Unambiguous observation of F-atom core-hole localization in ${\mathrm{CF}}_4$ through body-frame photoelectron angular distributions

A dramatic symmetry breaking in $K$-shell photoionization of the ${\mathrm{CF}}_4$ molecule in which a core-hole vacancy is created in one of four equivalent fluorine atoms is displayed in the molecular frame angular distribution of the photoelectrons. Observing the photoejected electron in coincidence with an ${\mathrm{F}}^{+}$ atomic ion after Auger decay is shown to select the dissociation path where the core hole was localized almost exclusively on that atom. A combination of measurements and ab initio calculations of the photoelectron angular distribution in the frame of the recoiling ${\mathrm{CF}}_3{}^{+}$ and ${\mathrm{F}}^{+}$ atoms elucidates the underlying physics that derives from the Ne-like valence structure of the F($1s^{-1}$) core-excited atom.

Figure 1

Experimental (relative) and theoretical (absolute) RFPADs for polarization parallel to the C-F recoil axis. The experimental RFPADs use data for $\text{KER}>5.5$ eV. Left to right: Ejected electron energies 3, 5, and 12 eV. Upper panels: Experiment. Lower panels: Theory. Dashed lines are for delocalized and solid red lines localized fluorine $1s$ holes, with delocalized results for 3 and 5 eV multiplied by 1/4 and for 12 eV multiplied by 1/5. Labels indicate the theoretical RFPAD cross section at the outer ring of the polar coordinates.

Figure 2

Potential curve for ${\mathrm{CF}}_4{}^{+}$ dissociation from SCF calculation with $1s$ vacancy enforced on dissociating fluorine. Inset: Mulliken populations showing that the dissociating fluorine atom has a population of nine electrons and is therefore neutral while the ${\mathrm{CF}}_3{}^{+}$ fragment has 32 electrons.

Figure 3

Kinetic energy release (KER) for ejected electron energy of 12 eV. Inset: RFPAD for polarization parallel to the C-F recoil axis (horizontal) measured using only data for $\text{KER}<5.5$ eV compared with calculations for the delocalized fluorine $1s$ hole (from Fig. 1, bottom right).

Figure 4

RFPADs for polarization perpendicular to the C-F recoil axis and $\text{KER}>5.5$ eV. Left, 3 eV, and right, 12 eV, ejected electron energy. Rows top to bottom: Experiment, theory for localized F core vacancy, and theory for delocalized F vacancy.