Optical Absorption of CdI2 Single Molecule and Clusters Incorporated into Zeolite Na-FAU

概要

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The absorption spectra of CdI2 molecules adsorbed through a vapor phase into zeolite Na-FAU are investigated at liquid nitrogen temperature by changing the loading density $L_{\text{d}}$ of CdI2 per supercage from a dilute condition of 0.1 to a saturated condition of 5.5. The theoretical absorption spectrum of a CdI2 molecule is also derived using the wave functions obtained from a relativistic self-consistent-field discrete-variational X$\alpha$ calculation. A predominant band is observed at 5.8 eV together with sub-bands at 5.0 and 5.5 eV at $L_{\text{d}} = 0.1$. The comparison between the experimental and theoretical spectra clarifies that these bands originate from the electronic transitions of an isolated CdI2 molecule. Moreover, it suggests that the CdI2 molecule interacts with zeolite. Another three bands appear at 4.8, 5.3, and 6.0 eV at $L_{\text{d}} = 2.0$ when $L_{\text{d}}$ increases, which are attributed to a CdI2 two-molecule cluster. The lowest absorption band continuously shifts toward the lower-energy side with an increase in $L_{\text{d}}$ between 2.0 and 5.5. This shift is explained by the quantum size effect on photoexcitation energy.
2009-10-15