Effect of Background Signal on Momentum Imaging

The velocity Slice Imaging technique has revolutionised electron molecule interaction studies. Multiple electrostatic lens assemblies are often used in spectrometers for resolving low kinetic energy fragments. However, in a crossed-beam experiment with an effusive molecular beam, the extended source of ion generation due to the presence of the background gas creates artefacts on the momentum images as we try to magnify them beyond a certain size. Here, we present a systematic study of this effect on momentum imaging and the solutions to address this issue by background subtraction with suitable magnification. Additionally, we demonstrated that a supersonic molecular beam target helps minimise these artefacts in the image magnification by reducing the background signal. These systematic findings may bring valuable insight into the investigation of low kinetic energy release processes involving electron impact, ion impact, and merge beam experiments with large interaction volumes where high magnification is needed

Production of electronically excited NO via DEA to NO

Dissociative electron attachment (DEA) to NO2 in the 7–11 eV range is studied using velocity slice imaging technique. Two distinct channels are observed in the DEA corresponding to O– + NO(A 2Σ+) and O– + NO(C 2Π and/or D 2Σ+). While NO(A 2Σ+) is found to be formed only in very high vibrational levels, NO(C 2Π and/or D 2Σ+) is found to be formed with vibrational distribution starting from v = 0. From the angular distribution of the O– ions leading to the NO(C 2Π and/or D 2Σ+) channel, we obtain the symmetry of the negative ion resonance to be dominantly B1 with small contribution from B2

Dynamics of Site Selectivity in Dissociative Electron Attachment in Aromatic Molecules

Dissociative electron attachment has shown site selectivity in aliphatic molecules based on the functional groups present in them. This selectivity arises from the core excited resonances that have excited parent states localized to a specific site of the functional group. Here, we show that such site selectivity is also observed in the amine group when present in aromatic molecules. However, the proximity of the aromatic ring to the functional group under investigation has a substantial effect on the dissociation dynamics. This effect is evident in the momentum distribution of the hydride ions generated from the amine group. Our results unravel the hitherto unknown facets of the site selectivity in aromatic organic molecules

Negative ion resonances in carbon monoxide: Probing dissociative electron attachment in CO by velocity slice imaging

Abstract: Dissociative electron attachment to CO leading to the formation of O− is studied using the velocityslice imaging technique. The angular distributions we obtained for the C(3P) and the C(1D) limits are found to beconsiderably different from a recent set of measurements [Tian et al., Phys. Rev. A88, 012708 (2013); Wang et al., J. Chem. Phys. 143, 066101(2015)] using a similar technique. The analysis of our results indicate incoherentcontributions from states of Σ and Π symmetries to both these dissociation channelsand rules out the need to invoke coherent excitation of several resonances, in contrast towhat has been done in the above publications. We try to correlate these resonances tothose observed in inelastic scattering and transmission experiments. We also confirm thepresence of a third dissociation channel leading to C(1S) limit