Alexander A. Mommers

Neutral products of ion fragmentations: HCN and HNC identified by collisionally induced dissociative ionization

Abstract Collisionally induced dissociative ionization of HCN and HNC permits their identification as neutral products in the fragmentations of ionized pyridine and aniline respectively.

The mass spectrometry of neutral species produced from mass-selected ions by collision and by charge exchange. Experiments with tandem collision gas cells

The neutralisation—reionisation mass spectra (NRMS) of a number of organic cations have been measured. Neutralisation was achieved by electron transfer from Xe atoms in the first of two collision cells in the second field-free region of a double focussing mass spectrometer of reversed geometry. Reionisation took place by collisional excitation with He atoms in the second cell; ions passing beyond the first cell were prevented from entering the second by an ion beam deflector electrode. The NRMS of benzene and acetic acid molecular ions were similar to the normal electron impact (EI) mass spectra and collisional activation (CA) mass spectra of the two molecules. Acetic acid molecules generated from the unimolecular dissociation of the proton bound dimer [CH3COOH]2H+ had a collision-induced dissociative ionisation (CIDI) mass spectrum closely similar to that derived from EI. Effects arising from neutral species generated by normal collisionally induced fragmentations of the ions in the first cell were shown to be small. The significant differences between the EI, CA and NRMS of methyl formate and its CIDI mass spectrum, derived similarly from [HCOOCH3]2H+, were considered indicative of the presence of rearranged molecular ions among those sampled by CA, some, but not all, of which produced stable neutral species. The NRMS of the acetyl, carboxyl and formyl cations were measured under conditons of good energy resolution. The observations were interpreted in terms of the dissociation characteristics of the intermediate free radicals, each of which underwent sufficient collisional energisation during the electron transfer from Xe, to decompose by simple bond cleavages. For , the results were in qualitative agreement with recent estimates for the energy barriers for the competing reactions yielding and .

Four isomeric [C, H3, O2]+ ions

The isomeric ions [HC(OH)2]+, carbonyl oxygen-protonated formic acid [H2C(O+)OH], carbon-protonated formic acid, the methylene hydroperoxy cation, [CH2OOH]+, and the methylperoxy cation, [CH3OO]+, have been characterised by their collisional activation mass spectra, [HC(OH)2]+ and [CH2OOH]+ were generated by dissociative ionisation whereas the other two ions were produced by collisionally induced charge reversal of the corresponding anions. The fragmentations of [HC(OH)2]+ to yield [HC+ O] and [H3O]+ proceed via a common rate-determining energy barrier.

Photon emissions from N2·+ ion beam-target gas collisions in a modified commercial sector mass spectrometer

Abstract Experiments are reported in which radiative emissions from 8 keV N2·+ projectile ion—target gas (He, N2, O2 and CO2) collisions in the third field-free region of a modified VG ZAB-2F mass spectrometer (BEE geometry) were detected and analyzed using a scanning grating monochromator. The emission spectra between 180 and 680 nm were characterized by the N2·+ (B2Σu+ → X2Σg+) electronic transition and, when N2 and O2 were the targets, the C 3Πu → B 3Πg second positive system in N2. Fragment N+ emissions were also observed. In addition to the projectile emissions, ionized target gas and even target fragment emissions were present with all targets except helium. Observations made 0.05–0.17 μs after the collision event were similar to those described above, but lacking target gas emissions. Qualitative information concerning the trends in post-collission emission, studied with 18 target gases, was obtained using wavelength cut-off filters. The results were consistent with the above spectral assignments and trends observed in collision induced dissociation mass spectrometry.

The isotope effect associated with the loss of an oxygen atom from [CO2D]+ ions

Abstract The metastable loss of O from [COOH] + ions produces the formyl cation [HCO] + , whereas loss of O from [COOD] + yields [DCO] + and [COD] + . The energy partitioning for these reactions is explained in terms of transition state geometries.

Two new stable[C3H8O]+˙ isomers: the radical cations [C3H6OH2]+˙

Two new [C3H8O]+˙ ions have been assigned the structures [ĊH2CH2CH2OH2] and [CH3CHCH2OH2]+˙ and were characterised by their metastable ion and collisional activation mass spectra; their heats of formation were measured as 714 ± 5 and 721 ± 5 kj mol–1, respectively.