Experiments on Electron-Impact Ionization of Atomic and Molecular Ions

2005 ◽  
Author(s):  
M. E. Bannister
Keyword(s):  
Electron Impact ◽  
Impact Ionization ◽  
Electron Impact Ionization ◽  
Molecular Ions

Electron Impact Ionization in Helium Nanodroplets:  Controlling Fragmentation by Active Cooling of Molecular Ions

2004 ◽  
Vol 126 (36) ◽  
pp. 11283-11292 ◽  
Author(s):  
William K. Lewis ◽  
Brian E. Applegate ◽  
Judit Sztáray ◽  
Bálint Sztáray ◽  
Tomas Baer ◽  
...  
Keyword(s):  
Electron Impact ◽  
Impact Ionization ◽  
Electron Impact Ionization ◽  
Molecular Ions ◽  
Helium Nanodroplets ◽  
Active Cooling

The chemistry of peptides related to metabolites of Trichoderma Spp. 3. An unusual dehydration reaction of 2-methylalanine peptides after electron impact ionization

1986 ◽  
Vol 64 (2) ◽  
pp. 277-284 ◽  
Author(s):  
W. D. Jamieson ◽  
A. Taylor
Keyword(s):  
Electron Impact ◽  
Impact Ionization ◽  
Reaction Rates ◽  
Electron Impact Ionization ◽  
Molecular Ions ◽  
Dehydration Reaction ◽  
Ionization Source ◽  
Trichoderma Spp ◽  
C Terminus ◽  
Free Region

Peptides of 2-methylalanine, where this residue is not the C-terminus, give molecular ions of low abundance on electron impact ionization, but abundant ions are formed by loss of the elements of water from the molecular ion. The dehydration reaction does not occur in permethylated derivatives, nor under the milder ionization conditions in the chemical ionization source. The reaction does not appear to be time or temperature dependent, but depends on the steric hindrance of the NH group of the 2-methylalanine residue. The reaction occurs at sites where 2-methylalanine is not the C-terminal amino acid. In the cases of two pentapeptides where the dehydration reaction was of high probability, the correct sequence was found by semi-quantitative measurements of reaction rates in the first field-free region of a double focussing mass spectrometer.

Electron-Impact Ionization of Mandelic Acid and Mandelic Acid Methyl Ester as Prototypes for the C6H5CH(OH)-X System: Ionization and Appearance Energies, Activation Energies and Enthalpies of Formation

2005 ◽  
Vol 11 (4) ◽  
pp. 371-380 ◽  
Author(s):  
Joachim Opitz
Keyword(s):  
Methyl Ester ◽  
Electron Impact ◽  
Mandelic Acid ◽  
Impact Ionization ◽  
Acid Methyl Ester ◽  
Electron Impact Ionization ◽  
Molecular Ions ◽  
Enthalpies Of Formation ◽  
Ionization Mass ◽  
Acid Methyl

Electron-impact ionization mass spectra, the decay of metastable ions, ionization and appearance energies and bond energies, as dissociation energies, are reported for mandelic acid (MA) and mandelic acid methyl ester (MAME) . An ionization energy of 8.55 eV was obtained for both compounds. For the formation of C6H5+ ions, appearance energies of 14.25 eV or 14.40 eV were determined for MA or MAME, respectively. On the main fragmentation route from molecular ions to these C6H5+ ions, an activation energy of (1.1±0.1)eV in excess of the calculated total reaction enthalpy was found for the elimination of CO from the prominent C7H7O+ ions to C6H7+ ions, involving the transfer of two H-atoms. The second (minor) fragmentation route via C7H6O+ions resembles the benzaldehyde decomposition pathway and the individual steps were found to be near to their calculated thermochemical reaction enthalpies. Gas-phase enthalpies of formation of (–4.652±0.3 eV) [≡ (–448.8±30) kJ mol−1] for MA and (–4.243±0.3) eV [≡ (–409.4±30) kJ mol−1] for MAME are derived, based on the appearance energy of their C7H7O+ ions at m/z 107 and the formation enthalpy adopted from protonated benzaldehyde. The results are compared with data for benzylalcohol.

scholarly journals Low-energy electron-impact ionization of helium

1998 ◽  
Vol 57 (5) ◽  
pp. R3161-R3164 ◽  
Author(s):  
Igor Bray ◽  
Dmitry V. Fursa ◽  
J. Röder ◽  
H. Ehrhardt
Keyword(s):  
Electron Impact ◽  
Impact Ionization ◽  
Electron Impact Ionization ◽  
Low Energy ◽  
Energy Electron ◽  
Low Energy Electron
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