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E. Krishnakumar

Publications and source records attributed to E. Krishnakumar.

8 recordsLinked to original sources
arXiv2026

Endcap-Type Paul Trap for Precision Spectroscopy and Studies of Controlled Interactions

We present the design and fabrication of an endcap-type Paul trap. The trap is designed for studies with Ca$^{+}$ and Yb$^{+}$. The design, fabrication process, and characterization are presented in detail with a focus on trapping a single compensated ion at the rf node. A custom-built imaging system of $NA = 0.14$ and magnification $\approx 22 \times$ performs close to diffraction-limit and resolves multi-ion clusters. Controlled ion loading and characterization of the trap are performed using $^{40}$Ca$^{+}$. The experimentally determined quadrupole coefficient of the trap is $\approx 0.3$, which is very close to the design value. The relative frequency shift along the spectroscopy beam due to excess micromotion (EMM) is at the level of $3.5\times 10^{-18}$ for $^{40}$Ca$^{+}$. Applications of this trap encompass single-ion-based optical frequency standards, tests of fundamental physics, the study of mesoscopic Coulomb clusters, and the controlled interaction of a single ion with co-trapped atoms.

physics.atom-ph↗
arXiv2024

Quantum coherence in dissociative electron attachment: isotope effect

Dissociative electron attachment (DEA) is one of the processes that shows a strong coupling between the nuclear and electronic degrees of freedom in a molecule. This coupling results in an efficient transformation of the kinetic energy of attaching free electrons into the chemical energy of the compound molecule. A recent discovery of quantum coherence in this process has opened a whole new dimension in its description. On the other hand, the mass variation in isotopes of the constituent atoms has a profound effect on DEA. In quantum coherence observed in DEA, the isotope effect depicts itself in terms of change in the phase and the amplitude of the interfering dissociation paths. Here, we report the quantum coherence observed in DEA to HD, an isotopologue of H$_2$. In this isotopologue, both H$^-$ and D$^-$ show identical forward-backward asymmetry in the angular distribution. We explain these findings using the interference between two quantum paths, with the permanent dipole moment of the asymmetric mass playing no role in the process.

physics.chem-ph↗
arXiv2017

QDB: a new database of plasma chemistries and reactions

One of the most challenging and recurring problems when modelling plasmas is the lack of data on key atomic and molecular reactions that drive plasma processes. Even when there are data for some reactions, complete and validated datasets of chemistries are rarely available. This hinders research on plasma processes and curbs development of industrial applications. The QDB project aims to address this problem by providing a platform for provision, exchange, and validation of chemistry datasets. A new data model developed for QDB is presented. QDB collates published data on both electron scattering and heavy-particle reactions. These data are formed into reaction sets, which are then validated against experimental data where possible. This process produces both complete chemistry sets and identifies key reactions that are currently unreported in the literature. Gaps in the datasets can be filled using established theoretical methods. Initial validated chemistry sets for SF$_6$/CF$_4$/O$_2$ and SF$_6$/CF$_4$/N$_2$/H$_2$ are presented as examples.

physics.plasm-ph↗
arXiv2010

Dissociative Electron Attachment to Polyatomic Molecules - I : Water

Using the velocity map imaging technique, we studied and characterized the process of Dissociative Electron Attachment (DEA) in polyatomic molecules like Water, Hydrogen Sulphide, Ammonia, Methane, Formic Acid and Propyl Amine. We present the details of these studies in a series of 5 articles. In the first article here, we discuss the DEA process in gas phase water ($H_{2}O$ and $D_{2}O$) molecules. Electrons of 6.5 eV, 8.5 eV and 12 eV are captured by water molecules in neutral ground state to form $H_{2}O^{-*}$ ($D_{2}O^{-*}$) resonant states which dissociate into an anion fragment and one or more neutrals. Kinetic energy and angular distributions of the fragment anions $H^{-}$($D^{-}$) and $O^{-}$ produced from the three negative ion resonant states in the entire $2\pi$ scattering range are obtained. Unique angular distribution patterns are observed at the 8.5 eV and 11.8 eV resonances showing dissociation dynamics beyond the axial recoil approximation.

physics.chem-ph↗
arXiv2010

Dissociative Electron Attachment to Polyatomic Molecules - III : Ammonia

In this paper, we discuss the dissociative electron attachment process in Ammonia. Kinetic energy and angular distributions of H^{-} and NH_{2}^{-} fragment anions across the two well known resonances at 5.5 eV and 10.5 eV are reported. The angular distributions show deviation of axial recoil approximation akin to that observed in water.

physics.chem-ph↗
arXiv2010

Dissociative Electron Attachment to Polyatomic Molecules - IV : Methane

In this paper, we discuss the dissociative electron attachment process in Methane. Kinetic energy and angular distributions of H^{-} and CH_{2}^{-} fragment anions across the broad resonance about 10 eV is reported. Angular distribution of H^{-} ions changes from being perpendicular to forward-backward scattering across the resonance. Possibility of Jahn-Teller effect on excitation of the triply degenerate 1t2 molecular orbital is inferred.

physics.chem-ph↗
arXiv2010

Dissociative Electron Attachment to Polyatomic Molecules - V : Formic Acid and Propyl Amine

In this paper, we discuss the dissociative electron attachment process in Formic Acid and Propyl Amine. These are molecules containing more than one functional group and have low symmetry (Cs group). We measured the kinetic energy and angular distributions of fragment H^{-} ions from the resonances observed in these molecules and compared with that in the precursor molecules, namely - Water, Ammonia and Methane. Measurements suggest that the dissociation dynamics in bigger molecules are independent of overall symmetry of the molecule, rather depend only on the local symmetry of functional group and bond orientation factors.

physics.chem-ph↗