Formation of anion fragments from gas-phase glycine by low energy (0-15 eV) electron impact

摘要

We have measured the formation of anion fragments in gas phase glycine (H_2NCH_2COOH) via dissociative electron attachment (DEA) reactions in the 0-15 eV electron energy range, using a monochromatic electron beam and mass spectrometric detection of the negative ions. By far the most intense product observed is the closed shell glycine anion (H_2NCH_2COO)~- which appears from a low-energy resonance with a peak located at 1.4 eV and a cross section in the range 10~(-16) cm~2. The corresponding precursor ion can be characterized by electron attachment into the empty #pi# orbital of the -COOH group as recently assigned from electron transmission experiments and ab initio self-consistent field calculations [Aflatooni, Hitt, Gallup, and Burrow, J. Chem. Phys. 115, 6489 (2001)]. This precursor state is also observed to decompose (with much lower intensity) yielding a negative ion fragment with 58 amu, which is attributed to anions of the stoichiometric composition H_2C_2O_2~- or H_4C_2NO~=. A further prominent DEA peak is observed at 6 eV, which is likely associated with a core excited resonance, and leads to formation of at least six different negative ion fragment species with the following mass numbers: 16 amu (O~-/NH_2~-), 17 amu (OH~-), 26 amu (CN~-), 28 amu (H_2CN~-), 45 amu (HCO_2~-), 56 amu (H_2C_2NO~-).