MP2 and CCSD(T) ab initio calculations have been carried out to elucidate geometrical structure and vibrational frequencies of representative lanthanide trihalides LnX3 (Ln = La, Lu; X = F, Cl) explicitly including temperature, anharmonic, inert-gas matrix, and spin−orbit effects. The results have been compared with gas-phase electron diffraction, gas-phase IR measurements, and IR spectra of molecules trapped in inert-gas matrices. On the Born−Oppenheimer surface LaCl3, LuF3, and LuCl3 adopt trigonal planar (D3h) geometry while LaF3 assumes a slightly pyramidal (C3v) structure. Because of normal-mode anharmonicities, the resulting thermal average bond angles are considerably lower than the equilibrium ones, while vibrationally averaged bond lengths are predicted to be longer. The inert-gas matrix effects, modeled by the coordination of two inert-gas molecules LnX3·IG2 (IG = Ne, Ar, Xe, and N2), are substantial and strongly depend on the polarizability of coordinating particles. Coordinating inert-gas units always favor the tendency of LnX3 molecules to adopt planar structure and induce noticeable frequency shifts.

Anharmonic, Temperature, and Matrix Effects on the Molecular Structure and Vibrational Frequencies of Lanthanide Trihalides LnX3 (Ln = La, Lu; X = F, Cl).

MINICHINO, Camilla
2005

Abstract

MP2 and CCSD(T) ab initio calculations have been carried out to elucidate geometrical structure and vibrational frequencies of representative lanthanide trihalides LnX3 (Ln = La, Lu; X = F, Cl) explicitly including temperature, anharmonic, inert-gas matrix, and spin−orbit effects. The results have been compared with gas-phase electron diffraction, gas-phase IR measurements, and IR spectra of molecules trapped in inert-gas matrices. On the Born−Oppenheimer surface LaCl3, LuF3, and LuCl3 adopt trigonal planar (D3h) geometry while LaF3 assumes a slightly pyramidal (C3v) structure. Because of normal-mode anharmonicities, the resulting thermal average bond angles are considerably lower than the equilibrium ones, while vibrationally averaged bond lengths are predicted to be longer. The inert-gas matrix effects, modeled by the coordination of two inert-gas molecules LnX3·IG2 (IG = Ne, Ar, Xe, and N2), are substantial and strongly depend on the polarizability of coordinating particles. Coordinating inert-gas units always favor the tendency of LnX3 molecules to adopt planar structure and induce noticeable frequency shifts.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11563/2513
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