Resonance Raman spectra of inorganic salt vapors I. Palladium (II) and Copper(II) chloroaluminates

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Abstract
Resonance Raman spectra of vapor molecules formed by reacting gaseous aluminum chloride with solid PdCl2 and CuCl2 have been measured in the temperature range from 500 to 900 K and at total pressures up to 30 atm. The main features of the Raman spectra of the Pd–Al–Cl gaseous molecule are three polarized bands at 298, 176, and 84.5 cm−1. The excitation profiles of these bands exhibit minima in the vicinity of the maximum Pd(II) ligand field absorption, thus suggesting the presence of a center of symmetry in the molecule. A D2h molecular symmetry is proposed for the PdAl2Cl8 vapor complex having Pd(II) as a central atom in square planar coordination. The Raman spectra of the Cu–Al–Cl vapors are interpreted to account for two different molecular species. Three polarized bands at 281, 174.5, and 84.5 cm−1 are assigned to preresonance enhanced A1 fundamentals of the CuAl2Cl8 molecule. Two strong bands at 448 and 291.5 cm−1 and their combinations and ovetones are assigned to resonance enhanced A1 fundamentals of the CuAlCl5 molecule having the Cu(II) in a trigonal coordination. Raman band intensity measurements using different laser line intensities suggest an increasing spectroscopic temperature and decomposition of the complex: CuAl2Cl8(g) →CuAlCl5(g)+AlCl3(g).