Peter C. Burgers

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.

Isomeric distonic and H-bridged [C2H6O]+ radical cations

Abstract Ab initio molecular-orbital calculations (SD Cl/6-31G★★ confirm that the most stable [C2H6O]+ isomer is the distonic ion [CH2CH2OH2]+. Mass spectrometric measurements give ΔH0f, 298 = 732 ± 5 kJ mol−1. This ion interconverts with a yet-unidentified isomer, [CH2CH⋯H⋯OH2]+, a hydrogen-bridged water/ethene radical cation complex. The latter ion lies in a shallow well, 38 kJ mol−1 above [CH2CH2OH2]+ and 41 kJ mol−1 below the dissociation into [C2H4]+ and H2O. Above the interconversion barrier the isomers behave like ethene-ion/water-dipole complexes in which the dipole can move all around the ion. This behaviour may relate to the very small kinetic energy release in the dissociation.

Fragmentation rate constants and appearance energies for reactions having a large kinetic shift and the energy partitioning in their metastable decomposition

Abstract Appearance energies (AE) of primary daughter ions for reactions possessing marked kinetic shifts have been measured using energy selected electrons and metastable peak observations. The time scales and limiting threshold rate constants corresponding to these measurements have been estimated by comparisons with results from photoion-photoelectron coincidence experiments. The dependence of the fraction of excess internal energy, E ‡, released as kinetic energy of the products, T , on the magnitude of E ‡ is described. In general, the fraction increases with decrease of E ‡ and cannot adequately be described by the empirical equation of Haney and Franklin, E ‡ = 0.44 T × (number of vibrational degrees of freedom).

The collisionally induced dissociations of the carboxyl and formate positive and negative ions

Abstract The formate positive ion, [HCOO]+, is produced by the collisionally induced charge reversal of the corresponding negative ion. Those [HCOO]+ ions having insufficient energy (

HOC+: Laboratory observation of a proposed interstellar species

Abstract The ion [HOC + ] together with some [HC + O] is generated by the dissociative ionisation of CD 3 OH. Collisional activation mass spectral characteristics of the two isomers are reported. Δ H f ([HOC + ]) is estimated to be 930 ± 20 kJ mol −1 .

The need for adequate thermochemical data for the interpretation of fragmentation mechanisms and ion structure assignments

Abstract A knowledge of ionic heats of formation is essential to the full interpretation of mass spectrometric data. Empirical methods for estimating ΔH f [Ion] +· values are described.

Characterization of ion-dipole complexes by collisional activation and collisional ionization spectrometry

Abstract Complexes between a radical cation and a dipole molecule are taking their place beside the conventional isomeric ion structures in mass spectra. Complexes of H2O, NH3, H2S, PH3, HF, HCl, HBr, CH3CN and CH3NC with CH2+ ions and a number of higher homologues are formed via dissociative ionization and/or ion molecule reactions. Structures were established by Collisional Ionization and Activation Mass spectra. A number of stabilities established by measurements and quantum mechanical calculations show that they fall in the range of those of conventional isomers and that conversion barriers are generally high.

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.