An experimental and theoretical study of the valence shell photoelectron spectrum of tetrafluoromethane

Abstract

The complete valence shell photoelectron spectrum of tetrafluoromethane has been recorded using synchrotron radiation and the observed structure has been interpreted using ionisation energies and relative spectral intensities computed using the third-order algebraic-diagrammatic-construction (ADC(3)) scheme for the one-particle Green's function and the outer valence Green's function (OVGF) method. The ADC(3) calculations were performed using both the original variant based on the Dyson equation and the recently proposed non-Dyson scheme. The theoretical predictions for the single-hole ionic states due to outer valence shell ionisation agree satisfactorily with the experimental results. Ionisation from the inner valence 2t(2) and 3a(1) orbitals is strongly influenced by reorganisation effects and the intensity is spread amongst numerous satellites. Highly resolved spectra have been measured for the (CT2)-T-2 and the (D) over tilde (2)A(1) states, and the vibrational structure has been associated primarily with excitation of the v(1)(+) (a(1)) mode. However, the analyses also provide evidence for excitation of the Jahn-Teller active v(2)(+) (e) mode in the (C) over tilde T-2(2) state, and the v(3)(+) (t(2)) mode the (D) over tilde (2)A(1) state. Excitation of this latter mode can be explained in terms of vibronic coupling between the (C) over tilde T-2(2) and the (D) over tilde (2)A(1) states. Photoelectron angular distributions and branching ratios have been determined and demonstrate that shape resonances affect the outer valence shell photoionisation dynamics. The experimental results are compared with previous theoretical predictions but a consistent interpretation has not been obtained. The major difficulty concerns the uncertainty in the locations of valence shell transitions into the 5a(1) and the 5t(2) virtual orbitals. (C) 2004 Elsevier B.V. All rights reserved.