不同电解质体系水的拉曼谱的研究

通过一系列电解质体系水的拉曼光谱测量，得到了阴、阳离子种类和浓度引起的水伸缩振动和弯曲振动谱带丰富的变化信息，ＣｌＯ４＾－能有效地破坏水分子间的氢键，随着ＣｌＯ４浓度的增加，水分子间的氢键并非逐步被打断，而是氢键被破坏的水分子越来越多，从而使水分子有序度增大，这种氢键破坏方式符合水的混合模型（ＭｉｘｔｕｒｅＭｏｄｅｌ）ＳＯ＾２－４浓度的增对水的Ｒａｍａｎ光谱影响较小，是由于ＳＯ＾２－４与水分了间的     

Drawing out the structural information of the first layer of hydrated ions: ATR-FTIR spectroscopic studies on aqueous NH4NO3, NaNO3, and Mg(NO3)2 solutions

ATR-FTIR technique was used to obtain the difference spectra of aqueous NH4NO3 NaNO3, and Mg(NO3)2 solutions, with NO3- concentrations ranging from 0 to 4.00 mol dm(-3). The water monomers weakly hydrogen bonded with NO3- ions showed a positive peak near at 3565 cm(-1) for both Mg(NO3)2 and NH4NO3 solutions. The positive peak was shift to approximately 3543 cm(-1) for NaNO3 solutions due to the total contributions of the hydrated NO3- (approximately 3565 cm(-1)) and the hydrated Na+ (approximately 3440 cm(-1)). Compared with perchlorate solutions, the positive peak of nitrate solutions has a red shift of about 20 cm(-1) and the peak area is about half of that of perchlorate solutions with the same concentrations, indicating that the hydrogen bonding between NO3- and water monomers is relative stronger than that between ClO4- and water monomers, and NO3- has a strict requirement on the orientation of water molecules when hydrogen bonded with water monomers due to its planar structure. The ab initio calculations were used to understand the splitting of the nu3 band and hydration effect on the infrared activation of the nu1. The absorbance of nu3b, nu1 and nu2 bands, dependent on the type of cations, was observed to departed from Beer low with increasing concentrations, which is considered as the results of the interactions between cations and nitrate ions.     

FTIR spectroscopic investigations of supersaturated NaClO4 aerosols

Supersaturated NaClO4 aerosols have been studied using a Fourier transform infrared (FTIR) spectrometer coupled with an aerosol flow tube (AFT). Compared with previous Raman results, the water O-H stretching envelope in the supersaturated solutions of NaClO4 aerosols was more structured in response to changing RH, revealing at the same time the existence of water monomers weakly hydrogen-bonded with ClO4- at extremely high concentrations. Due to enhanced ion interactions in the supersaturated solutions of NaClO4 aerosols, the formation of contact ion pairs (CIPs) could be observed without component decomposition for the nondegenerate nu1 band of ClO4-, and the degenerate nu3 band of ClO4- was successfully related to the formation of CIPs in NaClO4 solutions. Based on these observations, a new mechanism featured by the attack of ClO4- upon hydrated Na+ for CIPs formation in the supersaturated solutions of NaClO4 aerosols was further proposed. The anhydrous NaClO4, characterized by the upper limit deliquescence relative humidity (DRH) of approximately 43% and the disappearance of the nu1 band of ClO4- in the infrared spectra, was observed to form on the silicon windows at low RHs.     

Magnesium sulfate aerosols studied by FTIR spectroscopy: hygroscopic properties, supersaturated structures, and implications for seawater aerosols

Supersaturated MgSO4 aerosols and dilute MgSO4 solutions were studied by FTIR spectroscopic techniques (i.e., aerosol flow tube (AFT) and attenuated total reflection (ATR)). The hygroscopic properties of MgSO4 aerosols were investigated with results in good agreement with previous measurements by a scanning electrodynamic balance (SEDB). Well-defined spectral evolutions with changing relative humidity (RH) for the v3 band of SO4(2-) and the water O-H stretching envelope could be directly related to the observed hygroscopic properties of MgSO4 aerosols. When the RH decreased from approximately 55 to approximately 40%, the v1 band of SO4(2-) in supersaturated MgSO4 aerosols was observed to transform from a sharp peak at approximately 983 cm(-1) into a wide band at approximately 1005 cm(-1). The sharp peak at approximately 983 cm(-1) was mainly assigned to such associated complexes of Mg2+ and SO4(2-) as double solvent-separated ion pairs (2SIPs), solvent-shared ion pairs (SIPs), and simple contact ion pairs (CIPs) in supersaturated MgSO4 aerosols, while the wide band at approximately 1005 cm(-1) was due to polymeric CIPs chains, probably the main component of gels formed in MgSO4 aerosols at low RHs. Relating to this v1 band transformation, the peak position of the v(3) band was first shown to be a sensitive indicator of CIPs formation, spanning across approximately 40 cm(-1) on the formation of polymeric CIPs chains, which could also be supported by aerosol composition analysis in the form of water-to-solute molar ratios (WSR). In the water O-H stretching envelope, the absorbance intensities at 3371 and 3251 cm(-1) were selected to represent contributions from weak and strong hydrogen bonds, respectively. The absorbance intensity ratio changing with RH of 3371 to 3251 cm(-1) could be related to the previous observations with the v1 and v3 bands of SO4(2-). As a result, the formation of CIPs with various structures in large amounts was supposed to significantly weaken hydrogen bonds in supersaturated MgSO4 aerosols, while 2SIPs and SIPs were not expected to have similar effects even when occurring in abundance. In comparison with MgSO4 aerosols, the peak positions of the v3 band of SO4(2-) in artificial seawater aerosols implied that the MgSO4 component should be contained as gels or concentrated solutions in the fissures of microcrystals of sea salts for freshly formed seawater aerosols at low RHs.     

Raman observation of the interactions between NH4+, SO4(2-), and H2O in supersaturated (NH4)2SO4 droplets

High signal-to-noise ratio (S/N) Raman spectra of (NH(4))(2)SO(4) droplets deposited on a quartz substrate were obtained from dilute to supersaturated states upon decreasing the relative humidity (RH). When the molar water-to-solute ratio (WSR) decreases from 16.8 to 3.2, the v(1)-SO(4)(2-) band changes very little, that is, showing a red-shift of only about 1 cm(-1) (from 979.9 to 978.8 cm(-1)) and an increase of its full width at half-maximum (fwhm) from 8.3 to 9.8 cm(-1). Other vibration modes such as v(2)- and v(4)-SO(4)(2-) bands appear almost constantly at 452 and 615 cm(-1). Such kind of a spectroscopic characteristic is different from previous observation on other cations, indicating that the interactions between SO(4)(2-) and NH(4)+ in supersaturated states are similar to those between SO(4)(2-) and H(2)O in dilute states. After fitting the Raman spectra with Gaussian functions in the spectral range of 2400-4000 cm(-1), we successfully extracted six components at positions of 2878.7, 3032.1, 3115.0, 3248.9, 3468.4, and 3628.8 cm(-1), respectively. The first three components are assigned to the second overtone of NH(4)+ umbrella bending, the combination band of NH(4)+ umbrella bending and rocking vibrations, and the NH(4)+ symmetric stretching vibration, while the latter three components are from the strongly, weakly, and slightly hydrogen-bonded components of water molecules, respectively. With a decrease of the RH, the proportion of the strongly hydrogen-bonded components increases, while that of the weakly hydrogen-bonded components decreases in the droplets. The coexistence of strongly, weakly, and slightly hydrogen-bonded water molecules must hint at a similar hydrogen-bonding network of NH(4)+, SO(4)(2-), and H(2)O to that of pure liquid water in supersaturated (NH(4))(2)SO(4) droplets.     

IR, 1H NMR, mass, XRD and TGA/DTA investigations on the ciprofloxacin/iodine charge-transfer complex

Raman and infrared spectra of two polymorphous minerals with the chemical formula Fe3+(SO4)(OH)·2H2O, monoclinic butlerite and orthorhombic parabutlerite, are studied and the spectra assigned. Observed bands are attributed to the (SO4)2- stretching and bending vibrations, hydrogen bonded water molecules, stretching and bending vibrations of hydroxyl ions, water librational modes, Fe-O and Fe-OH stretching vibrations, Fe-OH bending vibrations and lattice vibrations. The O-H?O hydrogen bond lengths in the structures of both minerals are calculated from the wavenumbers of the stretching vibrations. One symmetrically distinct (SO4)2- unit in the structure of butlerite and two symmetrically distinct (SO4)2- units in the structure of parabutlerite are inferred from the Raman and infrared spectra. This conclusion agrees with the published crystal structures of both mineral phases.     

Air-liquid interfaces of aqueous solutions containing ammonium and sulfate: spectroscopic and molecular dynamics studies

Investigations of the air-liquid interface of aqueous salt solutions containing ammonium (NH(4)(+)) and sulfate (SO(4)(2-)) ions were carried out using molecular dynamics simulations and vibrational sum frequency generation spectroscopy. The molecular dynamics simulations show that the predominant effect of SO(4)(2-) ions, which are strongly repelled from the surface, is to increase the thickness of the interfacial region. The vibrational spectra reported are in the O-H stretching region of liquid water. Isotropic Raman and ATR-FTIR (attenuated total reflection Fourier transform infrared) spectroscopies were used to study the effect of ammonium and sulfate ions on the bulk structure of water, whereas surface sum frequency generation spectroscopy was used to study the effect of these ions on the interfacial structure of water. Analysis of the interfacial and bulk vibrational spectra reveal that aqueous solutions containing SO(4)(2-) perturb the interfacial water structure differently than the bulk and, consistent with the molecular dynamics simulations, reveal an increase in the thickness of the interfacial region.     

Theoretical studies on photoelectron and IR spectral properties of Br2.-(H2O)n clusters

We report vertical detachment energy (VDE) and IR spectra of Br2.-.(H2O)n clusters (n=1-8) based on first principles electronic structure calculations. Cluster structures and IR spectra are calculated at Becke's half-and-half hybrid exchange-correlation functional (BHHLYP) with a triple split valence basis function, 6-311++G(d,p). VDE for the hydrated clusters is calculated based on second order Moller-Plesset perturbation (MP2) theory with the same set of basis function. On full geometry optimization, it is observed that conformers having interwater hydrogen bonding among solvent water molecules are more stable than the structures having double or single hydrogen bonded structures between the anionic solute, Br2.-, and solvent water molecules. Moreover, a conformer having cyclic interwater hydrogen bonded network is predicted to be more stable for each size hydrated cluster. It is also noticed that up to four solvent H2O units can reside around the solute in a cyclic interwater hydrogen bonded network. The excess electron in these hydrated clusters is localized over the solute atoms. Weighted average VDE is calculated for each size (n) cluster based on statistical population of the conformers at 150 K. A linear relationship is obtained for VDE versus (n+3)(-1/3) and bulk VDE of Br2.- aqueous solution is calculated as 10.01 eV at MP2 level of theory. BHHLYP density functional is seen to make a systematic overestimation in VDE values by approximately 0.5 eV compared to MP2 data in all the hydrated clusters. It is observed that hydration increases VDE of bromine dimer anion system by approximately 6.4 eV. Calculated IR spectra show that the formation of Br2.--water clusters induces large shifts from the normal O-H stretching bands of isolated water keeping bending modes rather insensitive. Hydrated clusters, Br2.-.(H2O)n, show characteristic sharp features of O-H stretching bands of water in the small size clusters.     

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.     

Mid-infrared characterization of the NH4 +(H2O)n clusters in the neighborhood of the n=20 "magic" number

Vibrational predissociation spectra are reported for size-selected NH4+ (H2O)n clusters (n=5-22) in the 2500-3900 cm(-1) region. We concentrate on the sharp free OH stretching bands to deduce the local H-bonding configurations of water molecules on the cluster surface. As in the spectra of the protonated water clusters, the free OH bands in NH4+ (H2O)n evolve from a quartet at small sizes (n<7), to a doublet around n=9, and then to a single peak at the n=20 magic number cluster, before the doublet re-emerges at larger sizes. This spectral simplification at the magic number cluster mirrors that found earlier in the H+(H2O)n clusters. We characterize the likely structures at play for the n=19 and 20 clusters with electronic structure calculations. The most stable form of the n=20 cluster is predicted to have a surface-solvated NH4+ ion that lies considerably lower in energy than isomers with the NH4+ in the interior.     

A vibrational spectroscopic study of the mixed anion mineral sanjuanite Al2(PO4)(SO4)(OH)·9H2O

The mineral sanjuanite Al2(PO4)(SO4)(OH)·9H2O has been characterised by Raman spectroscopy complimented by infrared spectroscopy. The mineral is characterised by an intense Raman band at 984 cm(-1), assigned to the (PO4)3- ν1 symmetric stretching mode. A shoulder band at 1037 cm(-1) is attributed to the (SO4)2- ν1 symmetric stretching mode. Two Raman bands observed at 1102 and 1148 cm(-1) are assigned to (PO4)3- and (SO4)2- ν3 antisymmetric stretching modes. Multiple bands provide evidence for the reduction in symmetry of both anions. This concept is supported by the multiple sulphate and phosphate bending modes. Raman spectroscopy shows that there are more than one non-equivalent water molecules in the sanjuanite structure. There is evidence that structural disorder exists, shown by the complex set of overlapping bands in the Raman and infrared spectra. At least two types of water are identified with different hydrogen bond strengths. The involvement of water in the sanjuanite structure is essential for the mineral stability.     

Intramolecular coupling of BrO stretching vibrations in solid bromates, infrared and Raman spectroscopic studies on M(BrO3)2.6H2O (M = Mg, Co, Ni, Zn) and Ni(ClO3)2.6H2O

Infrared and Raman spectra of the isostructural cubic halate hexahydrates M(BrO3)2.6H2O (M = Mg, Co, Ni, Zn) and Ni(ClO3)2.6H2O (space group, Pa3; Z = 4) are presented. They are discussed with respect to the strength of the O-H...OXO2 hydrogen bonds (hydrogen bond acceptor capability, synergetic effect) and the order of the BrO stretching modes. In the case of undistorted bromate ions, e.g. at C3 lattice sites, the order of the symmetric (v1) and asymmetric (v3) XO stretching modes is v1 < v3 as for ClO3- but in contrast to IO3- with v1 > v3. The relative order of v1 and v3 of halate ions is mainly governed by the specific masses of the halogen atoms and the angles of the XO3- ions. The latter decrease in the sequence ClO3- (107degrees) > BrO3-> IO3- (< 100 degrees). The Raman scattering intensities of the asymmetric XO stretching modes v3 of the title compounds are unusually low (< 5% those of v1).     

Infrared multiple photon dissociation spectra of proton- and sodium ion-bound glycine dimers in the N-H and O-H stretching region

The proton- and the sodium ion-bound glycine homodimers are studied by a combination of infrared multiple photon dissociation (IRMPD) spectroscopy in the N-H and O-H stretching region and electronic structure calculations. For the proton-bound glycine dimer, in the region above 3100 cm (-1), the present spectrum agrees well with one recorded previously. The present work also reveals a weak, broad absorption spanning the region from 2650 to 3300 cm (-1). This feature is assigned to the strongly hydrogen-bonded and anharmonic N-H and O-H stretching modes. As well, the shared proton stretch is observed at 2440 cm (-1). The IRMPD spectra for the proton-bound glycine dimer confirms that the lowest energy structure is an ion-dipole complex between N-protonated glycine and the carboxyl group of the second glycine. This spectrum also helps to eliminate the existence of any of the higher-energy structures considered. The IRMPD spectrum for the sodium ion-bound dimer is a much simpler spectrum consisting of three bands assigned to the O-H stretch and the asymmetric and symmetric NH 2 stretching modes. The positions of these bands are very similar to those observed for the proton-bound glycine dimer. Numerous structures were considered and the experimental spectrum agrees with the B3LYP/6-31+G(d,p) predicted spectrum for the lowest energy structure, two bidentate glycine molecules bound to Na (+). Though some of the structures cannot be completely ruled out by comparing the experimental and theoretical spectra, they are energetically disfavored by at least 20 kJ mol (-1).     

Vibrational spectra of mono, di and trimethyl ammonium double sulphates of rare earths Pr, Nd, Ho and Eu

Infrared and Raman spectra of four rare earth (Ho, Eu, Nd and Pr) double sulphates have been recorded and analysed based on the vibrations of methyl ammonium cations, sulphate anions and water molecules. Formation of hydrogen bonds of the type N-H...O and O-H...O are identified in all the compounds. Bifurcated hydrogen bonds are present in the compounds with dimethyl ammonium cations. The sulphate anions are distorted and occupy a lower site symmetry in the compounds. The bands obtained for (CH(3))(2)NH(2) and SO(4)(2-) ions indicate that the structural bonding of (CH(3))(2)NH(2)Eu(SO(4))(2).H(2)O and (CH(3))(2)NH(2)Ho(SO(4))(2).4H(2)O is identical. Electronic transition bands of Eu(3+) and Nd(3+) observed in the Raman spectra of these two compounds have been identified and discussed.     

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.     

Raman spectra of gas hydrates--differences and analogies to ice 1h and (gas saturated) water

It is generally accepted that Raman spectroscopic investigations of gas hydrates provide vital information regarding the structure of the hydrate, hydrate composition and cage occupancies, but most research is focused on the vibrational spectra of the guest molecules. We show that the shape and position of the Raman signals of the host molecules (H(2)O) also contain useful additional information. In this study, Raman spectra (200-4000 cm(-1)) of (mixed) gas hydrates with variable compositions and different structures are presented. The bands in the OH stretching region (3000-3800 cm(-1)), the O-H bending region (1600-1700 cm(-1)) and the O-O hydrogen bonded stretching region (100-400 cm(-1)) are compared with the corresponding bands in Raman spectra of ice Ih and liquid water. The interpretation of the differences and similarities with respect to the crystal structure and possible interactions between guest and host molecules are presented.     

Confocal Raman studies of Mg(NO3)2 aerosol particles deposited on a quartz substrate: supersaturated structures and complicated phase transitions

Individual Mg(NO3)2 aerosol particles deposited on a quartz substrate were investigated by confocal Raman spectroscopy. With decreasing the relative humidity (RH) from 92.0% to 1.8%, Raman spectra were obtained of Mg(NO3)2 droplets with water-to-solute molar ratios (WSRs) from 43.1 to 5.2, as well as of amorphous particles. At WSR < 6.0, contact ion pairs between Mg2+ and NO3(-) occurred abundantly, while at RHs of 2.2% and 1.8% with even lower WSRs, amorphous particles appeared with quasi-lattice structures. Two components, one at 3259.0 cm(-1) (C1) and the other at approximately 3480.0 cm(-1) (C2), were resolved for the water O-H stretching envelope through nonlinear curve fittings. The area ratio of C1 to C2, that is, A1/A2, declined with the decrease of WSR, reflecting the breakage of strong hydrogen bonds induced by the hydration of NO3(-). Curve fittings were also carried out for the water O-H stretching envelope of NaNO3 droplets. The value of A1/A2 for Mg(NO3)2 droplets was always higher than that for NaNO3 droplets at the same WSR, indicating a much stronger "structure-making" effect of Mg2+ than of Na+. In the efflorescence process, aerosol particles followed different paths of phase transition from droplets to Mg(NO3)2.6H2O or amorphous states. Reversing somewhat the phase transitions in the efflorescence process, aerosol particles dissolved into droplets with the increase of RH in the deliquescence process. Heterogeneous particles prepared by dehydrating Mg(NO3)2.6H2O were investigated by the depth profiling technique. About 15 h later, the main body of particles changed into Mg(NO3)2.2H2O, a small quantity of Mg(NO3)2.6H2O scattered around particle edges, and some particles were in amorphous states. About 10 days later, a new solid phase occurred on particle surfaces, while the interiors were still Mg(NO3)2.2H2O. With increasing the RH to approximately 11%, significant Mg(NO3)2.6H2O formed on particle surfaces, covering the interior Mg(NO3)2.2H2O.     

Infrared spectra and electronic structure calculations for the group 2 metal M(OH)2 dihydroxide molecules

Reactions of laser-ablated Mg, Ca, Sr, and Ba atoms with O2 and H2 in excess argon give new absorptions in the O-H and O-M-O stretching regions, which increase together upon UV photolysis and are due to the M(OH)2 molecules (M = Mg, Ca, Sr, and Ba). The same product absorptions are observed in the metal atom reactions with H2O2. The M(OH)2 identifications are supported by isotopic substitution and theoretical calculations (B3LYP and MP2). The O-H stretching frequencies of the alkaline earth metal dihydroxide molecules decrease from 3829.8 to 3784.6 to 3760.6 to 3724.2 cm(-1) in the family series in solid argon, while the base strength of the solid compounds increases. Calculations show that Sr(OH)2 and Ba(OH)2 are bent at the metal center, owing to d orbital involvement in the bonding. Although these molecules are predominantly ionic, the O-H stretching frequencies do not reach the ionic limit of gaseous OH- going down the family group because of cation-anion polarization and p(pi) --> d(pi) interactions.     

Structure and IR spectra of microhydrated Cl2 with an excess electron: experiment versus theory

A working methodology to generate theoretical IR spectra following ab initio electronic structure methods is reported. Theoretical IR spectra of Cl(2)(?-)·nH(2)O clusters (n = 1-5) are generated as a case study. Excellent agreement between the calculated and the reported experimental IR spectra based on size-selected spectroscopy is observed. It is shown that uniform scaling of calculated harmonic frequencies of these hydrated clusters fail to produce accurate IR spectra. Two different scaling factors in two different regions of O-H stretching of solvent water molecules are needed to account for the anharmonic contribution. This observation is also true for Br(2)(?-)·nH(2)O and I(2)(?-)·nH(2)O systems.