Laboratoire Francis PERRIN
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Dissociative Electron Attachment probed by Velocity Map Imaging Séminaires SPAM LFP
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30/04/2009 à 11:00
LIDYL Bât 522, p 138 CEA-Saclay
Dhananjay NANDI
Velocity map imaging (VMI) is recent, a high resolution variant of the ion imaging technique. The technique has been successfully applied to photo-ionization, photo-dissociation and photo-detachment studies [1]. We have shown for the first time that the VMI is a powerful technique to study the differential cross section in the entire angular range with unprecedented sensitivity for the dissociative electron attachment (DEA) process[2,3]. It simultaneously provides both kinetic energy and angular distribution measurements far more accurately. The performance of the spectrometer has been evaluated using DEA to oxygen (O2) and found to be exceptionally good [2]. The measurements also provided for the first time evidence for the presence of the 4u resonance in DEA to O2 [4]. We probe this unique capability of the technique to resolve the existing controversy on the DEA to nitric oxide (NO). Our angular distribution data show finite cross sections in the forward direction and strong forward-backward asymmetry and is explained due to the interference between different partial waves involved in the process. Based on the experimental results and the theoretical calculations, we propose that the observation of N (4S) atoms in an earlier experiment employing high magnetic field may be due to ‘magnetically allowed predissociation’. This could impact chemical control using electrons [5].

[1] Imaging in Molecular Dynamics, Ed. by B. Whitaker, Cambridge University Press, Cambridge (2003).
[2] D. Nandi, V. S. Prabhudesai, E. Krishnakumar, and A. Chatterjee, Rev. Sci. Instrum. 76, 053107 (2005).
[3] D. Nandi, V. S. Prabhudesai, and E. Krishnakumar, Rad. Phys. Chem. 75, 2151 (2006).
[4] V. S. Prabhudesai, D. Nandi, and E. Krishnakumar, J. Phys. B 39, L277 (2006).
[5] D. Nandi, V. S. Prabhudesai, B. Nestman, and E. Krishnakumar, Phys. Rev. Lett. (Submitted).