Wavelength‐selective resonance Raman spectroscopy of a finite polyene: Solid‐state all‐trans‐β‐carotene

Publisher Website
Google Scholar
Abstract
Two samples of solid all‐trans‐β‐carotene which differed in their degrees of crystallinity were studied using visible absorption and resonance Raman spectroscopy.The absorption spectrum of a commercial crystalline β‐carotene sample revealed two bands at 18 450 and 20 040 cm−1 which were not present in the absorption spectrum of a prepared amorphous sample. Instead, the spectrum of the amorphous material showed a band at 19 268 cm−1 which is in a position approximately half way between the 18 450 and 20 040 cm−1 bands. From these observations these two latter bands are assigned to the Davydov components of the crystalline β‐carotene.The resonance Raman spectrum of crystalline all‐trans‐β‐carotene revealed several frequencies for the backbone CC stretching mode, νcc, as the laser excitation wavelength was varied. This frequency was observed to vary between 1516 and 1525 cm−1. The amorphous carotene sample also exhibited a wavelength‐dependent Raman spectrum where νcc ranged from 1516 to 1522 cm−1 initially. On further exposure to laser radiation (30–60 min) at 514.5 nm, the range increased to an upper limit of 1525 cm−1, which was attributed to a photochemical product formed in both the crystalline and amorphous samples. The wavelength‐dependent νcc frequency of these carotene samples is interpreted as being due to resonance‐enhanced Raman bands of β‐carotene molecules with different effective double bond chain lengths originating from separate micro‐domains in the solid samples.

This publication has 10 references indexed in Scilit: