Browsing by Author "Parthasarathy, Ramapriya"

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    Decay energetics and lifetime measurements of transient negative ions using Rydberg atoms
    (1997) Parthasarathy, Ramapriya; Dunning, F. B.
    Dissociative electron attachment to CFCl$\sb3$, CF$\sb2$Br$\sb2$, and 1,1,1- and 1,1,2-C$\sb2$Cl$\sb3$F$\sb3$ is studied by measuring the velocity and angular distributions of negative ions produced through electron transfer in collisions with velocity selected K(np) Rydberg atoms. Data analysis is done with the aid of Monte Carlo simulations. Measurements indicate that the mean lifetimes of the transient ions CFCl$\sb3\sp{-*}$ and CF$\sb2$Br$\sb2\sp{-*}$ are $\sim$3.5 ps and $\sim$4.5 ps respectively and that only a small fraction of the excess energy of reaction appears in translation. The 1,1,1-C$\sb2$Cl$\sb3$F$\sb3$ data show one reaction channel resulting in immediate dissociation with an ion lifetime of $\sim$0 ps, and a second channel associated with a longer lived intermediate, $\tau\ \sim$ 0.1 to 1.0 ps. Only limited energy transfer occurs for the 1,1,2 isomer but the operative reaction channel(s) could not be identified. Possible reaction mechanisms are discussed with the aid of ab-initio calculations.
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    Use of Rydberg atoms as a microscale laboratory to probe low-energy electron-molecule interactions
    (2001) Parthasarathy, Ramapriya; Dunning, F. B.
    Dissociative and non-dissociative electron attachment processes are investigated via electron transfer in collisions between velocity selected Rydberg atoms and molecules. Low-energy dissociative electron attachment to BrCN and CBrCl 3, over the temperature range 300 to 450K, is examined, by measuring the velocity and angular distributions of negative ions produced. Measurements for BrCN indicate that electron capture leads to the formation of transient BrCN-* ions that dissociate with a mean lifetime tau ∼20 ps to form CN- product ions. No significant Br - production was observed over the present temperature range. Electron transfer to CBrCl3 leads to the formation of both Cl - and Br- ions. The branching ratio of the reaction pathways dramatically changes with temperature. Investigation of non-dissociative electron attachment to C6H6 indicates that benzene anions are formed with lifetimes of ∼3 ps. Influence of a strong applied electric field on background processes like blackbody photoionization and collisional photo ionization, which complicate studies of Rydberg atom collision processes, is analyzed and the results presented.