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  • Analytical Chemistry and Spectroscopy  (27)
  • Stabilities and reactivities  (1)
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  • 11
    Digitale Medien
    Digitale Medien
    Polarizabilites of organic ions (1986)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 21 (1986), S. 449-450 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210210717
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  • 12
    Digitale Medien
    Digitale Medien
    Doubly-charged ethane ions: Solution to the dilemma of stability predicted by theory and instability observed in experiment (1986)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 21 (1986), S. 479-483 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Potential energy curves have been computed for [C2H6]2+ ions and the results used to interpret the conspicuous absence of these ions in 2E mass spectra and in charge-stripping experiments. The energies and structures of geometry-optimized ground-state singlet and excited-state triplet [C2H6]2+ ions have been determined along with energies for different decomposition barriers and dissociation asymptotes. Although singlet and triplet [C2H6]2+ ions can exist as stable entities, they possess low energy barriers to decomposition. Vertical Franck-Condon transitions, involving electron impact ionization of ethane as well as charge-stripping collisions of [C2H6]+ ions, produce [C2H6]2+ ions which promptly dissociate since they are formed with energies in excess of various decomposition barriers. Appearance energies computed for doubly-charged ethane fragment ions are in accordance with experimental values.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210210806
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  • 13
    Digitale Medien
    Digitale Medien
    Charge neutralization of ions from benzene (1988)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 23 (1988), S. 256-260 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Cross-sections have been measured for the charge neutrilization if ions from benzene in kiloelectron-volt collisions with benezene target molecules. Measured values range from 65 Å2 for the symmetric [C6H6]+—C6H6 resonant reactions to 8 Å2 for [C3H3]+—C6H6 reactions. Cross-sections computed using a simple resonance charge transfer model compare favourably with experimental data for the symmetric reactions. The cross-sections for asymmetric reactions are smaller that those for they symmetric system and magnitudes of the asymmetric cross-sections are correlated with recombination energies of the respective ions.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210230407
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  • 14
    Digitale Medien
    Digitale Medien
    Doubly charged ion mass spectra of alkyl-substituted furans and pyrroles (1987)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 22 (1987), S. 389-399 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Doubly charged ion mass spectra of alkyl-substituted furans and pyrroles were obtained using a double-focusing magnetic mass spectrometer operated at 3.2 kV accelerating voltage. Molecular ions were the dominant species found in doubly charged spectra of lower molecular weight heterocydic compounds, whereas the spectra of the higher weight homologues were typified by abundant fragment ions from extensive decomposition. Measured doubly charged ionization and appearance energies ranged from 22.8 to 47.9 eV. Ionization energies were correlated with values calculated using self-consistent field-molecular orbital techniques. A multichannel diabatic curve-crossing model was developed to investigate the fundamental organic ion reactions responsible for development of doubly charged ion mass spectra. Probabilities for Landau-Zener type transitions between reactant and product curves were determined and used in the collision model to predict charge-transfer cross-sections, which compared favorably with experimental cross-sections obtained using time-of-flight techniques.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210220703
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  • 15
    Digitale Medien
    Digitale Medien
    Doubly charged ion mass spectra. 2 - aromatic hydrocarbons (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 92-98 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Doubly charged ion mass spectra for 15 aromatic hydrocarbons have been obtained using a Nier-Johnson geometry, Hitachi RMU-7L mass spectrometer operating at 1.6 kV accelerating voltage. The doubly charged ion spectra have features that are characteristic of the individual compounds. Unsaturated aromatic molecules show intense molecular ions in contrast to saturated, substituted or heteroatom compounds which undergo extensive fragmentation. Ionization energies for forming doubly charged molecular ions and appearance energies for the prominent doubly charged fragment ions have been measured. Calculations of the SCF energies and structures of various doubly charged ions have been carried out. Measured and calculated ionization/appearance energies are in reasonable accord and lend support to the suggested ion structures.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210160210
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  • 16
    Digitale Medien
    Digitale Medien
    Doubly charged ion mass spectra 8 - alkenes (1984)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1984), S. 412-422 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Doubly charged ion mass spectra of 23 alkenes have been measured using a double focusing Hitachi RMU-7L mass spectrometer. Ion mass spectra were obtained using 100 eV electron energy and 3.2 kV ion accelerating voltage. Each 2E spectrum was determined using the olefinic compound under investigation as the target gas. In general, spectra are dominated by fragment ions which result from extensive hydrogen loss from the doubly charged molecular ion. Appearnce energies have been measured for intense fragment ions in each spectrum.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210190903
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  • 17
    Digitale Medien
    Digitale Medien
    Doubly charged ion mass spectra: III - N-alkanes (1982)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 17 (1982), S. 10-18 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Doubly charged ion mass spectra have been obtained for 15 n-alkane hydrocarbons. Spectra were measured using a Nier-Johnson geometry Hitachi RMU-7L mass spectrometer operated at 1.6kV accelerating voltage. Fragment ions, which resulted from C—C bond rupture and extensive H loss, dominated the spectra. Molecular ions have not been observed. The most intense ions in the doubly charged ion mass spectra of n-alkanes were [C2H4]2+, [C3H2]2+, [C4H3]2+, [C5H2]2+, [C6H6]2+, [C6H8]2+, [C7H6]2+, [C7H8]2+, [C8H6]2+ and [C8H8]2+. Appearance energies for forming the prominent doubly charged fragment ions have been measured and range from 27.5 eV to energies greater than 60eV. A geometry optimized SCF approach has been used to compute the energies and structures of prominent ions in the doubly charged mass spectra.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210170103
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  • 18
    Digitale Medien
    Digitale Medien
    Doubly charged ion mass spectra. 7 - acetylenes (1983)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 18 (1983), S. 282-294 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Doubly charged ion mass spectra of 20 aliphatic and 3 aromatic acetylenic compounds have been measured using a double focusing Hitachi RMU-7L mass spectrometer. Spectra were obtained using 100 eV ionizing electron energy and 3.2 kV ion accelerating voltage. In general, the spectra of aliphatic type acetylenic compounds were dominated by fragment ions formed by extensive H loss from doubly charged molecular ions. Intense molecular ions were observed in the doubly charged ion spectra of phenyl-substituted acetylenes. Total product ion intensities for doubly charged ion spectra of acetylenic compounds were found to be smaller, in general, than the total product ion intensity observed in the benzene doubly charged ion mass spectrum. Measured appearance energies of intense product ions ranged from 24 to 47 eV. A geometry optimized quantum mechanical self-consistent field molecular orbital treatment was employed to compute energies and structural parameters of prominent ions in the doubly charged ion mass spectra of acetylenic compounds.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210180704
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  • 19
    Digitale Medien
    Digitale Medien
    Evidence for long-lived excited states of [CnH2]2+ carbodications (1986)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 21 (1986), S. 69-75 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The energetics, structures, stabilities and reactivities of[CnH2]2+ ions have been investigated using computational methods and experimental mass spectrometric techniques. Spontaneous decompositions of [CnH2]2+ into [CnH]+ + H+ products, observed for ions with odd-n values, have been explained by invoking the formation of excited triplet states. Even-n [CnH]+ ions possess triplet ground states with low-lying excited states, whereas odd-n ions have triplet states with energies several eV above ground singlet states. Radiationless transitions of vibrationally excited long-lived triplet state ions into singlet state continua are suggested as possible mechanisms for spontaneous deprotonation processes of odd-n [CnH2]2+ ions. Evidence for these long-lived excited states has been obtained in bimolecular single electron transfer reactions.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210210205
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  • 20
    Digitale Medien
    Digitale Medien
    Positive and negative methanol cluster ions using a direct fast atom bombardment technique (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 26 (1991), S. 892-898 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Positive and negative cluster ions in methanol have been examined using a direct fast atom bombardment (FAB) probe technique. Positive ion (CH3OH)IIH + clusters with n = 1-28 have been observed and their clusters are the dominant ions in the low-mass region. Cluster-ion reaction products (CH3OH)II(H2O)H+ and (CH3OH)II(CH3OCH3)H+ are observed for a wide range of n and the abundances of these ions decrease with increasing n. The negative ion (CH3OH)II(CH3O)- clusters are also readily observed with n = 0-24 and these form the most-abundant negative ion series at low n. The (CH3OH)II(CH2O)-, (CH3OH)II(HIIO)(CH2O)- and (CH3OH)II(H2OXCH3O)- cluster ions are formed and the abundances of these ions approach those of the (CH3OH)II(CH3O)- ion series at high n. Cluster-ion structures and energetics have been examined using semi-empirical molecular orbital methods.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210261016
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