Absolute DEA cross section measurement of a chiral molecule

Shaw, Kushal Kumar (2019) Absolute DEA cross section measurement of a chiral molecule. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Chiral molecules are of great interests to scientists in order to understand the origin of the universe, and also to understand the dynamics of low energy electron impact on complex organic molecules. Our molecule of interest, propylene oxide has recently been discovered in space. Analysis of the contents of the Murchison meterorite shows preference of one enantiomer over another. We are mainly interested in studying low energy electron-molecule collision. These collisions gives rise to a temporary negative Ion state (TNI state) which arises from the parent molecule, This negative ion resonant state then decays into one neutral fragment and one anionic fragment via dissociative electron attachment (DEA). Ion pair formation is also observed, which occurs via Ion Pair dissociation (IPD). We have measured the absolute DEA cross section for the chiral molecule propylene oxide with a time of ight mass spectrometer using the Relative ow technique. and observed a resonant peak around 6.5 eV. From the mass spectrum, we understand that this peak arises due to the formation of CH₃⁻ . Increase of the incident electron energy results in ion-pair formations and thus we see a large increase in the number of counts of the fragment negative ions beyond 8 eV incident electron energy. We also inferred that the TNI state was lying below the Ion pair state in the morse potential curve. Our primary aim is to understand the behaviour of these R and S isomers of propylene oxide on collision with spin polarized electrons. However, we use an unpolarized electron gun. The total cross section of the racemic mixture propylene oxide is actually the sum of the DEA cross sections of R and S-propylene oxide.

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