Raman spectra and lattice vibrations in single crystals of potassium acid phthalate

Raman scattering from single crystals of potassium acid phthalate has been observed with the 4880 Å and 5145 Å excitations of an argon ion laser. The room temperature Raman spectra, recorded with a Jarrel‐Ash spectrometer, in the region 0–300 cm−1, exhibit broad bands which are attributed to the translatory and rotatory types of lattice vibrations of the potassium and acid phthalate ions in the crystal. Experiments were carried out at 77 K using a Spex double monochromator and the Raman scattering in the second‐order of the gratings were observed. The result was a splitting of the several broad bands into their components. Assignments of these low frequency Raman spectra, consistent with the crystal structure and the group theoretical predictions is given. Variations in intensities of some of the spectra due to crystal orientation are also observed and briefly discussed.