Dissociative electron attachment to unstable molecules and slow fragmentation of metastable molecular anions

Recent experimental investigations of dissociative electron attachment to unstable molecules and free radicals are reviewed along with observations of metastable negatively charged ions. Measurements have been made with a time-of-flight mass spectrometer in Belfast and also, for metastable ions, with a double focussing twin field mass spectrometer in Innsbruck. Electron attachment to unstable CS, for example, was found to be similar to electron attachment to the valence isoelectronic CO molecule with observation of S− and C− ions just above the thermodynamic threshold for S− + C (P) at 5.43 eV, C− + S at 6.40 eV and S− + C(D) at 6.70 eV with peak cross sections of ∼ 0.025 Å, 0.002 Å and 0.003 Å respectively. Slow fragmentation of metastable SF−∗ 6 formed in low energy electron attachment to SF6 has been observed on microsecond timescales in competition with autodetachment; processes SF−∗ 6 → SF− 5 + F and SF−∗ 6 → SF6 + e − respectively. Fragmentation of metastable anions of benzene derivatives, such as 2,4-dinitro-toluene [CH3.C6H3(NO2)2], has also been observed on microsecond timescales.