S. V. K. Kumar

Absolute cross sections for dissociative electron attachment to NF3

Abstract Absolute dissociative electron attachment cross sections for the formation of F−, F2−, and NF2− from NF3 have been measured in a crossed beams geometry by using the relative flow technique. Discrimination against ions with high kinetic energy are eliminated by employing a pulsed electron beam, pulsed ion extraction and a segmented time of flight mass spectrometer. The cross sections for the F− formation, which is the dominant channel, is found to be almost a factor of 2 larger than what is reported earlier. This descrepancy is explained in terms of the discrimination against ions of appreciable kinetic energy in earlier measurements.

Excited state dissociative attachment and couplings of electronic states of

Dissociative attachment of electrons to electronically excited produced by optical pumping is studied. An entirely new application of the dissociative attachment process has been demonstrated to unravel couplings between various states of a molecule which has not been possible by optical spectroscopy. Also, identification of a negative-ion resonance state based on initial state selection of the neutral molecule is achieved for the first time without making any angular distribution measurements.

Orthogonal bipolar spherical harmonics measures: Scrutinizing sources of isotropy violation

The two-point correlation function of the cosmic microwave background temperature anisotropies is generally assumed to be statistically isotropic (SI). Deviations from this assumption could be traced to physical or observational artifacts and systematic effects. Measurement of nonvanishing power in the bipolar spherical harmonic spectra is a standard statistical technique to search for isotropy violations. Although this is a neat tool allowing a blind search for SI violations in the cosmic microwave background sky, it is not easy to discern the cause of isotropy violation by using this measure. In this article, we propose a novel technique of constructing orthogonal bipolar spherical harmonic estimators, which can be used to discern between models of isotropy violation.

Dissociative attachment to excited molecules

Cross-sections for dissociative attachment of electrons to electronically excited molecules produced by optical pumping has been studied. Negative ion resonance states could be identified based on initial state selection of the neutral. Couplings between various states of the neutral molecule could be unraveled which has been difficult using high resolution optical spectroscopy.