ALBERT

Notes: Low shear (γ(overdot)=1 s−1) and shear rate dependent (1 s−1〈γ(overdot)〈100 s−1) viscosity measurements on aqueous suspensions of rodlike FD-virus particles (length=880 nm, diameter=9 nm) below and above the overlap concentration c* =1 particle/length3 are presented. Properties like intrinsic viscosity [η], the virus concentration and shear rate dependence of η are studied in deionized ("saltfree'') suspensions and in the presence of NaCl, where the Coulomb interaction between the particles is totally screened. In the latter case, [η] is in excellent agreement with theoretical predictions [A. R. Altenberger and J. S. Dahler, Macromolecules 18, 1700 (1985); R. M. Davis and W. B. Russel, Macromolecules 20, 518 (1987)]. As a function of the virus concentration, η follows certain power laws in c. The observed exponents depend here on the applied shear rate. In the low shear region, η(c) can be described by the well known Huggins behavior. An attempt to fit the data by the popular stretched exponential form failed. The variation of η with shear rate is compared with available theories [M. Doi and S. F. Edwards, The Theory of Polymer Dynamics (Clarendon, Oxford, 1986); A. R. Altenberger and J. S. Dahler, Macromolecules 18, 1700 (1985); J. S. Dahler, S. Fesciyan, and N. Xystris, Macromolecules 16, 1673 (1983)]. A theory of Hess [Z. Naturforsch. Teil A 35, 915 (1980)] allows us to evaluate the concentration dependent values of the rotational diffusion constant Drot from the η(γ(overdot)) data which are found to be in very good agreement with the values of Drot, obtained by electric or magnetic birefringence [H. Kramer, M. Deggelmann, C. Graf, M. Hagenbüchle, C. Johner, and R. Weber, Macromolecules 25, 4325 (1992); J. F. Maguire and J. P. McTague, Phys. Rev. Lett. 45, 1891 (1980); H. Nakamura and K. Okano, Phys. Rev. Lett. 50, 186 (1983)]. For strong Coulomb interaction among the suspended viruses no adequate theory is available. Therefore, the data achieved under these conditions are interpreted in terms of the corresponding results of the non-Coulomb interacting samples.

Notes: Interaction energies of K+ and NH+4 with the model ligands methyl-propyl-ether, N-ethyl-N-methyl-acetamide, 1,2-dimethoxy-ethane, 2-methoxy-N,N-dimethyl-ethylamine, and ethyl-propionate were determined by performing ab initio SCF-LCAO-MO calculations for about 1000 complex structures. Atom pair potentials were obtained by fitting the calculated interaction energies with an analytical potential. Both the form of the analytical potential and the assignment of atoms to classes, i.e., in groups having the same atom pair potential values, were amended relative to earlier contributions. Previously determined Li+ and Na+ interaction energies were fitted into a consistent form of analytical potential and classification. The pair potentials obtained were applied for the calculation of interaction energies between the ions and 18-crown-6 and the results were compared with corresponding ab initio calculations.

Notes: Time correlation functions of the scattered light intensity are studied in aqueous solutions of charged rod-like fd-virus (L=880 nm, d=6 nm) at various ionic strengths. The short time behavior of the correlation function is dominated by the static structure factor S(q) which is also independently determined from static light scattering experiments. Comparison of correlation functions of solutions with high ionic strength (screened Coulomb interaction) and those of solutions with liquid-like nearest neighbor order (strong Coulomb interaction) shows different single particle diffusion coefficients on medium time scales at high scattering vectors, where mainly single particle properties are observed by light scattering. The single particle diffusion coefficient decreases with increasing structure peak height of the solutions. At low scattering vectors an extra slow mode component of the correlation function is observed for solutions with Coulomb interaction.

Notes: We report a new mechanism for intramolecular vibrational redistribution (IVR) in CF3CHFI which couples the CH chromophore vibrations through a strong Fermi resonance to the formal CF stretching normal mode (a heavy atom frame mode) involving the trans F-atom across the CC bond. The analysis is made possible by comparing spectroscopic results with extensive ab initio calculations of the vibrational fundamental and overtone spectra in the range extending to 12 000 cm−1. Potential energy and electric dipole moment hypersurfaces are calculated ab initio by second order Møller–Plesset perturbation theory (MP2) on a grid involving the CH stretching, two CH bending modes and one high frequency CF stretching normal mode. The potentials are scaled to obtain agreement between the experimental spectrum and the theoretical spectrum calculated by a discrete variable representation technique on this grid. Both spectra are then analyzed in terms of three-dimensional (3D) and four-dimensional (4D) effective vibrational Hamiltonians including Fermi- and Darling–Dennison-type resonances between the CH stretching mode and the CH bending modes and the CF stretching mode. The interaction between the CH modes and the CF mode is clearly visible in the experimental and calculated (4D) spectra. The effective Fermi resonance coupling constants [ksff′(similar, equals)(40±10) cm−1 and ksaf′(similar, equals)(55±10) cm−1] coupling the CH and CF mode subspaces are of about the same magnitude as the intra-CH chromophore Fermi resonances (ksaa′(similar, equals)56 cm−1 and ksbb′(similar, equals)42 cm−1, coupling CH stretching mode "s" with the two CH bending modes "a" and "b"). The chiral, pseudo-Cs symmetry breaking coupling (ksab′(similar, equals)11 cm−1) is complemented by an equally strong coupling through the CF mode (ksfb′(similar, equals)15 cm−1). It is demonstrated that low order perturbation theoretical analysis using potential constants from a polynomial expansion to represent effective coupling constants gives inadequate results with discrepancies ranging about from factors of 2–5. Time dependent population and wave packet analysis shows essentially complete IVR among the CH chromophore modes within about 100 fs, the 3D and 4D evolutions being similar up to about that time. At longer times of about 250 fs, there is substantial excitation of the CF stretching mode (with initial pure CH stretching excitation). The 4D treatment is then essential for a correct description of the dynamics. © 2000 American Institute of Physics.

Notes: The pure rotational spectrum in the far-infrared and its absolute intensity in the vibrational ground state of CHD3 and CH3D, and the integrated band strength of the N=5 CH-stretching overtone of CHD3 in the near infrared to visible were measured by high-resolution interferometric Fourier transform techniques. The far-infrared data result in permanent electric dipole moments (||μz0||=(5.69±0.14)×10−3 D for CHD3, ||μz0||=(5.57±0.10)×10−3 D for CH3D), consistent with previous experimental data. The integrated N=5 overtone cross section is found to be (0.828±0.068) fm2. The overtone data are used, together with previous data, to derive a new, nine-dimensional, isotopically invariant dipole moment function for CH4 within the chromophore model for the CH chromophore in CHD3. With this function, the experimental data can be reproduced to an averaged factor of 1.2, in the best case. In the vibrational ground state, a nine-dimensional calculation of expectation values on a new, fully anharmonic potential surface was performed using the solution of the rovibrational Schrödinger equation by diffusion quantum Monte Carlo methods. The results for the rotational constants of several isotopomers, which include significant contributions from rovibrational interactions, indicate that the equilibrium CH bond length of methane is re=108.6 pm. The calculated value for the vibrationally averaged permanent dipole moment from these nine-dimensional vibrational quantum calculations, using the dipole moment function consistent with the analysis of the overtone bands, is μz0=−(6.6±0.4)×10−3 D for CHD3 (with positive z coordinate for the H atom) and μz0=(6.8±0.5)×10−3 D for CH3D (with positive z coordinate for the D atom) in essential agreement with the far-infrared rotational intensities. The sign could be determined unambiguously by comparison with ab initio data. We predict the permanent dipole moment of several further methane isotopomers. The polarity of the CH bond in methane is C−–H+, within our simple bond dipole model, but is discussed to be a model dependent (not purely experimental) quantity.

Notes: We report analytical representations of the six-dimensional potential energy hypersurface for (HF)2, the parameters of which are closely adjusted to low energy experimental properties such as hydrogen bond dissociation energy (D0=1062 cm−1 ) and vibrational–rotational spectra in the far and mid infrared. We present a detailed analysis of properties of the hypersurface in terms of its stationary points, harmonic normal mode amplitudes, and frequencies for the Cs minimum and C2h saddle point and effective Morse parameters and anharmonic overtone vibrational structure for the hydrogen bond and the HF stretching vibrations. The comparison between experimental data and the potential energy surface is carried out by means of accurate solutions of the rotational–vibrational Schrödinger equation with quantum Monte Carlo techniques, which include anharmonic interactions between all modes for the highly flexible dimer. Two extensions of the quantum Monte Carlo technique are presented, which are based on the clamped coordinate quasiadiabatic channel method and allow for the approximate calculation of excited rotational and vibrational levels.Predictions include dissociation energies D0 for isotopomers (XF)2 with X=μ, D, T (D0=477; 1169; 1217 cm−1 ). Unusual anharmonic isotope effects predicted for the out-of-plane bending fundamental ν6 [378; 276; 295; and 358 cm−1 for (HF)2, (DF)2, (HFDF), (DFHF)] can be understood in simple terms. Centrifugal effects both for the high frequency a-axis rotation and low frequency c-axis rotation are accurately calculated for the vibrational ground state and some excited states, with a best equilibrium center of mass distance Req.ab=5.14a0 between the HF monomers. A very large anharmonic interaction constant x46≈−16 cm−1 is predicted for the hydrogen bond vibration ν4 and for out-of-plane bending ν6. This leads to assignment of our earlier experimental observation of a band at 383 cm−1 as ν6+ν4−ν4(K=1←0) at almost exactly the predicted position. The fundamental ν4 is predicted at 130±10 cm−1. A new, indirect assignment of our experimental data gives ν4≈125 cm−1. Monte Carlo calculations are presented for quasiadiabatic channels and transition states for hydrogen bond dissociation. We present a discussion of symmetry correlations for these channels and symmetry effects in predissociation by rotation, nuclear spin symmetry, and parity violation. Large effects from zero point energy on the three-dimensional quantum centrifugal barriers for rotational predissociation are found. On the basis of the new data, a much improved statistical mechanical estimate for the equilibrium 2HF=(HF)2 is obtained.

Notes: We report high level ab initio calculations (treating correlation by second order Möller–Plesset perturbation theory, MP2) of a five-dimensional normal coordinate subspace of the potential and electric dipole hypersurfaces of the Cs conformer of dideuteromethanol, CD2HOH. Accurate vibrational variational calculations are carried out using a discrete variable representation (DVR) for the five anharmonically coupled modes (three coupled CH stretching and bending modes and the OH stretching and high frequency OH bending mode). The overtone spectra of the OH chromophore are calculated and analyzed in detail with respect to their anharmonic resonance dynamics leading to short time intramolecular vibrational redistribution (IVR) via the close resonance coupling of 5νOH (5ν1) with 4νOH+νCH(4ν1+ν2), as previously observed and assigned experimentally. While the assignment of the resonance is confirmed by the ab initio calculation, a sequence of calculations including various subspaces (two-dimensional to five-dimensional) lead to the conclusion that the resonance contains important contributions from coupling to the various bending modes, not just involving the CH– and OH stretching modes. Furthermore, even in the two-dimensional subspace the effective coupling constants k1112 and k1222 characterizing the resonance are not identical with the anharmonic potential constants C1112 and C1222 in the Taylor expansion of the potential, but rather an expansion to sixth order is needed to describe the resonance quantitatively. A similar conclusion holds true with other low order perturbation expansions of the resonance coupling, involving sequences of cubic couplings to other modes. We furthermore predict important resonances between OH stretching and OH bending also involving CH bending modes, which contribute to IVR at higher levels of excitation. © 1999 American Institute of Physics.

Notes: To study the kinetics of metastable defect creation in amorphous hydrogenated silicon we introduce the Constant Degradation Method as a new experimental scheme. In contrast to conventional degradation experiments in which the incident light intensity is constant during light soaking, in this method the photoconductivity of the sample is kept constant by continuously increasing the light intensity. In this case a linear time dependence of the required light intensity and of the resulting defect density is observed experimentally. A detailed analysis of the method shows that the data obtained are in accordance with the assumption of the "bond-breaking'' model, i.e., the metastable defects are created by bimolecular recombination of localized electron-hole pairs. The observed time dependence is at variance with the stretched exponential time dependence predicted for dispersive transport models. Effects of sample heating due to high light intensities and of Fermi level shifts on the observed time dependence are also discussed.

Notes: Precise cutting of biological tissue is possible with the Er:YAG laser because of the strong absorption of radiation exhibited by water containing media at a wavelength of 2.94 μm. To achieve control of the depth of drilled channels a thorough knowledge of the channel propagation mechanism is required. The channel propagation process of pulsed erbium laser radiation in liquid water, and in gelatin with a high water content, as substitutes for biological tissue is investigated experimentally and modeled theoretically. We explain the propagation process with a hydrodynamic model, which describes the channel propagation process in terms of energy, mass, and momentum balance equations, which influence the evaporation pressure at the phase boundary. As the key feature, the theory takes into account the deformability of cold material below the zone of absorption. We show that by modeling this hydrodynamic effect with the Bernoulli equation we can explain the channel propagation velocity in water and gelatin as a function of laser intensity over three orders of magnitude with appreciable accuracy. The comparison with the experimental data suggests that the channel propagation velocity for intensities below 0.1 MW/cm2, and the threshold intensity of 12 kW/cm2 for channel propagation, are dependent on the surface tension and the liquid viscosity. At intensities above 0.1 MW/cm2, we can even predict a small difference between the propagation velocities found in these materials by considering the effect of the different elastic properties on the pressure in the propagating channel.