Electron-phonon coupling and vibrational properties of size-selected linear carbon chains by resonance Raman scattering

Abstract

UV resonance Raman spectroscopy of size-selected linear sp-carbon chains unveils vibrational overtones and combinations up to the fifth order. Thanks to the tunability of the synchrotron source, we excited each H-terminated polyyne (HC_nH with n = 8,10,12) to the maxima of its vibronic absorption spectrum allowing us to precisely determine the electronic and vibrational structure of the ground and excited states for the main observed vibrational mode. Selected transitions are shown to enhance specific overtone orders in the Raman spectrum in a specific way that can be explained by a simple analytical model based on Albrecht’s theory of resonance Raman scattering. The determined Huang–Rhys factors indicate a strong and size-dependent electron-phonon coupling increasing with the sp-carbon chain length.

H-capped polyynes are the simplest system to observe finite-length effects in carbyne. Here, the authors exploit synchrotron-based UV resonance Raman spectroscopy to explain a peculiar intensity behavior of multiple phonons scattering and show a size-dependent electron-phonon coupling.