Narrow line shape of CaF2 Ca K alpha x-ray fluorescence spectrum due to avoided crossing.

Abstract

It has been found that in the x-ray fluorescence spectra for ${\mathrm{CaF}}_{2}$ the full width at half maximum (FWHM) of the Ca K${\ensuremath{\alpha}}_{1}$ structure is significantly narrower than that in other calcium compounds, and also that the CaSi Ca K${\ensuremath{\alpha}}_{1}$ is accompanied by a strong satellite K\ensuremath{\alpha}''. This K\ensuremath{\alpha}'' satellite has been assigned to a ${\mathrm{KM}}^{2}$\ensuremath{\rightarrow}${\mathrm{LM}}^{2}$ transition, in which the spectator holes originate from the shakeoff of M electrons during the photoionization of a 1s electron. Other satellites within the natural width of the K${\ensuremath{\alpha}}_{1}$ structure were also found, using numerical deconvolution of the measured spectra. The origin of the chemical effect on the FWHM modification is interpreted using cluster molecular-orbital calculations of (${\mathrm{CaF}}_{8}$${)}^{6\mathrm{\ensuremath{-}}}$ for both ground and 1${s}^{\mathrm{\ensuremath{-}}1}$ hole states: The pseudocrossing of atomic orbitals of Ca 3p and F 2s transfers the shakeoff hole from the Ca 3p to F 2s at the creation of a Ca 1${s}^{\mathrm{\ensuremath{-}}1}$ hole; consequently, the satellite of ${\mathrm{CaF}}_{2}$ is weakened.