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The effect of phase transfer agent in the dynamics of monolayer protected gold nanoparticles has been investigated by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies. The experiments were performed with octadecane thiol and dodecane thiol protected gold nanoparticles. The materials prepared were characterized by UV-Visible spectroscopy, transmission electron microscopy and IR spectroscopy. Repeated purification of the monolayer protected gold clusters made the alkyl chains defect-free. Such effects are reflected in the infrared spectra. Interdigitation of the monolayers that followed the purification leads to alkyl chains with limited mobility. This was reflected in 13C and 1H NMR line-widths. The NMR measurements indicate that the removal of phase transfer agent affects the dynamics of isolated clusters and those with interdigitated monolayers in different ways. � Indian Academy of Sciences.

We have prepared semiconducting carbon nanoparticle polyimide composite thin film with spatially distributed localized energy states exhibiting three-dimensional variable range hopping electron transport. Applied strain (compression or extensional) introduces proportional variations in the spacing between these energy states, as demonstrated in the linear variation of measured electrical resistance. The electromechanical sensitivity is the same in both deformation modes due to this underlying operating mechanism, enabling quantitative measurement of torsional deformations also. Electrical responses across all deformation modes remained in phase with applied strain indicating negligible hysteresis and an ability to operate over a wide strain ranges up to 40 000 microstrains. � 2008 American Institute of Physics.

We report electric quadrupole (E2) and magnetic dipole (M1) transition amplitudes of the first few low-lying states of quadruply ionized vanadium (V4+), which are important in various experimental applications and astrophysics. To our knowledge, most of these presented results are determined for the first time in the literature. A relativistic multireference Fock-space coupled-cluster theory with single (S), double (D), and partial triple (T) excitations is employed to compute the forbidden transition probabilities and lifetimes of the low-lying states in V4+. Estimations of different correlation effects arising through the above formalism have been highlighted by investigating core and valence electron excitations. A long lifetime is found for the first excited 3d D 5 2 2 state, which suggests that V4+ may be one of the useful candidates for many important studies. � 2007 The American Physical Society.

A modified semiclassical exchange potential (MSCEP) has been used in the distorted wave Born approximation (DWBA) to calculate the triple differential cross section of Xe(4d) in the coplanar asymmetric geometry at intermediate energy. The scattered and ejected electron energies are fixed at 1000 eV and 100 eV, respectively. Calculations have been carried out for the ejected electron angles of 2� and 8�. Agreement between the present calculations and experiment is better compared to that of earlier calculations using the corrected form of the local exchange potential of Furness and McCarthy (1973 J. Phys. B: At. Mol. Opt. Phys. 6 2280). � 2006 IOP Publishing Ltd.

The calculation of rovibrational transition energies and intensities is often hampered by the fact that vibrational states are strongly coupled by Coriolis terms. Because it invalidates the use of perturbation theory for the purpose of decoupling these states, the coupling makes it difficult to analyze spectra and to extract information from them. One either ignores the problem and hopes that the effect of the coupling is minimal or one is forced to diagonalize effective rovibrational matrices (rather than diagonalizing effective rotational matrices). In this paper we apply a procedure, based on a quantum mechanical canonical transformation for deriving decoupled effective rotational Hamiltonians. In previous papers we have used this technique to compute energy levels. In this paper we show that it can also be applied to determine intensities. The ideas are applied to the ethylene molecule. ? 2005 American Institute of Physics.

Ultrafast pump-probe spectroscopy of phenylene-based π-conjugated polymers give low and high energy photoinduced absorptions (PAs) to final states with very different relaxation behavior. While the low energy two-photon state that is reached in PA relaxes to the optical exciton in ultrafast times, the higher energy two-photon state violates the Vavilov–Kasha rule and instead of relaxing to the optical exciton undergoes interchain dissociation to a polaron pair state. We have calculated the excited state absorptions of long oligomers of poly-paraphenylene and poly-paraphenylenevinylene within a rigid band correlated electron Hamiltonian, using the complete π-electron basis and the powerful multi-reference singles and double configuration interaction technique. Our calculated PA spectra well reproduce the experimental PA. We further show that there exists a fundamental difference in the natures of the wavefunctions of the final states that are reached in low and high energy PA, and the difference originates from the existence of multiple kinds of bands in phenylene-based systems within one-electron theory. We speculate that the violation of the Vavilov–Kasha rule and charge separation into polaron pairs upon excitation to the high energy two-photon state is a consequence of its specific electronic structure, and discuss an earlier work on wavelength dependent photoconductivity of poly-paraphenylenevinylene to support this conjecture., © Elsevier

The absolute photoionization cross sections of doubly ionized silicon in the ground state as a function of photon energy in the region of 2p threshold (95eV-170eV) was presented. The cross sectional values contained a small contribution from metastable Si2+ that did not exceed 3%. The relativistic random-phase approximation (RRPA) was used to calculate the 2p photoionization continuum cross sections and agreed well with the corresponding measurements. It was found that the satellite transitions play an important role in the photoionization of Si2+.

The standard exchange current densities pertaining to electron transfer processes at electrodes are employed to estimate chemical hardness of various metals. This is accomplished by deriving a new parametric relation for hardness in terms of the work function and surface potential of electrons. Hydrogen evolution and ferric/ferrous redox reactions are considered as examples to extract chemical hardness from electrode kinetic data. The surface potential is calculated for a large number of metals using phenomenological thermodynamic considerations. The significance of the methodology is also illustrated by calculating the potential of zero charge of metal/solution interfaces, thus demonstrating that equilibrium as well as kinetic studies in electrochemistry are capable of yielding the hardness of metals.

Photoionization cross sections and asymmetry $(\ensuremath{\beta})$ parameters for Kr $3s,$ $3p,$ and $3d$ subshells have been measured and calculated in the 300--1300-eV photon energy range. Good agreement between experiment and theory is found for both cross-section branching ratios and $\ensuremath{\beta}$ parameters. Interchannel coupling among the channels arising from $3s,$ $3p,$ and $3d$ subshells is found to be necessary for quantitative accuracy of the theory. This shows that the interchannel coupling phenomenology far above threshold, found previously for outer shells of Ne and Ar, is also operative for inner atomic shells.

The microenvironmental dependence of excited state prototropism of 1-naphthol and the corresponding changes in its fluorescence emission is utilized to monitor the acyl chain melting phase transition behavior of liposome membrane made from human erythrocyte lipids. A sharp increase in the ratio of neutral/anionic form fluorescence intensity is noticed at the phase transition temperature (19°C). This provides a convenient method for obtaining phase transition temperature in lipid membranes. The membrane modifying effect of cholesterol on the erythrocyte liposome is successfully sensed by 1-naphthol fluorescence.

In the resonant tunneling devices made of mixed gap materials such as AlAs/GaAs/AlAs, the quantum well for the � valley resided in the GaAs layer and those of the X valley in the AlAs layer. There are resonance energy levels in each of these valleys. Our calculation of I-V characteristics suggests a new possibility of a considerable increase in the peak-to-valley current ratio if one resonance level of the � valley aligns with that in the second AlAs X valley. For one choice of empirical tight-binding band structures of GaAs and AlAs, the resonant level alignment increases the peak-to-valley ratio by two orders of magnitude. We further show that the predicted resonance levels are exceedingly sensitive to the barrier thickness and the quality of underlying band structures. ? 1998 American Institute of Physics.

We have analysed the bound states in a primary one-dimensional δ-function potential perturbed by a δ-function potential at a different point, in terms of the poles of the scattering amplitude. The singularities of the pole positions correspond to the crossing of the poles, and allow us to determine the domains of convergence of the perturbation series. We have obtained the first few terms in the perturbation series for the two bound states., © Elsevier

Single phase Ba- free Sr-based YSr2Cu3-xMxO7+� (M = Mo, W and Re) compounds have been stabilized by chemical doping. Superconductivity is observed for these phases in the range 30-45 K. X-ray diffraction studies suggest a relatively small orthorhombicity compared to Ba-analogue. X-ray photoelectron spectroscopic investigations reveal that the stabilizing cations are in the hexavalent state. The observation of the higher oxidation state of M-ions accounts for the excess oxygen content in these phases which is in accordence with the diffraction results.

We report the directional magnetic susceptibilities on single crystals of NdBa 2 Cu 3 O 7− δ . Crystal field (CF) analysis considering orthorhombic symmetry at the Nd 3+ site has been performed and a best set of CF parameters have been obtained. The energy levels obtained from the present fit are in good agremment with the inelastic neutron scattering spectra.

Microwave cavity perturbation technique has been employed for the study of photo conductive transients in semiconductors. A new approach of measuring the quality factor of the microwave cavity using cavity perturbation technique (reported in Rev. Sci. Instrum. 65 (1994) 453] is incorporated for this purpose. Measurements with this contactless technique on carrier lifetimes in various single and polysilicon and the analysis of the observed microwave transient photo conductivity decay with temperature is reported.

[No abstract available]

Results of thermoluminescence, optical absorption and fluorescence studies on thallium doped sulphates of cesium, rubidium and potassium are reported. The C band of Tl+ is observed in the 5.77–5.85 eV region. Fluorescent emissions from the 3P1.0 levels are observed by excitation into the C and A bands. Tl+ acts as an electron trap during γ-irradiation. The hole centres formed during irradiation recombine with Tl0 during heating to give thermoluminescence. The TL emission spectra and the fluorescence spectra are similar indicating that the process of emission is the same in both cases.

A systematic study of the effect of Y doping at the Ca site in the high- T c superconductor Bi2212 has been made. Starting with an off-stoichiometric composition Bi 2.1 Sr 1.93 (Ca 0.97− x Y x )Cu 2 O 8+ y (BiY2212) by power X-ray diffraction, resisti vity, AC and DC susceptibility and XPS measurements have shown the single-phase nature for all values of x . The decrease in T c observed systematically by both resistivity and AC susceptibility measurements with increasing Y concentration, and the subsequent metal-semiconductor cross-over, is explained as due to the decrease in the average valence of the copper brought about by the excess charge introduced by Y. The Cu 2p core level shows that the relative intensity of the satellite, the energy separation between main line and satellite, and the binding energy of the main line vary in a systematic way. A decrease in charge-transfer energy and an increase in the hybridisation strength is predicted for higher x with the configuration interaction model. The presence of internal strain in this superconductor makes the BVS calculation not applicable.