Temperature dependence of the Raman bandwidths for the lattice and internal modes in ammonium halides close to the lambda-phase transitions

We study here the temperature dependence of our Raman bandwidths for the upsilon(5) lattice modes of NH(4)Cl (T(lambda)=241 K) and NH(4)Br (T(lambda)=235 K) and for the upsilon(2) internal mode of NH(4)Cl close to the lambda-phase transitions. Our Raman bandwidths of those modes are studied using a power-law formula on the basis of the soft mode-hard mode coupled model. From our analysis, we extract the values of the critical exponent beta for the order parameter of the ferro-ordered (NH(4)Cl) and the antiferro-ordered (NH(4)Br) phases. Our beta values are close to zero which exhibits a logarithmic behaviour in the vicinity of the lambda-phase transitions in NH(4)Cl and NH(4)Br. It is indicated here that the ammonium halides (NH(4)Cl and NH(4)Br) undergo a weakly first order or nearly second order phase transition close to the lambda transition point.     

Temperature dependence of the damping constant and the order parameter close to the lambda phase transitions in ammonium halides

This study gives our calculation for the damping constant, using the expressions derived for an Ising pseudospin-phonon coupled system in the ammonium halides (NH(4)Cl and NH(4)Br). For this calculation of the damping constant, we use the temperature dependence of the order parameter calculated from the molecular field theory. We predict here the damping constants for the v(5) (174 cm(-1)) and v(5) (177 cm(-1)) Raman modes of NH(4)Cl and NH(4)Br, respectively, below T(lambda) and compare them with our observed bandwidths measured as a function of temperature for those phonon modes at zero pressure. Our predictions agree well with the observed bandwidths below T(lambda) for those modes in both ammonium halide structures, in particular for NH(4)Br. Some discrepancy that occurs below T(lambda) for the v(5) (174 cm(-1)) mode of NH(4)Cl, is explained in terms of the model studied here.     

Raman frequency shifts of an internal mode near the tricritical and second order phase transitions in NH4Cl

This study gives our analysis for the frequency shifts of the v2 (1708 cm-1) Raman mode in NH4Cl close to its tricritical (P=1.6 kbar) and second order (P=2.8 kbar) phase transitions. From our analysis, we extract the values of the critical exponent which describes the critical behavior of the Raman frequency shifts for this internal mode for the pressure conditions studied in NH4Cl. Our exponent value of alpha approximately 0.2 for the tricritical phase transition is close to the values of 1/16 (TTc) for the specific heat, predicted from a 3D Ising model. Our exponent values for the second order phase transition (P=2.8 kbar) for TTc are comparable with those reported in earlier studies.     

Analysis of the Raman intensities near the phase transitions in ammonium halides

This study concentrates on the temperature dependence of the Raman intensities for the lattice modes in ammonium halides (NH(4)Cl and NH(4)Br) close to phase transitions. We predict their intensities using the results of a shell model for the Raman polarizability within the framework of an Ising pseudospin-phonon coupled model. From our observed Raman intensities of those phonon modes studied here, we extract the values of the critical exponent for the order parameter in these crystalline systems. The exponent values indicate that the Raman intensities show a logarithmic divergence at higher pressures in NH(4)Cl, whereas they predict a lambda-type phase transition at zero pressure in NH(4)Br.     

Infrared spectrum of NH4+(H2O): evidence for mode specific fragmentation

The gas phase infrared spectrum (3250-3810 cm-1) of the singly hydrated ammonium ion, NH4+(H2O), has been recorded by action spectroscopy of mass selected and isolated ions. The four bands obtained are assigned to N-H stretching modes and to O-H stretching modes. The N-H stretching modes observed are blueshifted with respect to the corresponding modes of the free NH4+ ion, whereas a redshift is observed with respect to the modes of the free NH3 molecule. The O-H stretching modes observed are redshifted when compared to the free H2O molecule. The asymmetric stretching modes give rise to rotationally resolved perpendicular transitions. The K-type equidistant rotational spacings of 11.1(2) cm-1 (NH4+) and 29(3) cm-1 (H2O) deviate systematically from the corresponding values of the free molecules, a fact which is rationalized in terms of a symmetric top analysis. The relative band intensities recorded compare favorably with predictions of high level ab initio calculations, except on the nu3(H2O) band for which the observed value is about 20 times weaker than the calculated one. The nu3(H2O)/nu1(H2O) intensity ratios from other published action spectra in other cationic complexes vary such that the nu3(H2O) intensities become smaller the stronger the complexes are bound. The recorded ratios vary, in particular, among the data collected from action spectra that were recorded with and without rare gas tagging. The calculated anharmonic coupling constants in NH4+(H2O) further suggest that the coupling of the nu3(H2O) and nu1(H2O) modes to other cluster modes indeed varies by orders of magnitude. These findings together render a picture of a mode specific fragmentation dynamic that modulates band intensities in action spectra with respect to absorption spectra. Additional high level electronic structure calculations at the coupled-cluster singles and doubles with a perturbative treatment of triple excitations [CCSD(T)] level of theory with large basis sets allow for the determination of an accurate binding energy and enthalpy of the NH4+(H2O) cluster. The authors' extrapolated values at the CCSD(T) complete basis set limit are De [NH4+-(H2O)]=-85.40(+/-0.24) kJ/mol and DeltaH(298 K) [NH4+-(H2O)]=-78.3(+/-0.3) kJ/mol (CC2), in which double standard deviations are indicated in parentheses.     

A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals, including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm-1 region and in the 950-1000 cm-1 region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. For example, soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm-1 (UO2)2+ (nu1), 909.6 and 898.0 cm-1 (UO2)2+ (nu3), 268.2, 257.8 and 246.9 cm-1 are assigned to the nu2 (delta) (UO2)2+. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm-1 are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm-1 region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm-1 and in the 390-420 cm-1 region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 cm-1 and 3600-3700 cm-1.     

Pippard relations applied to the lambda-phase transition in NH4Br

We establish here a linear variation of the specific heat C(P) with the frequency shifts (1/nu)( partial differentialnu/ partial differentialT)(P) close to the lambda-phase transition in NH(4)Br (T(lambda)=234K). This linear relationship is based on our spectroscopically modified Pippard relations. For this verification of our relations, we use our observed Raman frequencies of the lattice mode of nu(7) (56cm(-1)) and the internal mode of nu(2) (1684cm(-1)) in the NH(4)Br crystalline system. Our study given here indicates that the thermodynamic data can be obtained from the measured frequencies.     

Infrared and polarized Raman spectra of (CH3)2NH2Al(SO4)2 x 6H2O

FTIR and single crystal Raman spectra of (CH3)2NH2Al(SO4)2 x 6H2O have been recorded at 300 and 90 K and analysed. The shifting of nu1 mode to higher wavenumber and its appearance in Bg species contributing to the alpha(xz) and alpha(yz) polarizability tensor components indicate the distortion of SO4 tetrahedra. The presence of nu1 and nu2 modes in the IR spectrum and the lifting of degeneracies of nu2, nu3, and nu4 modes are attributed to the lowering of the symmetry of the SO4(2-) ion. Coincidence of the IR and Raman bands for different modes suggest that DMA+ ion is orientationally disordered. One of the H atoms of the NH2 group of the DMA+ ion forms moderate hydrogen bonds with the SO4(2-) anion. Al(H2O)6(3+) ion is also distorted in the crystal. The shifting of the stretching modes to lower wavenumbers and the bending mode to higher wavenumber suggest that H2O molecules form strong hydrogen bonds with SO4(2-) anion. The intensity enhancement and the narrowing of nu1SO4, deltaC2N and Al(H2O)6(3+) modes at 90 K confirm the settling down of the protons in the hydrogen bonds formed with H2O molecules and NH2 groups. This may be one of the reasons for the phase transition observed in the crystal.     

Electronic and vibrational spectra of Mn rich sursassite

The optical spectrum of Mn2+ in octahedral coordination for sursassite is characterized by well resolved bands at 580, 515, 470, 390, 340, and 295 nm (17240, 19420, 21280, 25640, 29410 and 33900 cm-1). Crystal field parameters evaluated from the observed bands are Dq=690, B=680 and C=2800 cm-1. A broad band centred around 13000 cm-1 attributed to Fe(III) ion is an impurity in sursassite confirmed from EDX analysis. Vibrational spectra have been investigated both by IR and Raman spectroscopy. The correlation between vibrational modes and the structural properties of the manganese silicate, sursassite, is made and compared with other silicates. Two vibrational modes of CO(3)2- observed; the antisymmetric stretching mode (nu3) at 1420 cm-1 (IR active) and the out-of-plane bending mode (nu2) (IR and Raman active) at approximately 875 cm-1. This confirms the Mn rich phases in sursassite as observed from SEM probably an Mn carbonate-rhodochrosite.     

Raman spectrum of [Ru(CNBu t)(CO)(eta2-C6H4-2-CHO)(PPh3)2][BF4].2CDCl3 shows that the crystallographically determined bifurcated hydrogen-bonding interaction Cl3CD...F2BF2- is an example of a blue-shifting hydrogen bond

Raman data suggest that a crystallographically determined Cl3CD...F2BF2- interaction in the solid-state structure of [Ru(CNBut)(CO)(eta2-C6H4-2-CHO)(PPh3)2][BF4].2CDCl3 is an example of a blue-shifting bifurcated hydrogen bond. The nu(C-D) band blue-shifts 5 cm-1 to 2269 cm-1 compared to 2264 cm-1 for CDCl3 in the gas phase and 20 cm-1 from frozen CDCl3 at 2249 cm-1. A conventional interpretation of these band shifts would suggest that the CCl2 fragment of DCCl3 is a stronger hydrogen-bond acceptor than the BF2 fragment of a BF4- group.     

Energy funneling of IR photons captured by dendritic antennae and acceptor mode specificity: anti-stokes resonance raman studies on iron(III) porphyrin complexes with a poly(aryl ether) dendrimer framework

A series of poly(aryl ether) dendrimer chloroiron(III) porphyrin complexes (LnTPP)Fe(III)Cl (number of aryl layers [n]=3 to 5) were synthesized, and their Boltzmann temperatures under IR irradiation were evaluated from ratios of Stokes to anti-Stokes intensities of resonance Raman bands. While the Boltzmann temperature of neat solvent was unaltered by IR irradiation (LnTPP)Fe(III)Cl (n=3 to 5), all showed a temperature rise that was larger than that of the solvent and greater as the dendrimer framework was larger. Among vibrational modes of the metalloporphyrin core, the temperature rise of an axial Fe-Cl stretching mode at 355 cm-1 was larger than that for a porphyrin in-plane mode at 390 cm-1. Although most of the IR energy is captured by the phenyl nu8 mode at 1597 cm-1 of the dendrimer framework, an anti-Stokes Raman band of the phenyl nu8 mode was not detected, suggesting the extremely fast vibrational relaxation of the phenyl mode. From these observations, it is proposed that the energy of IR photons captured by the aryl dendrimer framework is transferred to the axial Fe-Cl bond of the iron porphyrin core and then relaxed to the porphyrin macrocycle.     

Vibrational spectroscopy of selected minerals of the rosasite group

Minerals in the rosasite group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite have been studied by a combination of infrared and Raman spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the molecular structure is similar to malachite. A comparison is made with the spectrum of malachite. The rosasite mineral group is characterised by two OH stretching vibrations at approximately 3401 and 3311 cm-1. Two intense bands observed at approximately 1096 and 1046 cm-1 are assigned to nu1(CO3)2- symmetric stretching vibration and the delta OH deformation mode. Multiple bands are found in the 800-900 and 650-750 cm-1 regions attributed to the nu2 and nu4 bending modes confirming the symmetry reduction of the carbonate anion in the rosasite mineral group as C2v or Cs. A band at approximately 560 cm-1 is assigned to a CuO stretching mode.     

Internal rotation in NH4(+)-Rg dimers (Rg = He, Ne, Ar): potential energy surfaces and IR spectra of the nu 3 band

The intermolecular potential energy surfaces for the electronic ground states of the ammonium ion-rare gas dimers NH4(+)-He and NH4(+)-Ne are calculated at the MP2 and CCSD(T)/aug-cc-pVXZ (X = D/T/Q) levels of theory. The global minima of both potentials correspond to proton (vertex)-bound structures, Re = 3.13 A, De = 171 cm-1 (He) and Re = 3.21 A, De = 302 cm-1 (Ne). The face- and edge-bound structures are local minima and transition states for the internal rotation dynamics, corresponding to barriers of approximately 20 (He) and 50 cm-1 (Ne). The ab initio potentials are employed in numerical solutions to the rotation-intermolecular vibration Hamiltonian to determine the term values and the rotational and distortion constants for the lowest bound levels in the intramolecular ground vibrational state of both complexes. The results are used to assess the accuracy of two-dimensional (fixed-R) representations of the potentials for determining the internal rotor levels in the ground and nu 3 vibrational states. This model is employed to produce simulations of the IR nu 3 transitions, which are compared to the experimental spectra recorded using photofragmentation spectroscopy. In the case of NH4(+)-Ne the potential parameters are least-squares fitted to the experimental spectrum. The trends within the NH4(+)-Rg series (Rg = He, Ne, Ar) revealed by both the IR spectra and theoretical calculations are discussed.     

A Raman spectroscopic study of the uranyl phosphate mineral bergenite

Raman spectroscopy at 298 and 77 K of bergenite has been used to characterise this uranyl phosphate mineral. Bands at 995, 971 and 961 cm-1 (298 K) and 1006, 996, 971, 960 and 948 cm-1 (77K) are assigned to the nu1(PO4)3- symmetric stretching vibration. Three bands at 1059, 1107 and 1152 cm-1 (298 K) and 1061, 1114 and 1164 cm-1 (77 K) are attributed to the nu3(PO4)3- antisymmetric stretching vibrations. Two bands at 810 and 798 cm-1 (298 K) and 812 and 800 cm-1 (77 K) are attributed to the nu1 symmetric stretching vibration of the (UO2)2+ units. Bands at 860 cm-1 (298 K) and 866 cm-1 (77 K) are assigned to the nu3 antisymmetric stretching vibrations of the (UO2)2+ units. UO bond lengths in uranyls, calculated using the wavenumbers of the nu1 and nu3(UO2)2+ vibrations with empirical relations by Bartlett and Cooney, are in agreement with the X-ray single crystal structure data. Bands at (444, 432, 408 cm-1) (298 K), and (446, 434, 410 and 393 cm-1) (77 K) are assigned to the split doubly degenerate nu2(PO4)3- in-plane bending vibrations. The band at 547 cm-1 (298 K) and 549 cm-1 (77 K) are attributed to the nu4(PO4)3- out-of-plane bending vibrations. Raman bands at 3607, 3459, 3295 and 2944 cm-1 are attributed to water stretching vibrations and enable the calculation of hydrogen bond distances of >3.2, 2.847, 2.740 and 2.637 A. These bands prove the presence of structurally nonequivalent hydrogen bonded water molecules in the structure of bergenite.     

Investigation of nu(N-H) and nu(C-N) stretching modes of propylamine (C3H7NH2) in a binary system C3H7NH2 + CH3OH via concentration dependent Raman study and ab initio calculations

Raman spectra of propylamine (C3H7NH2) and its binary mixtures, C3H7NH2 + CH3OH with varying mole fractions of the reference system, C3H7NH2, C were recorded in two widely apart wavenumber regions, 3100-3600 cm(-1) and 1225-1325 cm(-1). In the former region, the two Raman bands at approximately 3305 and approximately 3326 cm(-1), obtained after the line shape analysis, which were assigned to symmetric nu(N-H) and anti-symmetric nu(N-H) stretching modes, respectively, show a downshift upon dilution. However, whereas the nu(N-H) anti-symmetric mode shows a shift of 18.6 cm(-1), the nu(N-H) symmetric mode shows a much smaller shift (5.7 cm(-1)) between neat liquid and high dilution, C = 0.1. This aspect has been explained using the optimized geometries calculated employing ab initio theory (MP2 level) for the neat C3H7NH2 and its different hydrogen-bonded complexes. The linewidth versus concentration plot for the nu(N-H) anti-symmetric stretching mode, however exhibits a distinct maxima at C = 0.4, which has been explained as a slight departure from the concentration fluctuation model. In the latter region, a symmetric peak is observed, which corresponds to nu(C-N) stretching mode, which shows an upshift upon dilution and an almost linear concentration dependence. This has also been explained in terms of the parameters obtained from the optimized geometries of the different hydrogen-bonded complexes.     

Raman study of the hexafluoroaluminate ion in solid and molten FLINAK

Raman spectra have been obtained for matrix-isolated AlF6(3-) in an LiF/NaF/KF (FLINAK) eutectic mixture. Three Raman bands characteristic of the hexafluoroaluminate ion were identified in the solids formed from FLINAK melts which contained small amounts (5-11 mol%) of either AlF3 or Na3AlF6. The three allowed Raman-active bands of the matrix-isolated octahedral complex ion, nu 1(A1g), nu 2(Eg), and nu 5(F2g), were observed at 560.5, 380, and 325 cm-1, respectively, for the solid sample at 25 degrees C. Wavenumbers and relative intensities were similar to those of Na3AlF6 (cryolite), K3AlF6, and K2NaAlF6 (elpasolite) and other crystals known to contain discrete, octahedral AlF6(3-) ions. Peak positions, half-widths, and relative intensities for the bands were measured for samples at temperatures different from room temperature through the melting transition and into the molten state. The transition from high-temperature solid to molten salt at about 455 degrees C occurred gradually without perceptible change in the peak positions, half-widths, or relative intensities. For a sample in molten FLINAK at 455 degrees C, the nu 1(A1g), nu 2(Eg), and nu 5(F2g) modes of the AlF6(3-) ion were observed at 542, 365, and 324 cm-1, respectively. Raman depolarization experiments were consistent with these assignments, and the low value of the depolarization ratio of the nu 1(A1g) mode at 542 cm-1 indicated that the sample was molten above 455 degrees C. Differential thermal analysis also indicated that the FLINAK samples melted at about 455 degrees C. Raman measurements were performed for samples at temperatures from 25 to 600 degrees C in a silver dish, on a hot stage, in an argon-filled atmosphere, under a microscope. Additional Raman experiments were performed on samples at temperatures from 25 to 750 degrees C in a conventional graphite windowless cell, in an argon-filled quartz tube, in a standard furnace. Over the concentration range 4.8-11 mol% AlF3 (CR 23-8.0) in FLINAK, only bands due to the AlF6(3-) ion were detected. There was no evidence to support the presence of other aluminum complexes in these melts.     

A Raman spectroscopic study of synthetic giniite

The mineral giniite has been synthesised and characterised by XRD, SEM and Raman and infrared spectroscopy. SEM images of the olive-green giniite display a very unusual image of pseudo-spheres with roughened surfaces of around 1-10microm in size. The face to face contact of the spheres suggests that the spheres are colloidal and carry a surface charge. Raman spectroscopy proves the (PO4)3- units are reduced in symmetry and in all probability more than one type of phosphate unit is found in the structure. Raman bands at 77K are observed at 3380 and 3186cm-1 with an additional sharp band at 3100cm-1. The first two bands are assigned to water stretching vibrations and the latter to an OH stretching band. Intense Raman bands observed at 396, 346 and 234cm-1are attributed to the FeO stretching vibrations. The giniite phosphate units are characterised by two Raman bands at 1023 and 948cm-1 assigned to symmetric stretching mode of the (PO4)3- units. A complex band is observed at 460.5cm-1 with additional components at 486.8 and 445.7cm-1 attributed to the nu(2) bending modes suggesting a reduction of symmetry of the (PO4)3- units.     

Raman spectroscopic study of the tellurite minerals: rajite and denningite

Tellurites may be subdivided according to formula and structure. There are five groups based upon the formulae (a) A(XO3), (b) A(XO3).xH2O, (c) A2(XO3)3.xH2O, (d) A2(X2O5) and (e) A(X3O8). Raman spectroscopy has been used to study rajite and denningite, examples of group (d). Minerals of the tellurite group are porous zeolite-like materials. Raman bands for rajite observed at 740, and 676 and 667 cm(-1) are attributed to the nu1 (Te2O5)(2-) symmetric stretching mode and the nu3 (TeO3)(2-) antisymmetric stretching modes, respectively. A second rajite mineral sample provided a more complex Raman spectrum with Raman bands at 754 and 731 cm(-1) assigned to the nu1 (Te2O5)(2-) symmetric stretching modes and two bands at 652 and 603 cm(-1) are accounted for by the nu3 (Te2O5)(2-) antisymmetric stretching mode. The Raman spectrum of dennigite displays an intense band at 734 cm(-1) attributed to the nu1 (Te2O5)(2-) symmetric stretching mode with a second Raman band at 674 cm(-1) assigned to the nu3 (Te2O5)(2-) antisymmetric stretching mode. Raman bands for rajite, observed at (346, 370) and 438 cm(-1) are assigned to the (Te2O5)(2-)nu2 (A1) bending mode and nu4 (E) bending modes.     

Electronic and resonance Raman spectra of [Au2(CS3)2]2-. Spectroscopic properties of a "short" Au(I)-Au(I) bond

The anion [Au2(CS3)2]2- has an unusually short Au-Au distance (2.80 A) for a binuclear Au(I) complex. We report detailed Raman studies of the nBu4N+ salt of this complex, including FT-Raman of the solid and UV/vis resonance Raman of dimethyl sulfoxide solutions. All five totally symmetric vibrations of the anion have been located and assigned. A band at delta nu = 125 cm-1 is assigned to nu (Au2). The visible-region electronic absorption bands (384 (epsilon 30,680) and 472 nm (epsilon 610 M-1 cm-1)) are attributable to CS3(2-) localized transitions, as confirmed by the dominance of nu sym(C-Sexo) (delta nu = 951 cm-1) in RR spectra measured in this region. An absorption band at 314 nm (22,250 M-1 cm-1) is assigned as the metal-metal 1(d sigma*-->p sigma) transition, largely because nu sym(C-Sexo) is not strongly enhanced in RR involving this band. Observation of the expected strong resonance enhancement of nu (Au2) was precluded as a result of masking by intense solvent Rayleigh scattering in the UV.     

Raman-spectral depolarisation ratios of ions in concentrated aqueous solution. The next-to-negligible effect of highly asymmetric ion surroundings on the symmetry properties of polarisability changes during vibrations of symmetric ions. Ammonium sulphate and tetramethylammonium bromide

Depolarisation ratios rho have been measured for the Raman spectra of solutions of composition (NH4)2 SO4*11H2O and (CH3)4NBr*29D2O. Even though the former's vibration spectrum shows clear evidence of lowered ion symmetries (presence of nu1 of SO4(2-) in the IR spectrum, IR versus R nu(max) shifts for nu3 and nu4 of SO4(2-) and nu4 of NH4+) nu1 of SO4(2-) has (apparent) rho of only 0.014, while nu2, nu3 and nu4 of SO4(2-) and nu4 (probably also nu2) of NH4+ have rho in the range 0.73-0.77; within the experimental error and base line uncertainty the latter are equal to 0.75, i.e. to rho(max) with the geometry of the optics used. For (CH3)4NBr symmetric N+-C stretching has rho 0.012; all-in-phase C-H stretching and four overtones in Fermi resonance with it have rho in the range 0.02-0.035, but the deviation from zero here is in part due to underlying or overlapping depolarised bands. The sufficiently well isolated antisymmetric CH stretching and degenerate CH bending bands again have rho in the range 0.74-0.76. These results show that the selection rules in respect of rho, which apply strictly only to isolated molecules, are for practical purposes still valid for molecules in strongly symmetry-distorting external environments in the liquid phase. More specifically: (A) During vibrations in which quasi-spherical intramolecular symmetry is retained, the externally caused aspherical component of the polarizability ellipsoid does not change aspherically to a sufficient extent for an appreciably intense anisotropic Raman band to appear. (B) During intramolecularly anti-symmetric vibrations of symmetric molecules, the portion of the externally caused distortion of the polarizability ellipsoid that fails to cancel over a whole vibration period is not large enough to give rise to an appreciably intense isotropic component of the Raman band. This means in practice rho for these Raman bands is still rho(max), even for concentrated aqueous solutions.