The fundamental lattice vibrations of the trigonal CdCl2 structure have been analyzed group theoretically. All k=0 optical modes are either infrared or Raman active, so a complete vibrational analysis is possible. Results of far-infrared measurements on crystal and powder samples using a Fourier-transform spectrometer together with single-crystal Raman spectra are presented for CdCl2, CdBr2, MnCl2, and CoCl2. Symmetry assignments of the observed frequencies are made on the basis of polarization behavior. Second-order infrared and Raman spectra are also presented; peaks in the two-phonon axial infrared absorption spectra are assigned to allowed fundamental combinations at k=0. The infrared absorption spectra exhibit additional features in the range 200–4000 cm−1 that are ascribed to impurities.
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Symmetry coordinates for the k=0 modes in CdCl2. The cartesian-coordinate subscripts 1, 2, and 3 refer to the two chlorine atoms and the cadmium atom, respectively. The coordinate system was chosen so that the z axis corresponds to the crystal c axis, and the x axis is one of the three twofold axes corresponding to the rotations C2′.
Representation of D3d
Symmetry coordinate
A1g
Q1 = z1−z2
A2u (acoustic)
Q2 = z1+z2+z3
A2u (optic)
Q3 = z1+z2−2z3
Eg
Q4 = x1−x2
Q5 = −(y1−y2)
Eu (acoustic)
Q6 = x1+x2+x3
Q7 = −(y1+y2+y3)
Eu (optic)
Q8 = x1+x2−2x3
Q9 = −(y1+y2−2y3)
Table III
Frequencies (cm−1), linewidths (cm−1), and assignments of first-order Raman and infrared lines observed in CdBr2 CdCl2, MnCl2, and Cocl2 at room temperature.
Symmetry coordinates for the k=0 modes in CdCl2. The cartesian-coordinate subscripts 1, 2, and 3 refer to the two chlorine atoms and the cadmium atom, respectively. The coordinate system was chosen so that the z axis corresponds to the crystal c axis, and the x axis is one of the three twofold axes corresponding to the rotations C2′.
Representation of D3d
Symmetry coordinate
A1g
Q1 = z1−z2
A2u (acoustic)
Q2 = z1+z2+z3
A2u (optic)
Q3 = z1+z2−2z3
Eg
Q4 = x1−x2
Q5 = −(y1−y2)
Eu (acoustic)
Q6 = x1+x2+x3
Q7 = −(y1+y2+y3)
Eu (optic)
Q8 = x1+x2−2x3
Q9 = −(y1+y2−2y3)
Table III
Frequencies (cm−1), linewidths (cm−1), and assignments of first-order Raman and infrared lines observed in CdBr2 CdCl2, MnCl2, and Cocl2 at room temperature.