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Gas-Phase Ion Chemistry (gas-phase + ion_chemistry)
Selected AbstractsSpecific Processes and Scrambling in the Dehydrogenation of Ethane and the Degenerate Hydrogen Exchange in the Gas-Phase Ion Chemistry of the Ni(C,H3,O)+/C2H6 CoupleHELVETICA CHIMICA ACTA, Issue 5 2007Maria Schlangen Abstract A mechanistically unprecedented situation characterizes the gas-phase ion chemistry of Ni(C,H3,O)+ when reacted under thermal, single-collision conditions with ethane. A dehydrogenation channel leading to Ni(C3,H7,O)+ is to 90% preceded by a complete loss of positional identity of all nine H-atoms of the encounter complex (,scrambling'), whereas ca. 10% of the reaction exhibit a selective CH bond activation of the alkane. In addition, a degenerate H exchange between ethane and the (C,H3,O) unit occurs as a side reaction, the mechanistic details of which remain unknown for the time being. [source] Gas-Phase Ion Chemistry of BF3/NH3 Mixtures.CHEMINFORM, Issue 6 2007Federico Pepi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Gas-Phase Ion Chemistry of BF3/HN3 Mixtures: The First Observation of [BFnNxHn-1]+ (n = 1, 2; x = 1, 3) Ions.CHEMINFORM, Issue 28 2006Federico Pepi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Gas-phase ion chemistry in the ternary silane,propyne,phosphine systemJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2004Lorenza Operti Abstract The gas-phase ion chemistry of propyne,phosphine and silane,propyne,phosphine mixtures was studied by ion trap mass spectrometry. For the binary mixture, the effect of different partial pressures of the reagents on the yield of C and P-containing ions was evaluated. Reaction sequences and rate constants were determined and reaction efficiencies were calculated from comparison of experimental and collisional rate constants. In the ternary silane,propyne,phosphine systems, the reaction pathways leading to formation of SimCnPpHq+ ions were determined and the rate constants of the most important steps were measured. For some ion species, selected by double isolation procedures (MS/MS), the low ion abundances prevented determination of the reaction rate constants. Si, C and P-containing ions are mainly produced in reactions of SimPpHq+ ions with propyne, while the reactivity of the SimCnHq+ ions towards PH3 and of the CnPpHq+ ions towards SiH4 is very low. The formation of hydrogenated SiCP ions is interesting for their possible role as precursors of amorphous silicon carbides doped with phosphorus, obtained in a single step, by deposition from properly activated silane,propyne,phosphine mixtures. Copyright © 2004 John Wiley & Sons, Ltd. [source] Gas-phase ion chemistry in the ternary SiH4,C3H6,PH3 systemJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2002Stefania Calderan Abstract Propene,phosphine and the silane,propene,phosphine gaseous mixtures were studied by ion trap mass spectrometry. For the binary mixture the variation of ion abundances under different partial pressures and the mechanisms of ion,molecule reactions are reported. Moreover, the rate constants of the main processes were measured and compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane,propene,phosphine mixture the mechanisms of formation of ion clusters were elucidated, but the complexity of the system and the low abundances of the ions usually isolated by successive steps prevented the determination of rate constants. The hydrogenated ternary ions are mainly formed by reactions of ions with propene, whereas a minor contribution comes from reactions of ions with phosphine. The ions show very low reactivity with silane. The formation processes of these species are discussed in relation to their possible role as precursors of amorphous silicon carbides doped with phosphorus obtained by deposition from properly activated silane,propene,phosphine mixtures. Copyright © 2001 John Wiley & Sons, Ltd. [source] Gas-phase ion chemistry of Glu/Met systems,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 1 2002H. Wincel A combined chemical ionisation and tandem mass spectrometry (MS/MS) approach has been used for investigation of the gas-phase ion chemistry of systems containing the amino acids Glu and Met, and the dipeptides ,-Glu-Met and Met-Glu. The metastable fragmentation of the protonated dimer, (Glu)2H+, reveals an intracluster reaction leading to the elimination of the Glu residue. The main features of the ion-molecule reactions observed in the systems containing Glu and Glu,+,Met can be described in terms of sequential adduct formation. The results obtained for the thermal dehydration of Glu were used to rationalise the formation of the proton-bound structures (Glu,,,H2O)···H+··· (Glu,,,H2O) and (Glu,,,H2O)3·H+. The adduct ions, [(Glu,,,H2O),+,H,+,Glu]+ and [(Glu,,,H2O),+ H,+,Met]+, and further association products were also observed. The results lead to a reconsideration of the structural aspects proposed earlier for these species in the sense that they suggest that the systems correspond to a mixture of isomeric covalent and proton-bound structures. The thermal effects on the decomposition of the neutral (,-Glu-Met) and its protonated form, (,-Glu-Met)H+, at m/z 279 were investigated, and dramatic changes in the MI spectra of the m/z 279 ion with temperature were found. A mechanistic explanation for the observed evolution of higher mass ion peaks in the mass spectra is developed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Specific Processes and Scrambling in the Dehydrogenation of Ethane and the Degenerate Hydrogen Exchange in the Gas-Phase Ion Chemistry of the Ni(C,H3,O)+/C2H6 CoupleHELVETICA CHIMICA ACTA, Issue 5 2007Maria Schlangen Abstract A mechanistically unprecedented situation characterizes the gas-phase ion chemistry of Ni(C,H3,O)+ when reacted under thermal, single-collision conditions with ethane. A dehydrogenation channel leading to Ni(C3,H7,O)+ is to 90% preceded by a complete loss of positional identity of all nine H-atoms of the encounter complex (,scrambling'), whereas ca. 10% of the reaction exhibit a selective CH bond activation of the alkane. In addition, a degenerate H exchange between ethane and the (C,H3,O) unit occurs as a side reaction, the mechanistic details of which remain unknown for the time being. [source] Gas phase behavior of radical cations of perfluoroalkyl-1,2,4-triazines: an experimental and theoretical studyJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2009Gianluca Giorgi Abstract Electron ionization mass spectrometry and low-energy collision-induced decomposition reactions occurring in a tridimensional ion trap, together with density functional theory (DFT) calculations on neutrals, even- and odd-electron cations, have been used to study the gas-phase ion chemistry of a series of perfluoroalkyl-1,2,4-triazines. Loss of oxygen, due to thermal degradation occurring before ionization, likely involving the hydroxylamino group, has been observed. Compounds having a carbonyl group at position 6 of the triazine ring fragment in the source by elimination of NO followed by HF or CO. The decomposition pathways occurring due to CID experiments have shown interesting features depending on the nature and structure of precursor ions. Most of them involve elimination of endocyclic atoms, thereby producing contraction of the original six-membered ring or formation of acyclic structures. DFT (B3LYP/6-31G(d,p)) calculations have been used for evaluating structure, stability and properties of neutral and ionic species involved in gas-phase processes. In particular, it has been calculated that in the molecular ion the unpaired electron is mainly located on the exocyclic nitrogen, while the positive charge is on the C(6) carbon atom. Copyright © 2009 John Wiley & Sons, Ltd. [source] Gas-phase ion chemistry of Glu/Met systems,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 1 2002H. Wincel A combined chemical ionisation and tandem mass spectrometry (MS/MS) approach has been used for investigation of the gas-phase ion chemistry of systems containing the amino acids Glu and Met, and the dipeptides ,-Glu-Met and Met-Glu. The metastable fragmentation of the protonated dimer, (Glu)2H+, reveals an intracluster reaction leading to the elimination of the Glu residue. The main features of the ion-molecule reactions observed in the systems containing Glu and Glu,+,Met can be described in terms of sequential adduct formation. The results obtained for the thermal dehydration of Glu were used to rationalise the formation of the proton-bound structures (Glu,,,H2O)···H+··· (Glu,,,H2O) and (Glu,,,H2O)3·H+. The adduct ions, [(Glu,,,H2O),+,H,+,Glu]+ and [(Glu,,,H2O),+ H,+,Met]+, and further association products were also observed. The results lead to a reconsideration of the structural aspects proposed earlier for these species in the sense that they suggest that the systems correspond to a mixture of isomeric covalent and proton-bound structures. The thermal effects on the decomposition of the neutral (,-Glu-Met) and its protonated form, (,-Glu-Met)H+, at m/z 279 were investigated, and dramatic changes in the MI spectra of the m/z 279 ion with temperature were found. A mechanistic explanation for the observed evolution of higher mass ion peaks in the mass spectra is developed. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||