Figure 3

Experimental and calculated FIR spectra of MPC. Both of these spectra are vertically offset. (a) Temperature-dependent experimental spectra. The frequency of each peak at 4 K is given in cm⁻¹. Five peaks at 4 K and three peaks at 298 K observed in the frequency range of 250–350 cm⁻¹ are indicated by blue and red arrows, respectively. (b) Calculated spectra with four dielectric constants for a MPC conformation that provides the best-fitting FIR spectra. The frequencies at ε (dielectric constant) = 4.20 are given in cm⁻¹. The full width at half maximum (FWHM) is set to the same value as that of the well-separated sharp peak at 423 cm⁻¹ experimentally observed at 4 K (FWHM = 4.4 cm⁻¹). A magnification of 200–350 cm⁻¹ is shown on the right. Five modes located between 250 and 350 cm⁻¹ are denoted as ν₁–ν₅. Peaks indicated by blue and red arrows correspond to five peaks observed at 4 K and three peaks observed at 298 K, respectively.