Spectral diffusion in the tunneling spectra of ligand-stabilized undecagold clusters

We report diffusion in the tunneling spectra of isolated, ligand-stabilized undecagold (Au11) clusters immobilized by attachment to alpha,omega-alkanedithiolate tethers inserted into alkanethiolate self-assembled monolayers. We use scanning tunneling microscopy and spectroscopy at cryogenic (UHV, 4 K) conditions to measure these clusters' conductance with complete control of their chemical and physical environment; additionally, thermal broadening of their electronic states as well as their mobility is minimized. At low temperature, the Au11 clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects. Surprisingly, chemically identical and even single particles produced different families of tunneling spectra, comparable to previous results for heterogeneous distributions of particles. We hypothesize that, while these particles are chemically attached to the surface of the SAM for measurement, these assemblies may still be sufficiently dynamic to affect their transport properties significantly.     

Studies on terpenoids and steroids—2 : Structures of two new tri- and tetra-oxygenated D:A-friedo-oleanan triterpenes from kokoona zeylanica

The two D:A-friedo-oleanane triterpenes kokzeylanol and kokzeylanonol isolated from the inner bark of Kokoona zeylanica have been characterized as 6β,27-dihydroxy-D:A -friedo-olean-3-one and 6β,27-dihydroxy-D:A-friedo-olean-3,21-dione, respectively, by the deoxygenation of their 27-acetoxy derivatives using lithium-ethylenediamine reduction coupled with spectroscopic and irradiation methods. Kokzeylanonol represents the first tetra-oxygenated D:A-friedo-oleanane triterpene obtained from a nautral source. Significance of some of these D:A-friedo-oleananes in the biosynthesis of quinonoid triterpenes in Celastraceae is discussed.     

Asymptotic Energy Expansion for Rational Power Polynomial Potentials

Asymptotic energy expansion method is extended for polynomial potentials having rational powers. New types of recurrence relations are derived for the potentials of the form V(x)= x2n/m+b1xn1/m1+b2x n2/m2+ …+ bNxnN/mN where n, m, n1, m1, . . . , nN, mN are positive integers while coefficients bk∈C. As in the case of even degree polynomial potentials with integer powers, all the integrals in the expansion can be evaluated analytically in terms of Γ functions. With the help of two examples, we demonstrate the usefulness of these expansions in getting analytic insight into the quantum systems having rational power polynomial potentials.     

Ion association and hydration in aqueous solutions of copper(II) sulfate from 5 to 65 degrees C by dielectric spectroscopy

Aqueous solutions of copper(II) sulfate have been studied by dielectric relaxation spectroscopy (DRS) over a wide range of frequencies (0.2 less, similar nu/GHz < or = 89), concentrations (0.02 < or = m/mol kg(-1) less, similar 1.4), and temperatures (5 < or = t/ degrees C < or = 65). The spectra show clear evidence for the simultaneous existence of double-solvent-separated, solvent-shared, and contact ion pairs at all temperatures, with increasing formation especially of contact ion pairs with increasing temperature. The overall ion association constant corresponding to the equilibrium: Cu2+(aq) + SO4(2-)(aq) right harpoon over left harpoon CuSO4(0)(aq) was found to be in excellent agreement with literature data over the investigated temperature range. However, the precision of the spectra and other difficulties did not allow a thermodynamic analysis of the formation of the individual ion-pair types. Effective hydration numbers derived from the DRS spectra were high but consistent with simulation and diffraction data from the literature. They indicate that both ions influence solvent water molecules beyond the first hydration sphere. The implications of the present findings for previous observations on copper sulfate solutions are briefly discussed.     

Development of an algorithm for automatic detection and rating of squeak and rattle events

A new algorithm for automatic detection and rating of squeak and rattle (S&R) events was developed. The algorithm utilizes the perceived transient loudness (PTL) that approximates the human perception of a transient noise. At first, instantaneous specific loudness time histories are calculated over 1-24 bark range by applying the analytic wavelet transform and Zwicker loudness transform to the recorded noise. Transient specific loudness time histories are then obtained by removing estimated contributions of the background noise from instantaneous specific loudness time histories. These transient specific loudness time histories are summed to obtain the transient loudness time history. Finally, the PTL time history is obtained by applying Glasberg and Moore temporal integration to the transient loudness time history. Detection of S&R events utilizes the PTL time history obtained by summing only 18-24 barks components to take advantage of high signal-to-noise ratio in the high frequency range. A S&R event is identified when the value of the PTL time history exceeds the detection threshold pre-determined by a jury test. The maximum value of the PTL time history is used for rating of S&R events. Another jury test showed that the method performs much better if the PTL time history obtained by summing all frequency components is used. Therefore, rating of S&R events utilizes this modified PTL time history. Two additional jury tests were conducted to validate the developed detection and rating methods. The algorithm developed in this work will enable automatic detection and rating of S&R events with good accuracy and minimum possibility of false alarm.     

The intersection seam between the 11A′ and 21A′ states of ozone

The intersection seam between the two lowest ¹A^′ states of ozone has been determined. The potential energy surfaces and the seam are calculated and discussed in perimetric coordinates which exhibit the full three-dimensional symmetry. The seam is shown to form a closed curve which crosses the C _{2 v} -restricted coordinate planes at six points. Three of these correspond to the previously determined intersection, the starting point of the present search. The other three correspond to highly repulsive regions on the potential energy surface where two atoms approach each other to within two-thirds of the O₂ bond length. At the former three points both states have ¹ A ₁ symmetry, but at the latter three points one state has ¹ A ₁ symmetry whereas the other has ¹ B ₂ symmetry. Consequently, there exist three additional branches of the intersection seam between these two states. Each of these branches lies entirely in one C _{2 v} -restricted coordinate plane and connects to the previously discussed C _s -seam at one point. The existence of a further intersection seam is established. A novel method for determining intersection points is described. Received: 10 January 1996 / Accepted: 2 January 1997     

High resolution 1H NMR structural studies of sucrose octaacetate in supercritical carbon dioxide

High pressure (HP), high resolution (HR), proton nuclear magnetic resonance (1H NMR) spectroscopy has been utilized for the first time to investigate the solution structure of a carbohydrate based system, sucrose octaacetate (SOA), in supercritical CO2. The studies indicate that the average solution state conformation of the alpha-D-Glucopyranosyl ring of SOA in scCO2 medium is consistent with the 4C1 chair form, while the beta-D-fructofuranosyl ring adopts an envelope conformation. The investigations also suggest that scCO2 is a promising medium to study the solution structure and conformation of acetylated sugar systems. Spectral manifestations of a specific interaction between the acetate methyl protons and CO2 molecules are also presented.     

Assignment of the 13C nuclear magnetic resonance spectra of three 27-hydroxyfriedelanes

¹³C NMR spectra of 27-hydroxyfriedelane, kokoonol (27-hydroxyfriedelan-3-one) and kokoononol (27-hydroxyfriedelan-3,21-dione) have been recorded and signals assigned using the off-resonance decoupling, inversion recovery and lanthanide induced shift techniques.