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Abstract
In this paper, we employ a diabatic model Hamiltonian based on the DIM (diatomics-in-molecules) and DIIS (diatomics-in-ionic-systems) methods to describe the valence and ion-pair states of the iodine molecule, with the objective of characterizing the influence of Ar and Kr rare gas matrices on the ion-pair states. In particular, we combined this model Hamiltonian with classical simulations to calculate the shifts of the ion-pair state emission spectra due to solvation environment. The computed main emission peaks in Ar and Kr solids appear at 378 and 417nm, in excellent agreement with the experimental emission peaks of 380 and 418nm recently observed by Chergui et al. with the identical transition assignments. Our study also shows that these calculated bands correspond to redshifts from the gas phase of 2600 and 5100 cm−1, compared with shifts of 2900 and 4700 cm−1, respectively, observed in experiments, and the equilibrium bond lengths of the D′ (2g) state in Ar and Kr extend to 3.70 and 3.75Å compared to the gas-phase value of 3.594Å, consistent with experimental implications. Emission bands originating from the δ(2u) state are also computed, as well as the counterparts of these bands in the visible region and the results are shown to be in reasonable agreement with experiments. We present a detailed study of the ion-pair state symmetry breaking which mixes the symmetrical gas-phase states resulting in charge localization, and the establishment of permanent molecular dipole moments in these solvated ion-pair state molecules due to local distortion of the polarizable matrix. Finally we use our calculations to explore model defect solvation sites in solid Ar which have been proposed as the source of various ambiguous emission bands in experimental spectra.
Notes
Submitted to appear as part of the special issue of Molecular Physics honouring Professor Ruth Lynden-Bell on her retirement.
We are indebted to the referee for this suggestion.