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Published September 10, 1993 | public
Journal Article

Observation of a "new" quadrupole transition at 7.7 eV in CF_3Cl by momentum-transfer-resolved electron energy loss spectroscopy

Abstract

A "new" non-dipole electronic transition at 7.7 eV in CF_3Cl has been observed using momentum-transfer-resolved electron energy loss spectroscopy at 2.5 keV impact energy. The generalized oscillator strength (GOS) of this transition has been determined and found to have a shape characteristic of a quadrupole transition with a maximum at ≈1 au of momentum transfer. Using the results from an ab initio GOS calculation and a single-excitation configuration interaction calculation, we show that this transition corresponds to the ^1E ← ^1A_1 (LUMO ← HOMO) transition with a very small computed dipole transition moment. In particular, this transition is related to an electronic transition from a non-bonding Cl 3p orbital (HOMO) to an antibonding p-σ* C-Cl orbital (LUMO). The nature of the orbitals involved in the transition, together with its small calculated dipole transition moment, strongly suggests that this transition is dominated by quadrupole interaction. The calculated potential energy diagram along the C-Cl bond direction also shows that a vertical transition from the ^1A_1 ground-state potential energy curve accesses the repulsive region of the ^1E excited-state curve, suggesting that this quadrupole transition may lead to dissociation of the C-Cl bond.

Additional Information

© 1993 Elsevier. Received 28 June 1993; in final form 9 July 1993. This work was supported by the Natural Sciences and Engineering Research Council of Canada, and in part by the Canadian Network of Centres of Excellence in Molecular and Interfacial Dynamics. Work at Caltech was supported by the US National Science Foundation.

Additional details

Created:
August 20, 2023
Modified:
October 25, 2023