Fourier transform infrared study of perchlorate (ClO4 and ClO4) anions isomorphously isolated in potassium permanganate matrix. Vibrational anharmonicity and pseudo-symmetry effects

Fourier transform infrared spectra of isotopomeric ³⁵ClO₄⁻ and ³⁷ClO₄⁻ anions isomorphously isolated in potassium permanganate matrix were recorded at room and low temperature (LT, ∼100 K). On the basis of the detected second-order vibrational transitions involving the dopant species ν₃ mode components, anharmonicity constants and harmonic eigenvalues for these modes were calculated. Although the overall appearance of the region of fundamental vibrational transitions in the spectra of dopant perchlorate anions may be better explained in terms of a pseudo-symmetry (the so-called ‘latent’ symmetry) site group C_2v, corresponding to the pseudo-symmetry space group Imma, instead of the (rigorous) crystallographic C_s one (corresponding to the crystallographic Pnma space group), an opposite statement seems to be valid for the region of the second-order vibrational transitions. The vibrational mode mixing (a ‘Fermi-like’ resonance) of the ClO₄⁻ ν₁ mode with the ν_3a site group component is almost negligible.     

Density Functional Theory Calculations of Normal Modes and Infrared Intensities for Tetraazaporphin

By the DFT/B3LYP method with a 6-31G(d) basis set, the structure, normal vibration frequencies, and band intensities in the IR spectra of porphin, tetraazaporphin (TAP), and three of its isotopomers have been calculated. Scaling of the force constants for porphin vibrations in nonredundant natural coordinates has been performed. The obtained scaling factors are used to predict the force field and normal modes of TAP and three of its isotopomers. To carry out a reliable assignment of the TAP frequencies, two alternative methods have been used: a wavenumber-linear scaling method and the frequency-shift method. There is good agreement between the frequencies predicted by the three methods used. The IR absorption spectrum of TAP has been simulated. Assignments of the observed experimental frequencies of TAP of odd symmetry types are suggested.     

Application of a method of linear scaling of frequencies in calculations of the normal vibrations of polyatomic molecules

The frequencies of the harmonic vibrations of 88 compounds consisting of atoms of the first period are calculated in the approximation of the hybrid density functional B3LYP with the 6-31G* basis set. Using 1189 frequencies from experimental IR and Raman spectra of these compounds in the gas phase and the corresponding theoretical frequencies, the coefficients of the function of linear scaling are found by the least squares method. The method of linear scaling of frequencies is applied to the prediction of the 108 vibrational frequencies of a porphin molecule. A conclusion is made that this method is promising for the interpretation of vibrational spectra of complex molecules and, in combination with the Pulay method of scaling of a quantum-mechanical field, for the determination of harmonic force constants.     

The structure and vibrational spectral parameters of a complex of HF with the planar (H<Subscript>2</Subscript>CO)<Subscript>2</Subscript> dimer

Equilibrium nuclear configurations of the planar formaldehyde homodimer (H₂CO)₂ and the (H₂CO)₂···HF complex are determined in the MP2/6-311++G(3df, 3pd) approximation taking into account the superposition error of basis sets of monomers. Harmonic values of the frequencies and intensities of fundamental transitions between vibrational states of these hydrogen-bonded complexes were calculated using the Gaussian 09 package of programs. Anharmonic values of the frequencies and intensities of the ν(H–F) stretching vibration and several intermolecular vibrations in the (H₂CO)₂···HF trimer were obtained from variational solutions of one-, two-, and three-dimensional vibrational Schrödinger equations. The anharmonic influence of the C=O and hydrogen bond O···H–F stretching vibrations, as well as of librational vibrations of monomers, on the spectral parameters of the strongest ν(H–F) absorption band of trimer was studied.     

A Raman spectroscopic study of the different vanadate groups in solid‐state compounds—model case: mineral phases vésigniéite [BaCu3(VO4)2(OH)2] and volborthite [Cu3V2O7(OH)2·2H2O]

Raman spectroscopy has been used to study vanadates in the solid state. The molecular structure of the vanadate minerals vésigniéite [BaCu₃(VO₄)₂(OH)₂] and volborthite [Cu₃V₂O₇(OH)₂·2H₂O] have been studied by Raman spectroscopy and infrared spectroscopy. The spectra are related to the structure of the two minerals. The Raman spectrum of vésigniéite is characterized by two intense bands at 821 and 856 cm⁻¹ assigned to ν₁ (VO₄)³⁻ symmetric stretching modes. A series of infrared bands at 755, 787 and 899 cm⁻¹ are assigned to the ν₃ (VO₄)³⁻ antisymmetric stretching vibrational mode. Raman bands at 307 and 332 cm⁻¹ and at 466 and 511 cm⁻¹ are assigned to the ν₂ and ν₄ (VO₄)³⁻ bending modes. The Raman spectrum of volborthite is characterized by the strong band at 888 cm⁻¹, assigned to the ν₁ (VO₃) symmetric stretching vibrations. Raman bands at 858 and 749 cm⁻¹ are assigned to the ν₃ (VO₃) antisymmetric stretching vibrations; those at 814 cm⁻¹ to the ν₃ (VOV) antisymmetric vibrations; that at 508 cm⁻¹ to the ν₁ (VOV) symmetric stretching vibration and those at 442 and 476 cm⁻¹ and 347 and 308 cm⁻¹ to the ν₄ (VO₃) and ν₂ (VO₃) bending vibrations, respectively. The spectra of vésigniéite and volborthite are similar, especially in the region of skeletal vibrations, even though their crystal structures differ. Copyright © 2011 John Wiley & Sons, Ltd.     

High-Resolution FTIR Spectra of CD2Cl2: Analysis of the ν3/ν7/ν9 Triad

The infrared spectra of isotopically pure CD₂³⁵Cl₂ have been recorded at a resolution of 0.0026 cm⁻¹ (FWHM) in the range 600-1160 cm⁻¹ with a Bruker IFS 120 HR Fourier transform interferometer. The absorption between 670 and 750 cm⁻¹ is due to three fundamentals, ν₃ (weak), ν₇ (very weak), and ν₉ (strong). A satisfactory analysis of the observed spectra has been obtained by including a c-Coriolis coupling between ν₃ and ν₉ and a b-Coriolis term between ν₇ and ν₉. Although no transitions could be observed for the very weak ν₇ band, its band origin could be estimated from the Coriolis interaction with ν₉. From the analysis of about 4200 assigned transitions of the ν₃ and ν₉ bands, excited state constants have been determined up to sextic terms. The Coriolis parameters obtained are compared to those calculated from a harmonic force field.     

The angleICI Bending Satellites in the Millimeter-Wave Rotational Spectra of CH(2)I(2) and CD(2)I(2)

Rotational transitions in the first four excited states of the low-frequency angleICI bending mode, nu(4), have been assigned in the mm-wave rotational spectra of CH(2)I(2) and of CD(2)I(2). Measurements of transition frequencies, made over the frequency region 167-326 GHz and for J" up to 190, allowed determination of sextic level spectroscopic constants for all states. The changes in spectroscopic constants with vibrational excitation show very small anharmonicity, in spite of the very low frequency of this mode (121 cm(-1)). Vibrational excitation affects the moments of inertia in such a way that the planar moment P(b), about the plane perpendicular to both angleICI and angleHCH, is practically invariant. Vibrational change in P(c), the moment along the principal axis in the HCH plane and perpendicular to the angleHCH bisector, has been successfully reproduced with an ab initio harmonic force field so that there is no discernible vibrational change in angleHCH on excitation of angleICI. Finally, the change in P(a) leads to estimated vibrational change of +0.12 degrees in the value of angleICI itself. Copyright 2000 Academic Press.     

Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO₃OH)· 2H₂O. The mineral is characterised by an intense Raman band at 865 cm⁻¹ assigned to the ν₁ (AsO₃)²⁻ symmetric stretching mode. The equivalent IR band is found at 864 cm⁻¹. The low‐intensity Raman bands in the range from 844 to 886 cm⁻¹ provide evidence for ν₃ (AsO₃) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm⁻¹ region are attributed to ν₂ and ν₄ (AsO₃) bending modes. Prominent Raman bands at around 3187 cm⁻¹ are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm⁻¹ to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO₃OH)²⁻ units. Copyright © 2009 John Wiley & Sons, Ltd.     

The adiabatic approximation as a diagnostic tool for torsion-vibration dynamics

The adiabatic separation of large-amplitude torsional motion from small-amplitude vibrations is applied as an aid in interpreting the results of fully coupled quantum calculations on a model methanol Hamiltonian. Comparison is made with prior work on nitromethane [D. Cavagnat, L. Lespade, J. Chem. Phys. 106 (1997) 7946]. Even though the torsional potentials are very different, both molecules show a transition from adiabatic to diabatic behavior when the CH stretch is excited to ν_CH = 4 or higher. In the adiabatic approximation, the effective torsional potentials for the various CH stretch vibrational states do not cross, but the CH vibrational amplitude moves from one bond to the next as a function of torsional angle. In the diabatic approximation, the effective torsional potentials do cross, but the distribution of the CH vibrational amplitude remains approximately constant in the vicinity of the crossing. The transition to diabatic behavior is promoted by the normal mode to local mode transition, and the relevant adiabatic and diabatic effective torsional potentials are determined by the torsion-vibration coupling. The torsion-vibration couplings in the four overtone manifolds considered (methanol OH, CH, nitromethane CH, and hydrogen peroxide OH) are large, reaching 265-500 cm⁻¹ by ν_XH = 6, and are of generally similar magnitude. The largest torsion-vibration couplings involve the first Fourier term in the torsional angle (cosγ for the CH stretch in methanol and the OH stretch in HOOH), whereas higher Fourier terms (cos2γ in nitromethane and cos3γ for the OH stretch of methanol) result in somewhat weaker coupling. Nonadiabatic matrix elements in methanol couple the torsional and vibrational energies and they exhibit a slow fall-off with coupling order.     

Analysis of ν2, ν4 Infrared Hot Bands of SO3: Resolution of the Puzzle of the ν1 CARS Spectrum

Further analysis of the high-resolution (0.0015 cm⁻¹) infrared spectrum of ³²S¹⁶O₃ has led to the assignment of more than 3100 hot band transitions from the ν₂ and ν₄ levels to the states 2ν₂ (l=0), ν₂+ν₄ (l=±1), and 2ν₄ (l=0,±2). These levels are strongly coupled via Fermi resonance and indirect Coriolis interactions to the ν₁ levels, which are IR-inaccessible from the ground state. The unraveling of these interactions has allowed the solution of the unusual and complicated structure of the ν₁ CARS spectrum. This has been accomplished by locating over 400 hot-band transitions to levels that contain at least 10% ν₁ character. The complex CARS spectrum results from a large number of avoided energy-level crossings between these states. Accurate rovibrational constants are deduced for all the mixed states for the first time, leading to deperturbed values of 1064.924(11), 0.000 840 93(64), and 0.000 418 19(58) cm⁻¹ for ν₁, α₁^B, and α₁^C, respectively. The uncertainties in the last digits are shown in parentheses and represent two standard deviations. In addition, new values for some of the anharmonicity constants have been obtained. Highly accurate values for the equilibrium rotational constants B_e and C_e are deduced, yielding independent, nearly identical values for the SO r_e bond length of 141.734 03(13) and 141.732 54(18) pm, respectively.     

Rotational Spectrum of the Excited Vibrational States of DCOOH and Assignment of Optically Pumped Laser Transitions

The rotational spectrum of DCOOH in the 175–335 GHz region was investigated. Analysis of the spectrum made it possible to assign several dozen transitions in the ν₆, ν₈, and ν₅vibrational states and to determine the rotational and centrifugal distortion constants. The derived parameters of the ν₆state allowed four optically pumped laser transitions to be assigned. In addition, the ground state parameters for DCOOH and D¹³COOH have been improved and for the first time those for DC¹⁸OOH and DCO¹⁸OH have been obtained.     

Die Eigenschwingungen des Metall-Hydratkomplexes in BeSO4·4H2O und BeSO4·4D2O

Infrared reflection spectra of single crystals of BeSO₄·4H₂O and BeSO₄·4D₂O have been obtained in polarized light at 300°K and at 14°K in the region between 4000 cm^?1 and 300 cm^?1. By a Kronig-Kramers analysis, the frequencies of the infrared active transitions have been calculated. These transitions are attributed to internal vibrations of the water molecules and sulfate ions and, in the region between 1000 cm^?1 and 300 cm^?1, especially to internal and external vibrations of the tetrahedral Be⁺⁺·4aqu-complexes. The vibrational modes of these complexes consist of a superposition of translational and librational modes of the water molecules and translational modes of the central Be⁺⁺-ion. The vibrational frequencies and normal modes of this complex have been calculated in a central-force model, and force-constants have been determined by fitting the calculated frequencies to the observed spectra. The calculations have shown that the modes, which comprise mainly translational motions of the water molecules, are strongly coupled with librational motions of the water molecules. On the other hand, there exist pure librational modes with practically no admixture of translational motions. The optimum sets of force constants for the BeSO₄·4H₂O crystal and the BeSO₄·4D₂O crystal differ in a manner which can be understood under the assumption that the dimensions of the Be(D₂O)₄ complex are about 0.1 Å larger than those of the Be(H₂O)₄ complex. Some arguments supporting this conclusion will be discussed.     

Density-Functional Theory Calculations of Normal Modes and Raman Intensities for Tetraazaporphin

The structure, harmonic frequencies, and nonresonance Raman intensities for porphin, tetraazaporphin (TAP), and three of its isotopomers are calculated by the density-functional theory of B3LYP/6-31G(d). Scaling of force constants for porphin in nonredundant natural coordinates is performed. The scaling factors obtained were used to predict the force field and normal modes of TAP and three of its isotopomers. Two alternative methods are used to carry out reliable assignment of the TAP frequencies: wavenumber-linear scaling method and frequency-shift method. There is good agreement between the frequencies predicted within the framework of the three methods used. The conservativeness of the out-of-plane B _2g - and B _3g -modes for porphin and TAP is examined. The Raman spectrum for TAP is simulated. A refinement of the assignment of the experimental frequencies for TAP of even symmetry types on the basis of the calculations performed is made.     

The anharmonic force fields of PH3, PHF2, PF3, PH5, and H3PO

The cubic and quartic force fields of the title compounds are determined from ab initio SCF calculations using 6-31G^** and TZP/TZ2P basis sets. The computed geometries, vibration-rotation interaction constants, l-doubling constants, anharmonicity constants, and vibrational wavenumbers are compared with the available experimental data, especially for PH₃ and PF₃. Many experimentally unknown spectroscopic constants are predicted. A scaling procedure based on calculated harmonic and anharmonic force fields is proposed for predicting the vibrational wavenumbers of unknown molecules such as PH₅.     

Overtone spectroscopy of some benzaldehyde derivatives

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm⁻¹ region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect. It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the case of o-disubstituted benzenes it is only 80% of the para-substituted shift.     

Theoretical Interpretation of the Vibrational Spectra of Carboxylic-Acid Dimers in the High-Frequency Range

An anharmonic band shift in the vibrational spectra of carboxylic-acid dimers is estimated on the basis of ab initio quantum calculations of anharmonic force constants. The implementation of ab initio quantum calculations taking into account the anharmonic nature of vibrations is connected with the choice of the atomic basis in the framework of a specific quantum method. All these factors together with the exclusion principle for bands in the infrared and Raman scattering spectra allow identification of the position of the bands of valence vibrations of CH bonds in the range of 2500–3500 cm^–1. The results of model calculations give reason to assert that the fundamental vibrations of the carboxylic fragment are the characteristic frequency and vibrational mode and, for OH bonds, also the characteristic intensity. Small doublet splitting and the exclusion principle for frequencies allow identification of the valence vibrations of CH bonds.     

Vibrational combination states of polyatomic molecules investigated by ultrashort two-pulse spectroscopy

A first infrared pulse at frequency ν₁ generates transitions to intermediate states in S₀ and a simultaneous visible pulse at ν₂ raises the excited molecules to a state in S₁. Tuning the frequencies ν₁ and ν₂ over several hundred wave numbers and holding the sum ν₁ + ν₂ constant allows the observation of various combination vibrations. The technique is demonstrated on polyatomic molecules consisting of 42 atoms.     

The ν2+ν4 Band of Carbonyl Fluoride

We have measured and fitted over 600 lines in the ν₂+ν₄ combination band of COF₂. The spectrum is well reproduced by extrapolation of rotational constants from the ν₂ and ν₄ fundamentals, with no evidence of significant perturbation. The band centre of 2195.272 15(11) cm⁻¹ permits an estimate of −11.32 cm⁻¹ for the anharmonicity constant x₂₄.     

Collective states fed by weak α-transitions in the 230U chain

The ²³⁰U decay chain has been investigated using Ge(Li) spectrometers in singles and coincidence measurements. The internal-conversion spectra have been studied in a β-spectrometer with a Si(Li) detector placed in a homogeneous magnetic field. A total of 31 γ-ray transitions, 14 of which have not been reported before, have been observed in the decay of ²³⁰U and its descendants. All transitions could be unambiguously placed in the individual level schemes. The new band-heads at 805 and 914 keV in ²²⁶Th and ²²²Ra, respectively, are proposed as 0⁺ quadrupole-pairing vibrations. No evidence has been found for the existence of 0⁺ two-phonon harmonic octupole states in these nuclei. A possible anharmonicity of the octupole vibrations is discussed.