title: Vibrational anharmonicity and vibrational Stark effect of sulfate ions trapped in potassium, rubidium and cesium chromate.
abstract: Room and low temperature (approximately 100 K) FT-IR and Raman spectra of the sulfate doped K2CrO4, Rb2CrO4 and Cs2CrO4 were recorded. The positions of the nu1, nu3, and nu4 fundamental mode components of the dopant anions were measured. Nine (out of possible ten) second-order stretch-stretch vibrational transitions of the dopant anions were detected. On the basis of these data, the anharmonicity constants and the corresponding harmonic eigenvalues were calculated for several vibrational transitions using second-order perturbation theory expressions. The anharmonicity of the studied second-order transitions of the type nu1 + nu3i increases in the order (SO4/K2CrO4) < (SO4/Rb2CrO4) < (SO4/Cs2CrO4), while for those of the type nu3j + nu3i it basically follows the trend: (SO4/K2CrO4) > (SO4/Rb2CrO4) < (SO4/Cs2CrO4). The measured relative Stark splittings of the nu3 and nu4 mode components of the dopant SO4(2-) anions, as well as the average X13i/3i3j values decrease in the order (SO4/K2CrO4) > (SO4/Rb2CrO4) > (SO4/Cs2CrO4). In all cases, the splitting is larger for nu3 than for nu4 modes, indicating a smaller angular than the bond length distortion. The theory of vibrational Stark effect suggests that the observed frequency shifts of the nu1, nu3 and nu4 mode components may be attributed to the increase of the field strength at the doped anion site going from K2CrO4 to Cs2CrO4. The Stark splitting of these modes, on the other hand, implies that the internal crystalline field vector is almost parallel to the (hypothetical) C2 axis of the slightly distorted dopant tetrahedral anions.
authors.affiliation: Institute of Chemistry, Faculty of Natural Sciences and Mathematics, St Cyril and Methodius University, Skopje, Macedonia. ljupcop@iunona.pmf.ukim.edu.mk
authors.forename: L
authors.initials: L
authors.lastname: Pejov
authors.forename: V M
authors.initials: VM
authors.lastname: Petrusevski
mesh_terms: D000838:Anions; D002586:Cesium / Q000737:chemistry; D002840:Chromates / Q000737:chemistry*; D007477:Ions; D017680:Potassium Compounds / Q000737:chemistry*; D012413:Rubidium / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013059:Spectrum Analysis, Raman; D013431:Sulfates / Q000737:chemistry*
chemical_list: D000838:Anions; D002840:Chromates; D007477:Ions; D017680:Potassium Compounds; D013431:Sulfates; D002586:Cesium; C027373:potassium chromate(VI); D012413:Rubidium