Murray H. Brooker

Raman spectroscopic studies of aqueous uranyl nitrate and perchlorate systems

Abstract Raman spectra have been obtained for the hydrate melts UO 2 (NO 3 ) 2 ·6H 2 O and UO 2 (ClO 4 ) 2 ·7H 2 O and for aqueous solutions of these salts over a wide range of solution composition. There was no evidence of ion-pair formation with uranyl perchlorate but uranyl nitrate formed a weak complex UO 2 NO 3 + with β 1 = 0.15 ± 0.04 at ionic strength 6.25. Complex formation was strongly enhanced by increased ionic strength. Raman depolarization measurements indicated both monodentate and bidentate linkage of nitrate to uranyl. Remarkably large changes in the molar scattering efficiencies of the nitrate modes accompanied the complex formation and suggested that there was considerable electron redistribution in the UO 2 NO 3 + complex.

Observation of the oxidation of galena using Raman spectroscopy

Abstract Oxidation of galena (PbS) to oxysulfates, (PbO·PbSO4, 3PbO·PbSO4 and 4PbO·PbSO4), has been observed using Raman spectroscopy. Peaks associated with the oxidation products have been assigned. The reaction appears to be a high temperature oxidation induced by the high laser (∼25 mW at 514.5 nm) power density at freshly cleaved galena surfaces. Damage to the galena surface was observed visually under the microscope. Moderate laser powers (∼5 mW at 514.5 nm) did not result in any damage. No Raman bands were observed or expected for freshly cleaved galena because it has the rock salt structure. Laser-induced production of these oxysulfates is dramatically different from high temperature methods previously employed. This procedure will permit easy identification of galena in complex mineral ore samples. Spontaneous air oxidation of freshly cleaved galena to oxides or polysulfides was not detected.

Raman spectroscopic investigations of structural aspects of the different phases of lithium sodium and potassium nitrate

Abstract Raman spectra have been obtained for LiNO 3 , NaNO 3 and KNO 3 as oriented single crystals and polycrystalline solids over a wide range of temperatures up to the melting points. The anomalous component previously observed in the symmetric stretching region and attributed to a disordered nitrate group has been studied as a function of temperature. The results suggest that the peak may have a hot band origin such that transitions 0001 → 1001 and 0100→ 1100 may occur in addition to the ground state transition, 0000→ 1000 of nitrate. In the symmetric stretching region the shift of the hot band is sufficiently large to ensure that the modes of this origin are not coupled to the ground state lattice in the usual way. Hot bands with an external mode origin could not be detected. KNO 3 (II), KNO 3 (III), NaNO 3 (II) and LiNO 3 , have ordered structures with small amounts of disorder of a hot band origin. KNO 3 (I) and NaNO 3 (I) have similarly disordered structures but exhibit minor differences due to different relative populations and symmetries of the disordered sites. Raman studies of the disordered phases suggest that the crystal symmetry is lower than the “average” structure deduced from X-ray diffraction methods. A number of bands previously reported have not been detected while several bands were reassigned on the basis of 15 N substitution.

Raman spectroscopic investigation of aqueous FeSO4 in neutral and acidic solutions from 25‡C to 303‡C: inner- and outer-sphere complexes

Raman spectra of aqueous FeSO4 and (NH4)2SO4 solutions have been recorded over broad concentration and temperature ranges. Whereas the v1-SO42- band profile is symmetrical in noncomplexing (NH4)2SO4 solutions, in FeSO4 solutions a shoulder appears on the high-frequency side, which increases in intensity with increasing concentration and temperature. The molar scattering coefficient of the v1-SO42- band is the same for all forms of sulfate in (NH4)2SO4 and FeSO4 solutions and is independent of temperature up to 150‡C, the highest temperature studied. The high-frequency shoulder is attributed to the formation of a contact ion pair, Fe2+OSO3/2-, as is the splitting of the v3-SO42- antisymmetric stretching mode which is observed in the FeSO4 solution. The bending modes v2-SO42- and v4-SO42-, normally forbidden in the isotropic spectrum, show a gain in intensity with increasing ion-pair formation. A polarized band has been assigned to the Fe2+-O ligand vibration. No higher associates or anionic complexes are required to interpret the spectroscopic data. No evidence of contact ion pairing between Fe2+ and HSO44- could be detected at temperatures up to 303‡C in 1 molal solutions of FeSO4 with an excess of 2 molal H2SO4.

Raman Spectroscopy of Aqueous ZnSO4 Solutions under Hydrothermal Conditions: Solubility, Hydrolysis, and Sulfate Ion Pairing

Raman spectra have been measured for aqueous ZnSO4 solutions under hydrothermal conditions at steam saturation to 244°C; solubility has been recorded as a function of temperature from 25 to 256°C. The high-temperature Raman spectra contained two polarized bands, which suggest that a second sulfato complex, possibly bidentate, is formed in solution, in addition to the 1:1 zinc(II) sulfato complex, which is the only ion pair identified at lower temperatures. Under hydrothermal conditions, it was possible to observe the hydrolysis of the zinc(II) aquo ion by measuring the relative intensity of bands due to SO42− and HSO4− according to the equilibrium reaction Zn(OH2)6]2+ + SO42−⇌[Zn(OH2)5OH]+ + HSO4− The precipitate in equilibrium with the solution at 210°C could be characterized as ZnSO4 · H2O (gunningite) by x-ray diffraction (XRD) and Raman and infrared spectroscopy. At 244°C the equilibrium precipitate could be identified as ZnSO4 (zincosite).

On the Nature of Fluoride Ion Hydration

Hydration of aqueous fluoride ions has been studied by theoretical ab initiocalculations in an attempt to understand the experimental Raman spectrum.Calculations for hydrated fluoride, F− (H2O)n where n = 1–10, have been performedat the RHF/6-31 + G* level. A relatively stable geometry exists for n = 6; abovethis number, additional waters hydrogen bond to water of the hydrated fluoride.On the long time scale of the ab initio calculation or experimental diffractionstudies, the average coordination of fluoride is 6. However, it has been possibleto interpret the low-frequency Raman spectrum on the basis of a singlehydrogen-bonded water molecule, F− ... HOH. To rationalize these results, it is proposedthat the average coordination of fluoride is 6, but on the time scale of the Ramanexperiment the fluoride is symmetrically bonded to only one hydrogen of onewater molecule.

Raman and infrared studies of lithium and cesium carbonates

Abstract Raman spectra have been obtained for solid lithium and cesium carbonate over a wide range of temperatures. The results are consistent with the crystal structures, C2/c for lithium carbonate, and P21/c for cesium carbonate. No phase transitions were detected for the solids over the temperature range from 77 K to the melting points. The difference in the crystal structures results in significantly different correlation-field-splitting effects in the out-of-plane bending mode, ν2 of the carbonate ion. The stacking of the planar carbonate ions in lithium carbonate results in very large correlation field splitting in the ν2 and 2ν2 regions. An anomalously small shift of the peak position of the ν2 band of 12CO2−3 relative to the main band of 12CO2−3 for Li2CO3 has also been explained. The 13CO2−3 ion in natural abundance can be treated as a partially decoupled guest impurity in the lattice of the strongly coupled 12CO2−3 host.

Raman studies of hydration of hydroxy complexes and the effect on standard partial molar heat capacities

Abstract Raman spectroscopic studies of aqueous hydroxy complexes B(OH) 3 , B(OH) 4 2− , Al(OH) 4 − , Zn(OH) 4 2− , and their deuterated analogues provide compelling evidence for the presence of strong hydrogen bonding of water in the outer solvation sphere to the oxygen of the hydroxy ligand in the first coordination sphere. The deuterated complexes are more strongly hydrogen bonded than the hydrogen complexes. The fact that these hydrogen-bonding effects for the hydroxy borates are much more pronounced than for the aluminate and zincate anions can account for the unexpectedly large differences in the standard partial molar heat capacities of B(OH) 4 − and A1(OH) 4 − . The extension of semi-empirical solvation models based on the Born approximation for aqueous hydrolyzed species will need to consider the rather large and specific effect of hydrogen bonding of water to the hydroxide ion.

Raman studies of the phase transition in KClO3

Abstract Raman measurements of KClO 3 from 77 to 630 K have confirmed the presence of a single phase transition at about 545 K. The transition was monitored by following the temperature dependence of the frequency and intensity of two external lattice modes of A g character at about 50 and 80cm −1 . The differences in other regions of the vibrational spectra of the two phases were very small and indicated that the transition involved only a minor structural rearrangement of the ClO 3 − ion. The results are consistent with the centrosymmetric space group Pcmm ( D 2 h 16 ) suggested by Ramachandran and Lonappan ( Acta crystallogr . 10 , 281, 1957). There was no evidence for anion disorder in the high temperature phase. The measured heat of transition was only about 25 J mol −1 l.

Raman and infrared spectral studies of anhydrous potassium and rubidium carbonate

Abstract Raman and infrared spectra of anhydrous K 2 CO 3 and Rb 2 CO 3 were measured at 300 and at 80 K. Infrared transmission, multiple internal reflection and polarized specular reflection techniques were used to determine transverse optical (TO) and longitudinal optical (LO) mode frequencies. The observed vibrational spectra for both salts were in excellent agreement with a C 2h unit cell group analysis which suggests that the crystal structures of anhydrous K 2 CO 3 and Rb 2 CO 3 are isomorphous (Spare group: P2 1 /c). Unlike Na 2 CO 3 , the K 2 CO 3 and Rb 2 CO 3 structures are not complicated by disordering of CO 3 = groups over two sets of non-equivalent sites. Studies of the isotopically substituted ions, 13 C 16 O 3 = and 12 C 16 O 2 18 O = , were employed to confirm assignments.