The nu(2), nu(4) + nu(5), nu(6) + nu(9), and nu(8) Band System in 1,1,1-Trifluoroethane

High-resolution FTIR spectra of 1,1,1-trifluoroethane (HFC-143a) have been recorded in the region from 1370 to 1470 cm(-1) with an unapodized resolution of 0.0016 cm(-1) at room temperature and of 0.004 cm(-1) at 183 and 100 K. The two main infrared active bands of A(1) symmetry have been shown to be nu(2) at 1407.5 cm(-1) and nu(4) + nu(5) at 1440.5 cm(-1). With the aid of Raman spectra, the two infrared inactive bands of E symmetry in this spectra region have been shown to be nu(8) at 1457.5 cm(-1) and nu(6) + nu(9) at 1446.2 cm(-1). The nu(2) band was analyzed as an isolated band, whereas the nu(4) + nu(5) band was analyzed as part of the triad nu(4) + nu(5), nu(6) + nu(9), and nu(8). Copyright 2000 Academic Press.     

End Effects for Anti-Plane Shear Deformations of Periodically Laminated STrips with Imperfect Bonding

The axial decay of Saint-Venant end effects is investigated for anti-plane shear deformations of semi-infinite generally laminated anisotropic strips. Imperfect bonding conditions are imposed at the interfaces. The analytical approach, using a displacement field which decays exponentially in the axial direction, gives rise to a transcendental equation for the real eigenvalues. The decay rate for the stresses is given in terms of the smallest positive eigenvalue. Laminated strips with periodic layout are then considered. In the presence of imperfect bonding, the effective shear elastic moduli, computed through a homogenization method, depend on the total number of slipping interfaces in the laminate. Numerical examples confirm that the decay lengths computed with effective shear moduli represent the asymptotic values (for an increasing number of layers) for those of periodically laminated strips. This revised version was published online in July 2006 with corrections to the Cover Date.     

The stretching fundamental bands ν1, ν2 and ν4 of HSiD3

The ν₁(A₁), Si-H stretching, ν₂(A₁) and ν₄(E), Si-D stretchings, fundamental bands of HSiD₃ have been recorded at an effective resolution of ca. 0.003 cm⁻¹ between 2080 and 2280 cm⁻¹ and between 1480 and 1720 cm⁻¹, respectively. Ro-vibrational transitions of the H²⁸SiD₃ isotopologue have been assigned in the two spectral ranges, about 700 belonging to ν₁, with J′ up to 25 and K up to 21, and about 1600 to the ν₂/ν₄ dyad, with J′ up to 24 and K′ up to 19. The spectra of all the bands evidence the existence of several perturbations. The transitions of ν₁ have been analyzed either neglecting or including in the model A₁/E Coriolis-type interactions with nearby dark states. The υ₂ = 1 and υ₄ = 1 states have been fitted simultaneously taking into account several ro-vibrational interactions between them and, in addition, with the υ₅ = 2, l = 0 component, and with few other close dark states. The standard deviation of the fit for both ν₁ and the ν₂/ν₄ dyad is, however, more than one order of magnitude larger than the estimated experimental precision and is independent on the adopted model.     

The high-resolution infrared spectrum of ethane-1,1,1-D3 rovibration analyses of the pseudoperpendicular A1A2ν9 + ν10 band and the parallel ν3 + ν4 and ν5 bands

A complete vibration-rotation analysis was made of the A₁A₂ combination band ν₉ + ν₁₀ of CH₃CD₃ at 2582 cm^?1. This band exhibits pseudoperpendicular structure due to the large effective Coriolis interaction constant (ζ ≈ 0.7), which couples the almost degenerate A₁ and A₂ vibrational components for all nonzero values of the rotational quantum number K, and gives a subband Q-branch spacing of 2.5 cm^?1. The location of the band center is assisted through an interruption of the perpendicular-like structure, since both K = 0 Q branches are forbidden by the vibrational and rotational selection rules. The conventional A₁ parallel bands ν₃ + ν₄ at 2507 cm^?1 and ν₅ (CC stretch) at 905 cm^?1 were also analyzed. For ν₅, a combination of numerical analysis and band contour simulation was used to determine a set of upper-state rotation parameters. Combination of the present results with previous data for ν₉ and 2ν₃ permits rotational parameters to be derived for the ν₄ and ν₁₀ fundamentals of CH₃CD₃. Neither of these fundamentals are amenable to straightforward analysis, both being very weak in the infrared and overlaid by the intense ν₁₁ fundamental.     

Stability of slender beams and frames resting on 2D elastic half-space

Making use of a mixed variational formulation based on the Green function of the substrate, which assumes as independent fields the structure displacements and the contact pressure, a simple and efficient finite element-boundary integral equation coupling method is derived and applied to the stability analysis of beams and frames resting on an elastic half-plane. Slender Euler–Bernoulli beams with different combinations of end constraints are considered. The examples illustrate the convergence to the existing exact solutions and provide new estimates of the buckling loads for different boundary conditions. Finally, nonlinear incremental analyses of rectangular pipes with compressed columns and free or pinned foundation ends are performed, showing that pipes stiffer than the soil may exhibit snap-through instability.     

Methyl cianide: Spectroscopic studies of isotopically substituted species,and the harmonic potential function

The infrared gas-phase spectra of CH₃CN, ¹³CH₃CN, CH₃¹³CN, CH₃C¹⁵N, CD₃CN, and CD₃¹³CN have been studied in detail, in order to determine accurately the fundamental vibration frequency displacements on heavy isotopic substitution. A number of important Fermi resonances have been identified, and treated quantitatively. The unperturbed fundamental frequencies and heavy isotopic displacements form a self-consistent set of data, which, together with Coriolis zeta and centrifugal distortion constants, enable the harmonic potential function of methyl cyanide to be determined with only one constraint. A comparison between the latter and results from an ab initio calculation reveals disagreement in the values of two interaction constants, which seem well outside our experimental error. Infrared frequencies in crystalline films of CD₃CN and CD₃¹³CN at 78 K are also reported.     

Dynamic identification of beam axial loads using one flexural mode shape

In the last decades, various methods have been proposed for the experimental evaluation of tensile forces acting in tie-beams of arches and vaults. Moreover, static and dynamic approaches have been formulated to evaluate critical compressive axial forces and flexural stiffness of end constraints. Adopting Euler–Bernoulli beam model, this paper shows that, if bending stiffness and mass per unit length of a beam with constant cross-section are known, the axial force and the flexural stiffness of the end constraints can be deduced by one vibration frequency and three components of the corresponding mode shape. Finally, data conditions are given to assess a physically admissible identification of the unknown parameters.     

The emprical general harmonic force field of ethane

A total of 175 spectroscopic data, accumulated from 10 isotopic species of ethane, are used to define all 22 parameters of the harmonic potential function within narrow limits. Before calculation, numerous Fermi resonances have been identified and quantified through infrared and Raman spectroscopic studies of CH₃CD₃ and its ¹³C isotopic species. This is an essential prerequisite to such an investigation, without which a self-consistent empirical data set cannot be achieved from which to determine physically meaningful force constants. Comparison of the empirical force constants with those predicted by scaled ab initio calculations shows an excellent degree of correspondence in all force constants, and confirms that both approaches can lead to essentially identical results. Calculated values of spectroscopic data of reliable quality are listed. These should be of value to future spectroscopic investigation of isotopic ethanes and for resolving the many resonance perturbations which are present.     

Stereochemical investigation on the construction of poly-functionalized bicyclo[3.3.1]nonenones by successive Michael reactions of 2-cyclohexenones

A method for the practical construction of poly-functionalized bicyclo[3.3.1]nonenones by successive Michael reactions of cyclohexenones with acrylates using K2CO3 and TBAB (n-Bu4N+ Br-) was developed. The construction could be carried out in both stepwise and one-pot reactions with similar tendencies in regioselectivity. The alpha-regioselectivity in the intramolecular Michael reaction agreed with that stereoelectronically expected in intermolecular reactions based upon consideration of the HOMO orbital profile of the enolate I, the precursor to ring-closure, although the reaction site was trisubstituted and prone to steric hindrance in most of the examples presented. For the acetoxymethylacrylates substituted at either the alpha or gamma position, steric hindrance of the substituents (R2 and R3) served as a controlling factor to induce high regiocontrol. Facial selection in the protonation of enolate II, formed upon ring-closure, was also affected by these substituents. In both the intramolecular Michael reaction and the protonation of enolate II, the ammonium counter cation played an important role.