Appearance Potentials of Metastable Molecular Ions

1967 ◽  
Vol 22 (1) ◽  
pp. 40-47 ◽  
Author(s):  
I. Hertel ◽  
Ch. Ottinger
Keyword(s):  
Internal Energy ◽  
Rate Constant ◽  
Molecular Ions ◽  
Energy Scale ◽  
Constant Density ◽  
Fragment Ions ◽  
Linear Threshold ◽  
Primary Fragmentation ◽  
Order Of Magnitude ◽  
Slow Rise

Differences between the appearance potentials of fragment ions formed a few μ secs after the ionization (so-called metastables) and normal fragment ions were measured. It is shown, however, that no immediate meaning regarding the primary fragmentation mechanism can be attached to these quantities. Instead, the experimental ionization curves of metastable and normal fragments were explained by a theoretical model which assumes 1) a linear threshold law, 2) a linear relation between the logarithm of the rate constant and the internal energy in the molecular ion, and 3) a constant density of populated states on the energy scale. In the case of HCN loss from benzonitrile ions, an excellent fit between the experimental and theoretical curves can then be achieved if it is assumed that an increase of 0.65 eV internal energy increases the rate constant by one order of magnitude. This is a surprisingly slow rise of k (E), compared with the few existing calculations in other cases.

Unimolecular Gas-Phase Reactions of Diethyl Phthalate, Isophthalate, and Terephthalate upon Electron Ionization

2003 ◽  
Vol 56 (5) ◽  
pp. 473 ◽  
Author(s):  
Susumu Tajima ◽  
Masashi Mamada ◽  
Satoshi Nakajima ◽  
Yutaka Takahashi ◽  
Nico M. M. Nibbering
Keyword(s):  
Gas Phase ◽  
Molecular Ions ◽  
Ion Source ◽  
Electron Ionization ◽  
Diethyl Phthalate ◽  
Gas Phase Reactions ◽  
Fragment Ions ◽  
Metastable Fragmentation ◽  
Primary Fragmentation ◽  
Ion Kinetic Energy

Unimolecular gas-phase reactions of diethyl phthalate (1), isophthalate (2), and terephthalate (3), upon electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and deuterium labelling. The metastable molecular ions (1)+ decompose to give exclusively the ions m/z 176 ([M – CH3CH2OH]+) and not the ions by the loss of CH3CH2O as proposed earlier in the literature. The metastable molecular ions (2)+ and (3)+ fragment differently from (1)+ and lead not only to the formation of the major fragment ions m/z 194 ([M − CH2CH2]+) via a McLafferty rearrangement but also to minor fragment ions m/z 193 ([M – CH2CH3]+).Yet, molecular ions decomposing in the ion source all show as primary fragmentation channel the loss of CH3CH2O to give the ions at m/z 177, which further dissociate to give the ions at m/z 149 through the loss of C2H4 or CO, indicating the resulting ions are +COC6H4COOH and +C6H4COOCH2CH3. The +COC6H4COOH ions decompose into the m/z 121, 93, and 65 ions by the consecutive losses of three carbon monoxide molecules, respectively. Prior to the second CO loss, a migration of the OH group to the benzene ring occurs. During the metastable fragmentation of the +C6H4COOCH2CH3 ions no ethoxy migration occurs, in contrast to the methoxy migration taking place in the metastable decomposition of the lower homologue +C6H4COOCH3 ions.

Appearance Energies and Calculated Partial Mass Spectra of (23-), (2,4-) and (2,5-)Dimethylaniline Isomers

1983 ◽  
Vol 38 (10) ◽  
pp. 1084-1087 ◽  
Author(s):  
F. H. Abd El-Kader ◽  
H. M. Ahmed
Keyword(s):  
Energy Range ◽  
Internal Energy ◽  
Energy Dependence ◽  
Mass Spectra ◽  
Critical Energy ◽  
Molecular Ions ◽  
Fragment Ions ◽  
Kinetic Shift

Abstract The ionization and appearance energies for the molecular and fragment ions, respectively, of the three dimethylaniline isomers are reported. Breakdown graphs have been constructed expressing the energy dependence of the fragmentation of the isomeric molecular ions covering the internal energy range from threshold to approximately 10 eV. The kinetic shift and the critical energy for the fragments (M-H)+ and (M-CH3)+ ions are also calculated.

Continuous flow fast atom bombardment mass spectrometry of mononucleotides and their metal complexes

1989 ◽  
Vol 67 (5) ◽  
pp. 910-920 ◽  
Author(s):  
M. J. Bertrand ◽  
V. Benham ◽  
R. St-Louis ◽  
M. J. Evans
Keyword(s):  
Mass Spectrometry ◽  
Continuous Flow ◽  
Fast Atom Bombardment ◽  
Aqueous Media ◽  
Molecular Ions ◽  
Fragment Ions ◽  
Low Concentrations ◽  
Metal Adducts ◽  
Matrix Concentration

The mass spectra of mononucleotides and their metal adducts Na, K, Mg, Ca, Ni, Co, Cu, and Zn of guanosine 5′-monophosphate (5′-GMP) as well as H, Na, and Mg of adenosine 5′-monophosphate (5′-AMP) and H and Ni of inosine 5′-monophosphate (5′-IMP) have been obtained in low concentrations of matrix in water using continuous-flow fast atom bombardment. The results indicate that this technique is suitable for the analysis of these complexes in aqueous media and yields spectra that are highly characteristic of the compounds analyzed. Parent-molecular ions and structurally significant fragment ions are observed for all compounds studied and the different binding sites for the metal on the nucleotides can be isolated from the fragment ions. Experimental parameters influencing the quality of the spectra such as flow rate, matrix concentration, matrix nature, and analyte concentration have been studied and optimized. For the thirteen compounds studied, it appears that continuous-flow FAB is superior to conventional FAB and that good quality spectra can be obtained with as little as 0.5% of added matrix thus minimizing spectral interferences. Keywords: continuous flow FAB, FAB MS, mass spectrometry, nucleotides, metal-nucleotides.

The Formation of Molecules in Three Atom Collisions using the Eikonal Approximation

1976 ◽  
Vol 31 (12) ◽  
pp. 1489-1499
Author(s):  
E. Czuchaj
Keyword(s):  
Experimental Data ◽  
Numerical Calculation ◽  
Rate Constant ◽  
Recombination Rate ◽  
Eikonal Approximation ◽  
New Approach ◽  
Order Of Magnitude ◽  
Recombination Rate Constant ◽  
Good Agreement

Abstract A new approach to the calculation of a teratomic recombination rate constant k(T) has been dem-onstrated. An expression for k(T) has been obtained in the eikonal approximation. The numerical calculation has been carried out for the Rb*-Xe system. Good agreement in the order of magnitude between the present results and the experimental data of Carrington et al. has been obtained.

Rearrangements in the Molecular Ions of Some ortho-Substituted Schiff Bases

1993 ◽  
Vol 46 (6) ◽  
pp. 895 ◽  
Author(s):  
T Blumenthal ◽  
M Dosen ◽  
RG Gillis ◽  
QN Porter
Keyword(s):  
Kinetic Energy ◽  
Schiff Bases ◽  
Molecular Ions ◽  
Energy Spectra ◽  
Supporting Evidence ◽  
Deuterium Labelling ◽  
Methyl Group ◽  
Molecular Ion ◽  
Fragment Ions ◽  
Ion Kinetic Energy

Under electron ionization conditions, the ortho-substituted Schiff bases N-benzylidene-o-toluidine (1a), N-(o-methylbenzylidene)aniline (1b), N-salicylideneaniline (1c) and N-(o-methoxybenzylidene)aniline (1d) give fragment ions which have been shown by collision-activated mass-analysed ion kinetic energy spectra to have the structure of the protonated molecular ions of indole (2), benzofuran (3), and 1,2-benzisoxazole (4). The molecular ion of N-(o-methylbenzylidene)-o-toluidine (1f) gives as fragment ions not only the protonated molecular ion (2) of indole and the tropylium ion but also the molecular ion of anthracene. Attempts to find supporting evidence for a mechanism for this rearrangement by deuterium labelling of a methyl group in (1b), such as (1g), have been unsuccessful.

Mass spectral investigations on selenium compounds. II. The behaviour of meta-and para-substituted benzeneseleninic acids and of meta-nitrophenyl selenocyanate under electron impact

1982 ◽  
Vol 35 (7) ◽  
pp. 1365 ◽  
Author(s):  
A Benedetti ◽  
C Preti ◽  
L Tassi ◽  
G Tosi
Keyword(s):  
Mass Spectrometry ◽  
Mass Spectrum ◽  
Electron Impact ◽  
Molecular Ions ◽  
Selenium Compounds ◽  
Molecular Ion ◽  
Mass Spectral ◽  
Low Intensity ◽  
Fragment Ions

Substituted benzeneseleninic acids of the type XC6H4SeO2H (X = m-Cl, p-Cl, m-Br, p-Br, p-Me, m-NO2, p-NO2) have been investigated by mass spectrometry. The fragmentation modes and the fragment ions are discussed and compared with those obtained from the mass spectrum of m-nitro-phenyl selenocyanate, O2NC6H4SeCN. Generally, as regards the acids, besides very weak peaks due to the molecular ions, a number of peaks at higher mass numbers and of greater intensity is observed; these peaks are in multiplets typical of the presence of two selenium atoms, and they correspond to the disubstituted diphenyl diselenides of the type XC6H4SeSeC6H4X. m-Nitrophenyl selenocyanate shows an intense molecular ion peak and the relative fragmentation, while the peak due to the diselenide is of very low intensity.

Negative Ionen durch Elektronenstoß aus organischen Nitroverbindungen, Äthylnitrit und Äthylnitrat

1967 ◽  
Vol 22 (5) ◽  
pp. 700-704
Author(s):  
K. Jäger ◽  
A. Henglein
Keyword(s):  
Electron Impact ◽  
Negative Ions ◽  
Molecular Ions ◽  
Ion Source ◽  
Negative Ion ◽  
Electron Affinities ◽  
Low Intensity ◽  
Ion Molecule Reactions ◽  
Fragment Ions ◽  
Product Ions

Negative ion formation by electron impact has been studied in nitromethane, nitroethane, nitrobenzene, tetranitromethane, ethylnitrite and ethylnitrate. Appearance potentials, ionization efficiency curves and kinetic energies of negative ions were measured by using a Fox ion source. The electron affinities of C2H5O and of C (NO2)3 are discussed as well as the energetics of processes which yield NO2-. The electron capture in nitrobenzene and tetranitromethane leads to molecular ions [C6H5NO2~ in high, C (NO2)4 in very low intensity] besides many fragment ions. A number of product ions from negative ion-molecule reactions has also been found.

Time-Resolved Transport of Electrons and Holes in Conjugated Polymers

1999 ◽  
Vol 561 ◽  
Author(s):  
D. Pinner ◽  
R. H. Friend ◽  
N. Tessler
Keyword(s):  
Conjugated Polymers ◽  
Temporal Evolution ◽  
Exponential Tail ◽  
Time Resolved ◽  
Light Emitting ◽  
Turn On ◽  
Initial Rise ◽  
Order Of Magnitude ◽  
Slow Rise ◽  
Polymer Light Emitting Diodes

ABSTRACTDetailed experimental and theoretical analysis of the pulsed excitation of polymer light emitting diodes is presented. We find a set of universal transient features for different device configurations which can be reproduced using our phenomenological numerical model. We find that the temporal evolution of the electroluminescence can be characterised by five main features: i) a delay followed by; ii) fast initial rise at turn-on followed by; iii) a slow rise (slower by at least one order of magnitude); iv) fast modulation (<15ns, unresolved) at turn-off followed by v) a long-lived exponential tail. We suggest a method for extracting mobility values which is found to be compatible with CW drive schemes. Mobilities for holes and electrons are extracted for a poly(p-phenylenevinylene) co-polymer and poly(di-octyl fluorene).

Mass spectrometry of some furanocoumarins

1979 ◽  
Vol 57 (15) ◽  
pp. 1995-2003 ◽  
Author(s):  
Sheng-Yuh Tang ◽  
John C. Mcgowan ◽  
Marsha Singh ◽  
Paul Galatsis ◽  
Brian E. Ellis ◽  
...  
Keyword(s):  
Electron Impact ◽  
Mass Spectra ◽  
Kinetic Energy Release ◽  
Molecular Ions ◽  
Structural Isomers ◽  
Molecular Systems ◽  
Fragment Ions ◽  
Fragmentation Mechanisms ◽  
Impact Ionisation ◽  
Partial Success

The mass spectra of two isomeric methoxyfuranocoumarins have been investigated using electron-impact ionisation. Unambiguous distinction between the two isomers is possible through a combination of conventional mass spectra with collision-induced dissociations of the molecular ions and of selected fragment ions. The fragmentation mechanisms of these and related molecular systems were investigated in an attempt to identify the fate of each oxygen atom under electron-impact conditions. To this end, 2-pyrone, benzpyrone (coumarin), benzofuran, and some of its structural isomers were synthesised and studied via metastable spectra, collisionally activated spectra, appearance potentials, and kinetic energy release. Only partial success was achieved in this investigation, but it was possible to write a mechanistic scheme consistent with the present findings and literature data. If valid, this scheme permits identification of two of the four oxygen atoms in the methoxyfuranocoumarins.

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