Dissociation of Molecular Negative Ions of Tetracyanoquinodimethane at the Ionization-Chamber Surface upon Resonance Electron Capture

Resumo

The mass spectrum of negative ions due to resonance electron capture by molecules of tetracyanoquinodimethane (TCNQ), a well-known electron acceptor, has been recorded in order to identify the dissociation processes of TCNQ molecular negative ions on the surface of an ionization chamber at thermal energies of electrons to be attached to the molecules. It has been found that the TCNQ molecular negative ions, preliminarily generated in the gas phase at several resonance maxima, reach the ionization chamber walls owing to a long extra-electron autodetachment lifetime ranging from 25 s in the first resonance at zero electron energy to 0.2 s in the resonance at 3.3 eV and dissociate at the walls as a result of the influence of the surface on the energy balance of the dissociation process. It has been taken into account that without the surface effect on the energy balance, this dissociation would be impossible because of an insufficient energy of the electron captured by the molecule. By B3LYP/6-311G calculations, the most probable dissociation pathways have been determined for negative fragment ions with various empirical formulas. The data obtained can be used to solve problems related to the properties of the TCNQ molecule in interaction with the conductive surface of a metal substrate in electronic devices.