Calculations of the vibrational frequency and isotopic shift of UF₆ and U₂ F₆

Molecular structure, vibrational frequency and infrared intensity of UF 6 are investigated by using the revised Perdew-Burke-Enzerhof function with the triple-zeta polarized basis set. The calculation results are in good agreement with the experimental values and indicate the existence of a stable U2F6 molecule with a multiple bonded U2 unit. The calculation results also predict that the D3d symmetry of U2F6 is more stable than D3h . The optimized geometries, vibrational frequencies, and infrared intensities are also reported for U2F6 molecules in D3d symmetry. In addition, the isotopic shift of vibrational frequencies of the two molecules under isotopic substitution of uranium atom are also investigated with the same method. The U2F6 molecule is predicted to be better than UF6 for laser uranic isotope separation.     

D3d distortion in CsUF6

A slight D_3d distortion on the octahedral UF₆^? complex splits the Γ^'₈ and Γ₈ octahedral levels into four doublets. These doublets and other electronic levels of the CsUF₆ ground configuration have been identified according to their vibronic side-bands. In the calculation of the crystal field Hamiltonian, the amount of D_3d distortion on the UF₆^? octahedron is treated as the parameter, Δ. The interactions of the 5f electron of the UF₆^? complex contains five parameters: ξ_5f, B₂⁰, B₄⁰, B₆⁰ and Δ. The calculated energy spectrum and the g-tensor of the ground state show good agreement with the experimental measurements.     

Absorption spectra of C6H6 and C6D6 near 340 nm

The absorption spectra of C₆H₆ and C₆D₆ in the liquid phase have been studied near 340 nm. The absorption spectrophotometric mounting was a sequential double-beam attachment with linear response to energy on scanning of the spectrum before the exit slit and an electronic device which gives directly either the absorbance or the integrated absorbance of a transition and, consequently, its oscillator strength.The oscillator strength measured for the band of C₆H₆ is 8×10^?8, which corresponds to a dipole moment of 2.4×10^?3 Debye; this value is of the same order as a theoretical value calculated by Tsubomura and Mulliken (3.8×10^?3 Debye) for a transition between states ³F and ³A of an oxygen-benzene pair. This agreement corroborates the hypothetical existence of such a transition.The first vibrational band is at 28553 cm^?1 for C₆H₆; this band is not observed in the vapor or solid phase. It corresponds probably to the transition 0-0, which is considered in the literature to be near 29500 cm^?1. The isotopic shift measured for this first band is 164 cm^?1. The vibrational frequencies are, respectively, 910 cm^?1 for C₆H₆ and 889 cm^?1 for C₆D₆.     

I.R. absorption due to H− and D− Ions in BaClF and SrClF

The i.r. absorption spectra sssociated with the vibrations of H^? and D^? ions in SrClF and BaClF have been studied in the range 600–2000cm^?1.The U centers are in fluorine sites. Because of the D_2d symmetry of the fluorine site, the triple degeneracy of the U center local mode in crystals of cubic symmetry, is split in BaClF and SrClF. In these crystals (space group D⁷_4h) unlike what happens with the cubic crystals, the symmetry types of the lattice band modes which give rise to the local mode sidebands, can be known experimentally. These band modes are almost only of E symmetry type. The E symmetry modes involve a vibration of the U center.A calculation of the local mode frequencies in BaClF:H^? from the experimental one in BaF₂:H^?, has been performed. An H^? ion shell model is more adequate than a rigid ion model to account for the frequencies and the relative intensities of the localized vibrational lines. The best agreement is obtained when the shell charge and the crystal polarizability of the H^? ion in BaF₂ are respectively ?1.3 e and 2.6 ų.     

Geometrical structures,vibrational frequencies,force constants and dissociation energies of isotopic water molecules （H2O,HDO, D2O,HTO, DTO,and T2O） under dipole electric field

The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86/6-311++G(3df,3pf). The results show that when the dipole electric fields change from -0.05 a.u. to 0.05 a.u., the bond length of H-O increases whereas the bond angle of H-O-H decreases because of the charge transfer induced by the applied dipole electric field. The vibrational frequencies and the force constants of isotopic water molecules change under the influence of the strong external torque. The dissociation energies increase when the dipole electric fields change from -0.05 a.u. to 0.05 a.u. and the increased dissociation energies are in the order of H2O, HDO, HTO, D2O, DTO, and T2O under the same external electric fields.     

Measurements of235U/238U isotopic ratio in the photoproduct UF5 by multiphoton ionization and time-of-flight mass spectrometry

A MultiPhoton-Ionization Time-Of-Flight Mass Spectrometry (MPI/TOFMS) apparatus was developed for real-time measurement of the uranium isotopic ratio in nascent UF₅ formed by the 266 nm photolysis of effusive UF₆ ( < 300 K, 1.3 × 10^–4 Pa). The UF₅ was selectively and efficiently multiphoton ionized by 532 nm radiation at appreciably low fluences ( < 10 J/cm²). The main ions observed, U⁺ and U²⁺, were subsequently analyzed with a TOFMS with mass resolution of 1190 to separate²³⁵U ⁿ⁺ and²³⁸U ⁿ⁺ completely. The isotopic ratio measurements showed good precision resulting from the excellent agreement which was observed between the isotopic ratios in UF₅ products and those in a parent UF₆ sample. These results suggested that the MPI/TOFMS method can be applied to the real-time analysis of separation factors in the molecular laser isotope separation of uranium by ionization of UF₅ following the infrared photodissociation of UF₆.     

Vibration-rotation spectra and molecular force field of methylene fluoride and methylene fluoride-d2

Infrared spectra of CH₂F₂ and CD₂F₂ have been measured under a medium resolution. The vibration-rotation bands of CD₂F₂ fundamentals have been analyzed and the assignment for the fundamentals of CD₂F₂ is given. In addition, a number of overtone and combination bands are observed for CH₂F₂, which helps to clarify the vibrational assignment for CH₂F₂. A normal coordinate treatment has been carried out: The force constants in a modified Urey-Bradley as well as the general valence force fields have been determined, the vibrational frequencies and the centrifugal distortion constants obtained from microwave spectroscopy being used. The force constants of the methylene fluoride molecule are discussed in connection with those of the related molecules. Special features of the CH₂F₂ and CD₂F₂ spectra are also described.     

BeH,H2和BeH2的分子结构和势能函数

用二次组态相关(QCISD)和密度泛函(B3LYP)方法, 选用6-311++g(d,p), 6-311++g(3df,3pd)和D95(3df,3pd)基组对H₂, BeH和BeH₂分子的结构进行优化. 得到它们的基态电子态分别为H₂(¹Σ_g), BeH(²Σ)和BeH₂(¹Σ_{g 关键词： BeH 2}')" href="#">BeH₂ 2')" href="#">H₂ 二次组态相关(QCISD) 势能函数     

The Raman,Infrared and Proton NMR Spectra and the Structures of Dimethyl Chalcogenides

The vibrational bands of dimethyl chalcogenides (CH₃-X-CH₃) (X = O,S,Se,Te) have been assigned on the basis of C_2V symmetry by most of previous workers.^1–13) On the other hand, some ones have assigned D^3d to these molecules ^14–15) and to structurally related compounds; SiH₃-O-SiH₃ ¹⁶), CH₃-Hg-CH₃ ¹⁷), CF₃-Hg-CF₃ ¹⁸) and Cl₃Si-O-SiCl₃ ¹⁹). The symmetry of ethane(CH₃-CH₃) is obviously D_3d ²⁰⁾, because the vibrational spectra which indicate the lack of coincidence between Raman and infrared frequencies can be explained based upon D_3d symmetry, and the bent c c should theoretically be impossible. The CH₃-X-CH₃ molecules are considered as a derivative in which CH₃ group is connected to CH₃ in opposite direction along the z axis and x atom is inserted between the two CH₃ groups. Consequently, for a linear C-X-C model, the vibrational spectra of CH₃-X-CH₃ ^14,15) should be similar to those of CH₃-CH₃, except being added C-O-C stretching and bending bands. The obtained spectra of CH₃-X-CH₃ ^14,15) show a marked correspndence to that of ethane, and indicate that the rule of mutual exclusion holds between Raman and infrared frequencies. Therefore the symmetry of CH₃-X-CH₃ Seems to be D_3d, But mst of the previom papers ^1–13) have assigned C_2v to CH₃-X-CH₃ as mentioned above.     

BH2和AlH2分子的结构及其解析势能函数

运用二次组态相关(QCISD)方法，分别选用6-311++G(3df,3pd)和D95(3df,3pd)基组，对BH₂和AlH₂分子的结构进行了优化计算，得到BH₂分子的稳态结构为C_2v构型，电子态为²A₁、平衡核间距R_BH=0.1187nm、键角∠HBH=128.791°、离解能D_e=3.65eV、基态振动频率ν₁(a₁)=1020.103cm^-1,ν₂(a₁)=2598.144cm^-1,ν₃(b₂)=2759.304cm^-1.AlH₂分子的稳态结构也为C_2v构型，电子态为²A₁、平衡核间距R_AlH=0.1592nm、键角∠HAlH=118.095°、离解能D_e=2.27eV、基态振动频率ν₁(a₁)=780.81cm^-1,ν₂(a₁)=1880.81cm^-1，ν₃(b₂)=1910.46cm^-1.采用多体项展式理论推导了基态BH₂和AlH₂分子的解析势能函数，其等值势能图准确再现了BH₂和AlH₂分子的结构特征及其势阱深度与位置.分析讨论势能面的静态特征时得到BH+H→BH₂反应中存在鞍点，活化能为150.204kJ/mol；AlH+H→AlH₂反应中也存在鞍点，活化能为54.8064kJ/mol. 关键词： 2')" href="#">BH₂ 2')" href="#">AlH₂ Murrell-Sorbie函数 多体项展式理论 解析势能函数     

Absolute Raman intensities of CH4, CH3D,CH2D2, CHD3, and CD4

Measurements of the absolute vibrational Raman intensities and depolarization ratios for the fundamental and some overtone and combination bands of CH₄, CH₃D, CH₂D₂, CHD₃, and CD₄ are reported. Experimental aspects of these measurements are discussed. The experimental data conform satisfactorily to all isotope intensity sum rules. The measured intensities and depolarization ratios, together with the vibrational potential function for CH₄, make possible the calculation of the four independent parameters of the isotopic invariant quantities $\text{α}{}^{\mathrm{S}}\text{= |}\text{?α}\text{?S}\text{|}$. The results deduced from these agree with all 36 experimentally observed values. Values of electro-optical parameters for the CH bond are calculated and discussed.     

Structural and vibrational properties of Ca2FeH6 and Sr2RuH6

The structural and vibrational properties of the isostructural compounds Ca₂FeH₆ and Sr₂RuH₆ are determined by periodic DFT calculations and compared with their previously published experimental crystal structures as well as new experimental vibrational data. The analysis of the vibrational data is extended to the whole series of alkaline-earth iron and ruthenium hydrides A₂TH₆ (A=Mg, Ca, Sr; T=Fe, Ru) in order to identify correlations between selected frequencies and the T-H bond length. The bulk moduli of Ca₂FeH₆ and Sr₂RuH₆ have also been determined within DFT. Their calculated values prove to compare well with the experimental values reported for Mg₂FeH₆ and several other compounds of this structure.     

Coherent Raman spectra of the ν1 mode of BF3 and BF3

High resolution (0.001 cm⁻¹) coherent anti-Stokes Raman spectroscopy (CARS) was used to directly examine the ν₁ symmetric stretching mode of the planar symmetric D_3h molecules ¹⁰BF₃ and ¹¹BF₃. Simulations of the spectra were done using ν₁ rovibrational parameters deduced from published infrared hot-band and difference-band studies and the close similarity to the observed CARS spectra confirms the validity of the infrared constants. No significant perturbations by Fermi resonance or Coriolis interactions with nearby states are observed, in marked contrast to the case of sulfur trioxide, a similar D_3h molecule recently studied. In the harmonic approximation, the ¹⁰BF₃ and ¹¹BF₃ν₁ Q-branches would be identical since the isotopic substitution is at the center of mass but, interestingly, the ν₁ stretching frequency for ¹¹BF₃ is found to be 0.198 cm⁻¹higher than for the lighter ¹⁰BF₃ isotopomer. This counterintuitive result is reproduced almost exactly (0.200 cm⁻¹) by ab initio calculations (B3LYP/cc-pVTZ) that included evaluation of cubic and quartic force constants and x_ij anharmonicity constants. The ab initio computations also predict to within 1% the ΔB, ΔC changes in the rotational constants in going from the ground state to the v₁ = 1 vibrational level. The results illustrate nicely the complementary interplay of modern infrared, Raman, and ab initio methods in obtaining and analyzing rovibrational spectra.     

Improved infrared and visible emission spectra of the H3 and D3 molecules

Better-resolved Rydberg-Rydberg emission spectra of the neutral H₃ and D₃ molecules in the infrared and visible regions, with less interference from H₂ and D₂ emission, have been obtained by using a Droege-Engelking type of corona discharge source. Using nl_λ notation, the lower electronic states are 3p₁ in the infrared and 2p₀ in the visible, and the upper electronic states are mixed (3s,3p₀,3d₀,3d₁,3d₂) states. In particular, a line near 16 842 cm⁻¹ in H₃, previously obscured by an H₂ line, reveals a (3s,3d) interaction that is confirmed by other lines. The spectra are analysed including this interaction. However, fits to effective Hamiltonians still have relatively large standard deviations, probably partly due to poor convergence of the rotational expansions and partly due to many small perturbations of the levels by background states.     

First-principles electronic transport properties study of small carbon clusters: Cyclic C6

The transport properties of the six-atom carbon ring cluster C₆ sandwiched between Al(100) electrodes have been investigated by first-principles nonequilibrium Green's function technique. Our results demonstrate that the transport properties of monocyclic C₆ with D3h symmetry, with alternating bond angles, the most stable C₆ isomer, show metallic conductance. The charge transfer between the central molecule and the electrodes is very important for its transport properties. We also compare the equilibrium transmission spectra for C₆ in different isomers.     

The structural and spectroscopic properties for uranium oxides

The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO 2 , UO 3 , and U 2 O 3 molecules are systematically investigated using the density functional theory (DFT) with the method of generalized gradient approximation (GGA). The bond lengths and the vibrational frequencies of the ground states of UO, UO 2 , and UO 3 molecules are all in agreement with available experimental data. For U 2 O 3 molecules, our calculations indicate that the ground state of the U 2 O 3 molecule is an X 7 A ′ 1 state with D 3h (trigonal bipyramid) symmetry (R 1 (U–O)=0.2113 nm, R 2 (U 1 –U 2 )=0.2921 nm, ∠U 1 OU 2 = 87.5 , dihedral angle Θ(U,O 1 ,O 2 ,O 3 )=62.40 ). The harmonic frequency, the IR intensity and the spin density of the U 2 O 3 molecule are all obtained for the first time in theory. For the ground state of U 2 O 3 molecules, the vibrational frequencies are 178.46 (A ′ 1 ), 276.79 (E ′′ 1 ), 310.77 (E ′ 1 ), 396.63 (A ′′ 2 ), 579.15 (E ′ 1 ), and 614.98 (A ′ 1 ) cm 1 . The vibrational modes corresponding to the IR maximum peaks are worked out for UO 3 and U 2 O 3 molecules. Besides, the results of Gophinatan–Jug bond order indicate that UO, UO 2 , and UO 3 molecules possess U=O double bonds and that the U 2 O 3 molecule possesses U–O single bonds and a U–U single bond.     

Vibrational study of H3OUO2PO4 · 3 H2O (HUP) and related compounds. phase transitions and conductivity mechanisms: part I,KUO2PO4 · 3 H2O (KUP)

Infrared and Raman spectra of polycrystalline KUO₂PO₄ · 3 H₂O (KUP) and its isotopic derivatives KUO₂P¹⁸O₄ · 3 H₂O and KUO₂PO₄ · 3 D₂O have been investigated in the 4000-10-cm^?1 range at different temperatures. An assignment of the bands in terms of UO₂, PO₄ and H₂O vibrations has been proposed. Combined differential scanning calorimetry and spectroscopic data show two diffuse phase transitions near 130 and 230 K. Comparison of the vibrational spectra of phase I at 300 K and phase IV at 100 K indicates that ordering of the water molecules with subsequent ordering of PO₄ tetrahedra on a site with lower symmetry appears to be the main mechanism responsible for the phase transformation. All the six O-H distances of water molecules in phase IV are found to be crystallographically nonequivalent. Conducting ion frequencies and the corresponding force constants have been determined for the analogous compounds MUP with M = K⁺, Na⁺, Ag⁺, NH⁺₄, Tl⁺ and H₃O⁺ and compared with other properties of these ionic conductors. Conductivity mechanisms in these materials are discussed.     

Laser study of the photophysical properties of UF6

The purpose of this paper is to review the most relevant theoretical and experimental results reported in recent years, on the photophysical properties of the uranium hexafluoride molecule in the gas phase. Details of the structure of the molecular orbitals of UF₆ are discussed with reference to theoretical calculations of the electronic states. Tentative assignments of the electronic transitions in the experimental visible-uv absorption spectrum are also considered. The fluorescence properties of the excited states of UF₆ are critically reviewed. The use of laser beams to excite the fluorescence emission of UF₆ is shown to be a fruitful experimental technique. The measurement of fluorescence parameters (i.e. the emission and excitation spectra, the decay time and quantum yield) is a particularly valuable and sensitive way of studying the dynamics and structure of the excited electronic states. The different mechanisms of fluorescence quenching that have been proposed are also critically reviewed.     

High-resolution FTIR spectrum and analysis of the ν2+ν4 combination band of SF6

The spectroscopic knowledge of sulfur hexafluoride, which is necessary for a correct remote sensing and monitoring of this species in the Earth’s atmosphere, is still very partial. In particular, the hot bands in the strongly absorbing ν₃ region (near 948 cm⁻¹) have not been analyzed yet. Their study implies the analysis of many vibrational levels and thus the spectroscopy of various fundamental, harmonic, and combination bands. The present work is a new contribution to this topic, concerning the ν₂+ν₄ combination band. The FTIR spectrum of this region has been recorded at room temperature with a resolution of 0.002 cm ⁻¹. The data have been analyzed thanks to the HTDS software (http://www.u-bourgogne.fr/LPUB/shTDS.html) developed in Dijon for XY₆ octahedral molecules. Seven hundred and fifty-nine lines could be assigned up to J=112, and the standard deviation is 0.0022 cm⁻¹. The distance between the two vibrational sublevels with respective symmetry F_1u and F_2u is 0.348 cm⁻¹.     

Vibration-internal rotation-rotation Hamiltonian of an asymmetric top molecule with C3v internal rotor

An expression for the kinetic energy part of the vibration-torsion-rotation Hamiltonian of an asymmetric top molecule containing a C_3v internal rotor has been derived. The terms for various interactions in the molecule, viz. Coriolis interaction between rotation (both overall and internal rotation) and vibration, centrifugal distortion and anharmonicity of molecular vibrations induced by the internal, and overall rotation of the molecule, have been formulated. For a planar molecule with C_s symmetry we have obtained the vibrationally averaged rotation-internal rotation Hamiltonian. Diagonalization of this Hamiltonian for a particular vibrational state will yield the rotation-internal rotation energy levels and hence the transition frequencies. These data will be useful for analysis of high-resolution infrared spectra obtained by laser or Fourier transform spectroscopy of nonrigid molecules with internal rotor. We also present a set of quartic centrifugal distortion coefficients associated with rotation and internal rotation. These data will be helpful for evaluation of vibrational potential constants of the orthorhombic asymmetric top molecules.