Vibrational Spectra of [Pd(dmit)2] Dimer (dmit = 1,3-dithiole-2-thione-4,5-dithiolate): Methodology for Examining Charge, Inter-Molecular Interactions, and Orbital

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We have developed a methodology for analyzing the lattice, charge, and orbital in two-dimensional molecular conductors comprising dimers of [Pd(dimt)2] ([Pd(dimt)2]2) using C=C stretching vibrational modes. After confirming vibrational modes for non-dimerized and loosely dimerized materials, we provide assignments for the four C=C stretching modes --- two IR-active modes and two Raman-active modes --- for the tight dimer. Of the four modes, the Raman-active and the lowest frequency mode is attributed to redistribution of the molecular orbital due to tight dimerization. By analyzing the vibrational spectra in the charge-ordered (CO) state of Et2Me2Sb[Pd(dmit)2]2, we have found that the four modes are reflect in the intra-dimer interaction, the inter-dimer interaction, molecular charges and orbital levels. The results suggest that the vibrational spectroscopy is a powerful method to investigate electronic correlations, electron--phonon interactions, etc. in [Pd(dimt)2] salts.
2011-07-15