primary ions, CH 2 O + or CHO + , to the neutral formaldehyde molecule. At higher pressures a number of proton transfer and hydrogen abstraction reactions are observed involving additional fragment ions producing secondary and tertiary ions, such as CH 4 O + CH 5 O + , CH 2 + and CH 3 + . At still higher pressures, product ions containing two carbon atoms are formed by complex reactions. The identity of all ions was verified by use of deuterium and 18 O-labelled formaldehyde. Double resonance techniques were applied to confirm the reaction channel and to determine some of the reaction mechanisms. Relative rate constants of the main reactions were measured.

International Journal of Mass Spectrometry and Ion Processes, Apr 1, 1994

Cluster size distribution and collision-induced dissociation (CID) studies of protonated methanol... more Cluster size distribution and collision-induced dissociation (CID) studies of protonated methanol and protonated methanol-water clusters yield information on the structure and energetics of such ions. Ions were formed at atmospheric pressure in a corona discharge source, and were subjected to CID in the center quadrupole of a triple quadrupole mass spectrometer. Cluster ions containing up to 13 molecules of methanol and/or water were observed and examined using CID experiments. The CID of all (CH,OH),-H,O * H + clusters, where n ,< 8, showed that water loss was statistically favored over methanol loss and that the preferred dissociation channel involved loss of water with methanol molecules. These results support a model employing a chain of hydrogen-bonded solvent molecules rather than one in which fused rings of ligands surround a central hydronium ion. However, CID of larger clusters, where n 2 9, showed that loss of one methanol was equal to or less than loss of water, reflecting a change in structure.

Chemischer Informationsdienst, Feb 4, 1986

ChemInform Abstract Die anhand von Protonierungsreaktionen in der Gasphase zugänglichen Bildungsw... more ChemInform Abstract Die anhand von Protonierungsreaktionen in der Gasphase zugänglichen Bildungswärmen der Singulett-Carbene CFZ, CFCl, CHF, CCl2, CHCl steigen in der angegebenen Reihenfolge von-49 auf + 71 kcal/mol an (Protonenaffinität, C-H-und C-X-Bindungsstärken).

Chemischer Informationsdienst, Mar 18, 1986

ChemInform Abstract Als einzige Reaktion der Ausgangsionen HF(+) und HF wird Reaktion A beobachte... more ChemInform Abstract Als einzige Reaktion der Ausgangsionen HF(+) und HF wird Reaktion A beobachtet, deren bimolekulare Geschwindigkeitskonstante bestimmt wird. Zur Ermittlung der Protonenaffinität von HF werden Protonenübertragungsreaktionen in Mischungen von HF mit N2, CH4 und CO2 untersucht. Aus der gemessenen Gleichgewichtskonstanten und bestimmten Entropieänderung wird ein Wert für AH der Reaktion B berechnet.

Chemischer Informationsdienst, Nov 18, 1986

ChemInform Abstract The reaction ROH2+ + HCN → RNCH+ + H2O is observed in mixtures containing alc... more ChemInform Abstract The reaction ROH2+ + HCN → RNCH+ + H2O is observed in mixtures containing alcohols and HCN. Proton affinity bracketing experiments show that the products are protonated isocyanides, RNCH+, which are formed by alkylation of the nitrogen in HCN, rather than protonated Cyanides, RCNH+. Although the latter are more stable, their production would require rearrangement. Similar reactions are observed between (CH3)2OH+ and RSH2+ and HCN. CH3CN and HC3N (cyanoacetylene) can also be alkylated in similar fashion to form the nitrilium ions CH3CNCH3+ and HC3NCH3+, respectively. In cases where the proton affinity of the nitrile is higher than that of the alcohol, alkylation occurs by a condensation reaction, such as in methanol and acetonitrile: CH3CNH+ + CH3OH → CH3NCCH3+ + H2O. The rate constants for the alkylation reactions are generally in the range of (1-10)•10-11 cm3 s-1 and are not affected significantly by the reaction exothermicity or by the structure of the reactants. These reactions may contribute to the synthesis of isocyanides in interstellar clouds and planetary atmospheres.