Phase-transition induced changes in the electron–phonon coupling of all-trans-β-carotene

Abstract

The resonance Raman spectra of the fundamental, combination, and second harmonic modes around the CC and CC stretches of all-trans-β-carotene in 1,2-dichloroethane solution are obtained in the 323–83K temperature range. The Raman scattering cross-section of the fundamentals in the liquid and solid phases generally increases as the temperature decreases, except for the liquid–solid phase transition, which exhibits a decreasing trend. The relative Raman intensities of the combination and harmonic modes of the CC bonds increase as the temperature decreases. The Raman bandwidths of the CC bonds gradually become narrow but then appear a turning-point in the phase transition. The temperature-induced fundamental modes are analyzed using a coherent weakly damped electron–lattice vibration model and resonant Raman effects. The changes in the combination and harmonic modes are interpreted using the aforementioned model as well as the theory of electron–phonon interaction.