C. E. C. A. Hop

Fragmentation characteristics of the unstable [CH3 CO] radicals generated by neutralization of [CH3CO]+ cations

Abstract The stability and fragmentation characteristics of [CH3 CO] radicals, generated by vertical charge exchange between acetyl cations and permanent gases or metal vapours (He, Xe, NO, Cd, Na and K), were examined mass spectrometrically. Two dissociation reactions were observed, the losses of CH 3 and H . The H loss reaction, the higher energy dissociation, became of greater importance as the exothermicity of the charge exchange was increased. Based on the analysis of the kinetic energy releases it was concluded that these decompositions arose from the population of two excited states of the [CH3 CO] radical.

The isomeric ions produced by the gas phase protonation of HNCO and HCNO

Abstract Ab initio molecular orbital theory calculations combined with mass spectrometric experiments show that the gas phase protonation of HNCO yields [H 2 NCO] + (Δ H f 0 =672 kJ mol −1 ), whereas HCNO produces [HCNOH] + (Δ H f 0 =990 kJ mol −1 ). The proton affinity of fulminic acid, HCNO, is estimated to be 758 kJ mol −1 .

Neutralization-reionization of CH4+•: At which stage does fragmentation occur?

Abstract Experimental (collision-induced dissociative ionization (CIDI) and neutralization-reionization mass spectrometry (NRMS)) and theoretical (ab initio molecular orbital) procedures were used to examine the origin of the fragmentation observed in NRMS experiments on the methane radical cation. Both theory and experiment indicate that in NRMS experiments involving neutralization by species of high ionization energy (e.g. Hg or Xe), the fragmentation occurs largely at the reionization rather than the neutralization stage. The reverse is true for the strongly exothermic neutralization with Na. Corresponding experiments [C 2 H 6 ] +• ions showed similar behaviour.

The stability of [CCl4]+·, [Cl2CClCl]+·, their dications, and neutral counterparts

Electron impact ionization of tetrachloromethane has been shown to produce stable [CCl4]+· ions; their heat of formation is ⩽ 237 kcal mol−1. The ylid isomer, [Cl2CClCl]+·, generated upon dissociative ionization of Cl3CCOCl, is remarkably more stable; ΔH0f([Cl2CClCl]+·) < 224 kcal mol−1. The values for both isomers are significantly lower than calculated values. The corresponding neutrals, CCl4 and Cl2CClCl, are not stable on the time and energy scale of neutralization—re-ionization experiments. Although [Cl2CClCl]2+, was calculated to be stable, it was not present in the charge-stripping mass spectrum of the ylid ion.

Translational energy spectroscopy of collisional neutralization-reionization processes

Abstract The translational energy change, Δ T [M + ] nr , undergone by fast ions in neutralization-reionization collisions was measured for a number of projectiles and collision gas combinations. The dependence of Δ T [M + ] nr on the vibrational energy content of 8 keV [H 2 ] +√ ions was investigated and discussed. From the variation in Δ T [M + ] nr for three [C 2 H 4 O] +√ and three [C 3 H 6 O] +√ isomers it could be established which of the neutral counterparts were stable and which of them rearranged before reionization. For example, neutralized [CH 2 CHOH] +√ was proposed to rearrange via a 1,2 H shift into CH 3 COH. The mechanism of the collisional reionization was investigated for various target gases. The observed translational energy changes indicated that electron transfer from the neutral projectile to the reionization target gas was not an important process in our experimental conditions.

KeV collisions of methonium ions: the properties of CH5 and [CH5]2+ and the generation of high-Rydberg fragments therefrom

Abstract Neutralization reionization mass spectrometry (NRMS) experiments were carried out with [CH 5 ] + , [CD 5 ] + , and [CD 4 H] + ions of 8 keV translational energy using a variety of neutralization and reionization target gases. Careful analysis of the spectra showed that, contrary to earlier reports, (meta)stable CH · 5 (and isotopomer) species were not generated by charge transfer neutralization of the fast ions beams. Kinetic energy spectra of ionic fragments from collisions between [CD 5 ] + ions of 9.9 keV kinetic energy and O 2 target gas were used to study the dissociative states of the [CD 5 ] + and [CD 5 ] 2+ ions. Metastable high-Rydberg species arising from 9.9 keV [CD 5 ] + /He collisions were selectively field ionized and the kinetic energy spectra of the resulting ions obtained. Mechanisms for the generation of the high-Rydberg fragments were established.