Evidence for Conduction Electron-Intramolecular Vibration Interaction in a Platinum Chain Salt

Abstract

Abstract Polarized reflectance measurements on K1.75 Pt(CN)4·1.5H2O, or K(def)CP reveal that there is a deep indentation in the chain-axis reflectance at a substantially lower frequency (1725 cm−1) than the ordinary C [mddot] N stretching frequency (2180 cm-1). The frequency-dependent conductivity, found by Kramers-Kronig analysis of the reflectance, has a deep antiresonance at about the same frequency. This structure is attributed to a phase-phonon mode of the coupled electron-intramolecular vibration system. These data provide the first direct evidence for the importance of the interaction of the conduction electrons with molecular vibrations in a metal chain compound. The dimensionless electron phonon coupling constant is estimated to be Λ ~ 0.28, a result which suggests that this interaction might be important for stabilizing the Peierls distortion in K(def)CP and that it might influence the dc conductivity of the material. In summary, we have found the first direct evidence for the coupling of intramolecular vibrations to the conduction electrons in an inorganic Pt chain salt. This coupling has important consequences for the Peierls transition in K(def)CP as well as for the optical and transport properties.