Isotope Effects on Metastable Transitions. IV. Isotopic Methanols

Abstract

Metastable transitions were studied in the mass spectra of methanol and deuterated methanols in a sector mass spectrometer. The relative abundances of the various metastable ions at 70eV were determined. The intensities are in good agreement with those obtained employing a double‐focussing instrument operating in the metastable mode. There is a strong isotope effect on the intensity of the anomalous parent‐ion metastable transition. This transition and the one leading to a “flat top” metastable peak were studied carefully. Appearance potentials were determined for the ions involved, by the RPD method and for the metastables themselves by conventional techniques. Metastable ion decay curves were obtained using an improved pulsed ion source. The results are discussed in terms of the quasi‐equilibrium theory of mass spectra.

Translational energy release: Experiment and theory. H2 elimination reactions of small gas phase ions, and correspondence to HH bond activation

“…In 1987, it was proved experimentally that the product ion has the formyl ion structure, and not the isoformyl cation structure (Wijenberg et al, 1987). Measurements of the appearance energy of the HCO ions formed from metastable CH 2 OH ions have established that the critical energy of the process is E 0 325 AE 15 kJ mol À1 (Lifshitz Shapiro, & Sternberg, 1969a;Williams & Hvistendahl, 1974b;Uggerud, 1979;Momigny, Wankenne, & Krier, 1980;Nishimura et al, 1980;Wijenberg et al, 1987). The corresponding reverse critical energy is 200 AE 15 kJ mol À1 .…”

Mass spectrometry

“…In the mass spectra of CD3-CH3 and CzHe, 54 metastable peaks are observed for the former and 19 for the latter (1232). In this system (1233) and in isotopic methanols (1234), an isotope effect on metastable transitions is observed on both the intensity and kinetic-energy release of the molecularhydrogen elimination from the parent. The energetics of formation of metastable peaks in the mass spectra of N2 and NO have been studied {1235).…”

Reaction dynamics of the four-centered elimination CH2OH+→CHO++H2: Measurement of kinetic energy release distribution and classical trajectory calculation

“…36,37,39,80 In deuterium labelling experiments, 60,61 it was found that the reaction occurred via 1,2-elimination process. That is, CD 2 OH ϩ and CH 2 OD ϩ lost HD only in unimolecular dissociation.…”