Chapter 8 Infrared and Raman Spectroscopy of Temperature‐Responsive Polymers
Yasushi Maeda
Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, University of Fukui, Fukui, 910‐8507, Japan
8.1 Introduction
Infrared (IR) absorptions and Raman scatterings are based on molecular vibrations, which are sensitive to chemical structures, conformations, and interactions of molecules. IR absorptions take place in the resonant conditions with the molecular vibrations. The energy of light with frequency of ν is given by hν, where h is Planck's constant. If the energy of light exactly matches the energy separation (ΔE) between two different vibrational energy levels of a molecule, the light can be absorbed to excite it from the lower level to the higher one (Figure 8.1). Because the molecule usually exists in the vibrational ground state at around room temperature, the major absorption is due to the excitation from the ground state to the first excited energy level with frequency of ν vib, which is named the fundamental transition. Therefore, it is simply said that the energy of IR photon can be absorbed by the molecule, if ν = ν vib and the selection rule is fulfilled. The IR region of the electromagnetic wave is conveniently divided into three regions: the near‐, mid‐, and far‐IR, named for their relation to the visible light. The mid‐IR (∼4000–400 cm−1) corresponds to the excitation energy for the fundamental molecular vibrations. The higher energy ...