On assignment of fundamental vibrational modes of hypophosphite anion and its deuterated analogue

Results of ab initio and density functional theory calculations on the structure and vibrational frequencies of hypophosphite anion indicate earlier experimental assignments of the fundamental vibrational modes are correct while the recent reassignments of several modes proposed by Bickley et al. are inconsistent with the calculated results.     

Structural and spectroscopic studies of LaPO4:Ce/Tb@LaPO4@SiO2 nanorods: Synthesis and role of surface coating

Highly fluorescent LaPO₄:Ce/Tb@LaPO₄@SiO₂ (core/shell/Si) nanorods(NRs) were fabricated with an average length 100 nm by co-precipitation process at low temperature. X-ray diffraction (XRD), Transmission electron microscopy (TEM), energy dispersive X-ray analysis, Fourier transform infrared, optical absorption and photoluminescence spectral techniques were applied to investigate the crystal structure, phase purity, morphology, surface chemistry and optical properties of the as-prepared samples. XRD results confirmed the formation of highly crystalline with single phase, monoclinic type structure. TEM image illustrates the poly-dispersed, narrow size distributed, irregular size rod-shaped nanostructures, with mean diameters of 20 nm and average lengths up to 140 nm. FTIR spectral analysis confirmed the silica surface modification. The comparative emission spectral study shows highest luminescence intensity of core/shell NRs, due to a reduction in nonradiative transition rate. The emission intensity enhancement proves that growing of an inert LaPO₄ layer on the surface of luminescent core-NRs was an effective way to suppress surface related quenching mechanism. These well crystalline, highly aqueous soluble along with extraordinary colloidal stability core/shell/Si NRs were extremely suitable material in fluorescent bio-labeling applications.     

Equilibrium bond lengths, force constants and vibrational frequencies of MnF2, FeF2, CoF2, NiF2, and ZnF2 from least-squares analysis of gas-phase electron diffraction data

The least-squares analysis of the electron diffraction data for MnF₂, FeF₂, CoF₂, NiF₂ and ZnF₂ was carried out in terms of a cubic potential function. The obtained equilibrium bond lengths (in Å) are r_e(Mn–F)=1.797(6), r_e(Fe–F)=1.755(6), r_e(Co–F)=1.738(6), r_e(Ni–F)=1.715(7), and r_e(Zn–F)=1.729(7). The determined force constants and the corresponding vibrational frequencies are listed. The bond length r_e(Cu–F)=1.700(14) Å for CuF₂ was estimated and the variations of bond lengths for the first-row transition metal difluorides were discussed in light of their electronic structure.     

A theoretical study on the ionization of OCS with an analysis of vibrational structures of the photoelectron spectrum

 Ab initio calculations have been performed to study the molecular structures and vibrational levels of the four low-lying ionic states (1, 2²Π, and 1, 2²Σ⁺) of carbonyl sulfide. The global regions of the potential-energy surfaces have been obtained by multireference single and double excitation configuration interaction calculations. Vibrational calculations using explicit vibrational Hamiltonians have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of the four ionic states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states are also presented and are compared with the photoelectron spectrum. Received: 20 January 2001 / Accepted: 22 August 2001 / Published online: 30 October 2001     

Theoretical study of silicon–sulfur clusters (SiS2)n (n = 1–6)

 The possible geometrical structures and relative stability of (SiS₂) _n (n=1–6) silicon–sulfur clusters are explored by means of density functional theory quantum chemical calculations. The effects of polarization functions and electron correlation are included in these calculations. The electronic structures and vibrational spectra of the most stable geometrical structures of (SiS₂) _n are analyzed by the same method. As a result, the regularity of the (SiS₂) _n cluster growth is obtained, and the calculation may used for predicting the formation mechanism of the (SiS₂) _n cluster. Received: 17 November 1999 / Accepted: 3 November 2000 / Published online: 3 May 2001     

Ab‐initio‐Berechnung des Tetracarbonatoscandat‐Ions in Na5[Sc(CO3)4] · 2 H2O. Einkristallstrukturbestimmung,Schwingungsspektren und thermischer Abbau

Ab Initio Calculation of the Tetracarbonatoscandate‐Ion in Na₅[Sc(CO₃)₄] · 2 H₂O. Single Crystal Structure Determination, Vibrational Spectra, and Thermal Decomposition Normal modes of the tetracarbonatoscandate‐ion, [Sc(CO₃)₄]^5–, were determined by ab initio calculations and were compared with experimental data of Infrared‐ and Raman‐spectra of the compound Na₅[Sc(CO₃)₄] · 2 H₂O. A necessary redetermination of the structure with single crystal x‐ray diffraction data (tetragonal, P42₁c (Nr. 114), Z = 2, a = 746,37(4) pm, c = 1157,0(2) pm, V_EZ = 644,5(1) 10⁶ pm³) allows the discussion of existing hydrogen bonds. Determination of the thermal behaviour indicates a two‐stage decomposition reaction, but no corresponding intermediate could be isolated.     

Anomalous non-coincidence effects in liquids: separation of attraction and repulsion contributions

A method enabling one to separate the contributions of repulsion and attraction forces resulting in frequency non-coincidences in liquids is presented.     

Carbon nanotube bundles and thin layers probed by micro-Raman spectroscopy

Raman spectra of single-wall carbon nanotubes (CNTs) either in the form of micrometer sized bundles or thin layers prepared by dilution and sonication of powders have been compared. We have been able to collect the Raman spectrum of nanotube bundles that are not in touch with the substrate, and therefore not affected by interactions with the substrate surface. This spectrum resulted to be similar to that of the precursor nanotube powders, whereas relevant changes in the Raman spectrum are detected when the diluted powders form very thin layers on either metallic or insulating surfaces, as probed by confocal microraman imaging on well defined areas of the CNTs layers. In the case of thin layers, the intensity of the Raman D band, detected between 1 320 and 1 340 cm^-1 and ascribed to disorder effects, is strongly enhanced. This enhancement occurs independently on the kind of substrate. Received 2 September 2002 Published online 4 February 2003 RID="a" ID="a"e-mail: sangalet@dmf.bs.unicatt.it     

Effective Hamiltonian approach to doubly degenerate electronic states

Effective vibronic Hamiltonian models are built for E ⊗e Jahn-Teller systems and analytical solutions are obtained through Lie algebraic methods. Although approximate, we show that these models allow in particular to recover the possible ground state crossover when quadratic couplings are present. The equivalence of E ⊗e and G' ⊗e vibronic systems in cubic symmetry is precisely established through a particular realization of the electronic operators for an orbital quadruplet. We show how this equivalence is broken by a rovibronic interaction which, for a G' ⊗e system, still gives an exactly solvable model.     

CO adsorption on epitaxially grown Pt layers on Ru(0 0 0 1)

The adsorption of CO on epitaxially grown Pt films of variable thickness has been studied using infrared-absorption spectroscopy, scanning tunnelling microscopy and thermal desorption spectroscopy. Depending on the number of pseudomorphic Pt layers (N_Pt = 1-4) the internal and external CO stretching modes (ν_C-O and ν_Pt-CO, respectively) display characteristic frequency shifts due to the vanishing influence of the underlying Ru(0 0 0 1) substrate and Pt/Ru interface. For thicker layers (N_Pt ? 5) when this influence has become negligible, the compressive stress within the Pt film is gradually relieved, leading to a dislocation network. The structural heterogeneity during the ongoing relaxation process of the Pt film is reflected in the ν_C-O line shape; no line broadening is observed for either pseudomorphic or very thick films (N_Pt ? 15). For N_Pt ? 3 the adsorption of CO on Pt/Ru(0 0 0 1) films closely resembles CO on Pt(1 1 1), with residual deviations in line position and desorption temperatures gradually converging to zero.