Fourier transform infrared study of perchlorate (35ClO4− and 37ClO4−) anions isomorphously isolated in potassium permanganate matrix. Vibrational anharmonicity and pseudo-symmetry effects Original Research Article

Fourier transform infrared spectra of isotopomeric 35ClO4− and 37ClO4− anions isomorphously isolated in potassium permanganate matrix were recorded at room and low temperature (LT, ∼100 K). On the basis of the detected second-order vibrational transitions involving the dopant species ν3 mode components, anharmonicity constants and harmonic eigenvalues for these modes were calculated. Although the overall appearance of the region of fundamental vibrational transitions in the spectra of dopant perchlorate anions may be better explained in terms of a pseudo-symmetry (the so-called ‘latent’ symmetry) site group C2v, corresponding to the pseudo-symmetry space group Imma, instead of the (rigorous) crystallographic Cs one (corresponding to the crystallographic Pnma space group), an opposite statement seems to be valid for the region of the second-order vibrational transitions. The vibrational mode mixing (a ‘Fermi-like’ resonance) of the ClO4− ν1 mode with the ν3a site group component is almost negligible.