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Using a Nier-type electron impact ion source in combination with a double focusing two sector field mass spectrometer, partial cross sections for electron impact ionization of acetylene are measured for electron energies up to 1000 eV. Discrimination factors for ions are determined using the deflection field method in combination with a three-dimensional ion trajectory simulation of ions produced in the ion source. Analysis of the ion yield curves obtained by scanning the deflectors allows the assignment of ions with the same mass-to-charge ratio to specific production channels on the basis of their different kinetic energy distributions. This analysis also allows to determine, besides kinetic energy distributions of fragment ions, partial cross sections differential in kinetic energy. Moreover a charge separation reaction, the Coulomb explosion of the doubly charged parent ions C2H2++ into the fragment ions C2H+ and H+, is investigated and its mean kinetic energy release (=3.88 eV) is deduced. [ABSTRACT FROM AUTHOR]

We have measured the kinetic energy released in the unimolecular dissociation of fullerene ions, Cn+→Cn-2++C2, for sizes 42≤n≤90. A three-sector-field mass spectrometer equipped with two electric sectors has been used in order to ensure that contributions from isotopomers of different masses do not distort the experimental kinetic energy release distributions. We apply the concept of microcanonical temperature to derive from these data the dissociation energies of fullerene cations. They are converted to dissociation energies of neutral fullerenes with help of published adiabatic ionization energies. The results are compared with literature values. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

C[sub 3]H[sup 2+, sub 5], formed by electron impact ionization of propane, undergoes metastable decay into C[sub 2]H[sub 2, sup +] + CH[sub 3, sup +]. We have monitored this reaction in a magnetic mass spectrometer of reversed geometry that is equipped with two electric sectors (BEE geometry). Three different techniques were applied to identify the fragment ions and determine the kinetic-energy release (KER) of spontaneous Coulomb explosion of C[sub 3]H[sup 2+, sub 5] in the second and third field free regions of the mass spectrometer. The KER distribution is very narrow, with a width of about 3% [root-mean square standard deviation]. An average KER of 4.58 ± 0.15 eV is derived from the distribution. High level ab initio quantum-chemical calculations of the structure and energetics of C[sub 3]H[sup 2+, sub 5] are reported. The activation barrier of the reverse reaction, CH[sub 3, sup +] + C[sub 2]H[sub 2, sup +] (vinylidene), is computed. The value closely agrees with the experimental average KER, thus indicating that essentially all energy available in the reaction is partitioned into kinetic energy. [ABSTRACT FROM AUTHOR]

Neon dimer ions undergo spontaneous dissociation (metastable decay) several microseconds after formation by electron impact ionization of neon clusters. In this contribution we compare the kinetic energy release distribution (KERD) of the previously reported isotopomer 20Ne2 + with that of 22Ne2 +. The heavy isotopomer shows the same two components in the KERD as the lighter ones. However, the high-energy component that is due to electronic pre-dissociation is reduced in intensity. The decrease is attributed to a reduced predissociation rate from the II(1/2u) state into I(3/2u). [ABSTRACT FROM AUTHOR]

Neon dimer ions undergo spontaneous dissociation (metastable decay) several microseconds after formation by electron impact ionization of neon clusters. In this contribution we compare the kinetic energy release distribution (KERD) of the previously reported isotopomer 20Ne2 + with that of 22Ne2 +. The heavy isotopomer shows the same two components in the KERD as the lighter ones. However, the high-energy component that is due to electronic pre-dissociation is reduced in intensity. The decrease is attributed to a reduced predissociation rate from the II(1/2u) state into I(3/2u). [ABSTRACT FROM AUTHOR]

Abstract: We have measured the kinetic energy release distributions for unimolecular C2 loss from singly and multiply charged endohedral La@C80 z+ and La@C80 z+ ions for charge states z =1–3. Using finite heat bath theory, we deduce the dissociation energies for loss of C2. The charge state z has no statistically significant effect on the dissociation energies. The dissociation energies of endohedral fullerene ions are larger than those of the corresponding empty fullerene ions by a few tenths of an electron volt, but the differences are barely statistically significant. The small differences also imply that the complexation energies of La@C n z+ and La@C n −2 z+ are identical within the experimental errors, for n =80 and 82 and all charge states. [Copyright &y& Elsevier]

Abstract: Metastable fractions for the dissociation of fullerene cations have been measured in a three-sector-field mass spectrometer. They have been determined with the same experimental setup as the kinetic energy release data published recently. A statistical model which includes cooling by radiation as required by the timescale of the experiment is used to deduce dissociation energies from the metastable fractions. The results are compared with values extracted from our kinetic energy release data and other experiments. [Copyright &y& Elsevier]

The high resolution double focusing mass spectrometer of reversed Nier-Johnson geometry was used in research of ionization and fragmentation processes of ethanol molecules C2H5OH. Using the mass-analyzed ion kinetic energy technique, fragmentation paths and kinetic energy release distributions were examined for the four fragmentation reactions: C2H6O+ → C2H5O+, C2H6O+→C2H3O+, CH3O+→CH2O+ and CH3O+ → CHO+. For all fragment ions from these reactions mean values of kinetic energy release ∊were determined. We calculated mean values of ∊as 22.70 meV, 62.15 meV, 30.25 meV, and 117.20 meV for C2H5O+, C2H3O+, CH2O+, and for CHO+ ions, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Metastable ions C3HnN+ (n =1, 2 or 3) and C2H2 + produced by electron impact on the neutral C3H3N (acrylonitrile) undergo metastable decay reactions resulting in the fragment ions C3HmN+ (m =1, 2) or C2H2 +. We have monitored these reactions in a double focusing mass spectrometer of reversed B-E geometry. To identify the fragment ions and determine their kinetic energy release distribution (KERD), the mass-analyzed ion kinetic energy (MIKE) scan technique was utilized. For the above mentioned ions we obtained average KER values ranging from 9 up to 23meV. Moreover, the fractions of decaying ions were measured. We have found the existence of two states of the metastable C2H2 + ion, one with a short life time of about 0.27μs and the other one which is most likely a completely stable ion state. [Copyright &y& Elsevier]

Abstract: Doubly charged ions produced by electron impact ionization of toluene undergo metastable decomposition. We have determined decay channels for and the average kinetic energy release (KER) by applying the MIKE scan technique. We observe several reactions that have not been reported previously, including H2 elimination from . The KER distribution for H2 loss shows no evidence for a reverse barrier. The average KER is <0.1 eV; it exhibits a distinct time dependence and isotope effect. On the other hand, some charge separation reactions reported previously in the literature are likely due to isotopic interference. [Copyright &y& Elsevier]

Abstract: The synthesis of silver nanoparticles via UV irradiation of AgNO3 solutions was controlled by using UV–vis absorption spectra and TEM (transmission electron microscope) images. The UV–vis absorption method is good enough for the general control of synthesis process, and TEM images give us information about size of formed species. For investigated solutions of silver nitrate in ethanol and water, we observed formation of large nanoparticles (size about 100nm) and nanorods (100nm in length). Moreover, there was effort to confirm evidence of formation of these particles by using TOF mass spectrometer. Due to laser desorption/ionization process there is only evidence of small silver nanoparticles Ag x , x ≤4 (clusters), and variety of silver compounds Ag x N y O z (x ≤5, y ≤2, z ≤3). [Copyright &y& Elsevier]

Metastable fragmentation of neon dimer ions has been investigated by measuring and analyzing high resolution kinetic energy release distributions. Data were obtained by a modified MIKE (mass-analyzed ion kinetic energy) scan technique. Due to the high energy resolution it was possible to distinguish two different reaction mechanisms in the micros time regime which produce Ne+ ions with different kinetic energy distributions. Theoretical studies based on ab initio calculations of potential energy curves allowed the assignment of the reactions to specific electronic transitions in the excited Ne2+ ion. The unusual bimodal kinetic energy release distribution arises from competition between radiative and non radiative decay of the long-lived Ne2+ II(1/2)u state.

Dissociative decay of metastable, electronically excited neon and argon dimer ions produces fragment ions with strikingly dissimilar kinetic-energy-release distributions. The distributions have been modeled based on ab initio calculations of potential energy curves. The unusual bimodal distribution observed for dissociation of Ne2+ arises from competition between radiative and nonradiative decay of the long-lived II(1/2)(u) state. For Ar2+, however, electronic predissociation is insignificant.

The effect of impurity (sodium sulfate Na2SO4; copper sulfate CuSO4; potassium ferrocyanide K4Fe(CN)6; and triammonium citrate (NH4)3C6H5O7) concentration on the positive matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectra of insulin is described. 2,5-Dihydroxybenzoic acid was used as a desorption matrix. The estimated maximum concentrations of tested salts for which no insulin signal was observed were determined., (Copyright 2001 John Wiley & Sons, Ltd.)