Electron DDCS for ionization of O$_{2}$ under gast C$^{6+}$ ion impact and interference oscillation

S. NANDI; A. N. AGNIHOTRI; C. A. TACHINO; R. D. RIVAROLA; F. MARTÍN; L. C. TRIBEDI

Heidelberg

Conferencia; XVI International Conference on the Physics of Highly Charged Particles; 2012

The DDCS studies of low energy electrons emitted in ionization of medium-Z atoms and molecules by different projectiles are reported in a few cases [1]. But such studies are relatively scarce for multi-electron systems, except for a few experimental work based on N$_{2}$ and O$_{2}$ [2] and the theoretical calculations on N$_{2}$ ionization by fast proton impact [3]. In the present work, we have measured the absolute double differential cross sections (DDCS) for electron emission in ionization of oxygen molecules under the impact of 42 and 51 MeV bare carbon ions. In addition we are interested to observe aby oscillations in the electron spectrum due to the interference. The experimental chamber consists of a high vacuum chamber which includes a motorized turntable and an electrostatic hemispherical analyser. The electrons of energy starting from a few eV to 600 eV emitted in an angular range of 30º to 150º were detected. The DDCS spectra have been compared with the continuum distorted wave-eikonal initial state (CDW-EIS) calculations. A simple molecular representation for the triplet initial molecular state was used for the theoretical calculations. Contributions from different alpha and beta orbitals are considered, according to the corresponding electron spin character. Double differential cross sections are calculated, in the CDW-EIS model, by integrating the post-form of the scattering matrix element, over the transverse momentum transfer and averaging over the molecular solid angle. The results on the DDCS and SDCS are in qualitative agreement with the prediction of the model used. Also, the DDCS radio of (O$_{2}$/2 O) derived by dividing the experimental DDCS for molecular oxygen with the theoretical DDCS for atomic oxygen, does not show prominent oscillatory behaviour arising from the Young-type interference, unlike that has been observed in the case of H$_{2}$ [4]. Similarly, the forward-backward angular asymmetry parameter, as deduced from DDCS values at 30º and 150º increases monotonically with increase in the velocity of the emitted electrons and does not show any oscillation due to the double slit interference. The apparent absence of the oscillation in the spectra can be qualitatively explained in terms of cancellation of contributions arising from different molecular orbitals [5].[1] Suarez et al., Phys. Rev. A 48, 4339 (1993).[2] Baran et al., Phys. Rev. A 78, 012710 (2008).[3] Winkworth et al., NIMB 267, 373 (2009); Tachino et al. J. Phys. B 45, 25201 (2011).[4] Misra et al., Phys. Rev. Lett. 92, 153201 (2004).[5] Nandi et al., Phys. Rev. A (in press).