The 4d-4f dipole resonance of the Pr atom in an endohedral metallofullerene, Pr@C82

The photoion yield spectra of an endohedral metallofullerene Pr@C-82 were measured in the photon energy range of 100-150eV by using time-of-flight mass spectrometry. Parent ions Pr@C-82(+), Pr@C-82(2+) and Pr@C-82(3+) were observed in t he mass spectra. The photoion yield spectra of Pr@C-82(2+) showed a broad peak at 120-140eV that was assigned to the 4d-4f giant dipole resonance of the encapsulated Pr atoms. Absolute photoabsorption cross sections of Pr@C-82 were evaluated from the photoion yield spectra to be 37 +/- 12 Mb at 110eV (off-resonance) and 52 +/- 13 Mb at 130eV (on-resonance). These cross sections of Pr@C-82 were compared with the results of Ce@C-82, the only metallofullerene whose photoionization properties have ever been studied near the 4d edge of the encapsulated metal atom. The enhancement of photoabsorption due to the giant resonance was found to be similar in Pr@C-82 and Ce@C-82, but there are marked differences in the peak shapes, which can be explained as due to interference effects between the fullerene cage and the encapsulated metal atoms. (c) 2007 Elsevier Ltd. All rights reserved.