Observation of a “new” quadrupole transition at 7.7 eV in CF3Cl by momentum-transfer-resolved electron energy loss spectroscopy
✍ Scribed by J.F. Ying; C.P. Mathers; K.T. Leung; H.P. Pritchard; C. Winstead; V. McKoy
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 838 KB
- Volume
- 212
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
A "new" non-dipole electronic transition at 7.7 eV in CF,CI 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 *E +'A, (LUMOtHOMO) 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-d 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 'A, ground-state potential energy curve accesses the repulsive region of the 'E excited-state curve, suggesting that this quadrupole transition may lead to dissociation of the C-Cl bond