Final Report Summary - MIND (Investigation of electron induced chemical control using momentum imaging of negative ions from dissociative electron attachment)
The development of the ion momentum imaging experiment for dissociative electron attachment (DEA) studies was completed during the first year. Its performance was also characterized using DEA on O2. These have been summarized in the report of the 1st year. During the 2nd year, this apparatus was put to use to conduct experiments on several molecules, which are summarized below:
Electron attachment to CO
DEA to CO has been found to give O─ as the dominant ion with a very weak signal from C─. The O─ cross section peaks at an incident electron energy of 9.6 eV with a sharp onset but tailing off more gradually at higher energies. The velocity slice images of O─ show two dissociation channels with the neutral carbon atom in its ground state (3P) and the first excited state (1D) respectively. The angular distributions of these are found to strongly favour the ejection of O─ in the backward direction.
Measurements on H2 and D2
Despite the importance of H2 and its isotopologues in fundamental science and various applications, no reliable data exist for their dissociative electron attachment (DEA) cross sections. Two measurements almost half a century old, show considerable disparity between them. The reasons for the difference, originally thought as due to secondary electrons, have recently been attributed to the contribution due to UV light and atoms and excited molecules formed at electron energies above 10 eV. We used the new momentum imaging spectrometer to obtain for the first time reliable absolute DEA cross sections for H2 and D2 without being affected by these problems, while ensuring complete collection of all the ions independent of their initial momenta. The measurements also showed larger isotope effect than observed earlier. In addition, isotope effect was observed for the first time in dipolar dissociation by electron impact.
Measurements CF4, CF3Cl, CF3Br, CF3I
In the context of studying electron induced chemistry of molecules relevant to nanolithography we undertook measurements on CF4 and its other halogen derivatives using the momentum imaging spectrometer. These measurements have produced a large wealth of data which are being analyzed.
Electron attachment to CO
DEA to CO has been found to give O─ as the dominant ion with a very weak signal from C─. The O─ cross section peaks at an incident electron energy of 9.6 eV with a sharp onset but tailing off more gradually at higher energies. The velocity slice images of O─ show two dissociation channels with the neutral carbon atom in its ground state (3P) and the first excited state (1D) respectively. The angular distributions of these are found to strongly favour the ejection of O─ in the backward direction.
Measurements on H2 and D2
Despite the importance of H2 and its isotopologues in fundamental science and various applications, no reliable data exist for their dissociative electron attachment (DEA) cross sections. Two measurements almost half a century old, show considerable disparity between them. The reasons for the difference, originally thought as due to secondary electrons, have recently been attributed to the contribution due to UV light and atoms and excited molecules formed at electron energies above 10 eV. We used the new momentum imaging spectrometer to obtain for the first time reliable absolute DEA cross sections for H2 and D2 without being affected by these problems, while ensuring complete collection of all the ions independent of their initial momenta. The measurements also showed larger isotope effect than observed earlier. In addition, isotope effect was observed for the first time in dipolar dissociation by electron impact.
Measurements CF4, CF3Cl, CF3Br, CF3I
In the context of studying electron induced chemistry of molecules relevant to nanolithography we undertook measurements on CF4 and its other halogen derivatives using the momentum imaging spectrometer. These measurements have produced a large wealth of data which are being analyzed.