No abstract

The synthesis, structure, and acid function of solid phosphoric acid (SPA) catalyst were studied in detail. 31P and 29Si MAS NMR and X-ray powder diffraction identified the following crystalline silicon phosphate phases in SPA:  Si5O(PO4)6, hexagonal-SiP2O7, Si(HPO4)2·H2O, and SiHP3O10. The acidity of SPA is due to a liquid or glassy solution of phosphoric acid oligomers supported on the silicon phosphate phases. 15N MAS NMR of adsorbed pyridine-15 N and 13C MAS NMR of adsorbed acetone-2-13 C showed Brønsted acid sites and no Lewis acid sites. 1H→15N→31P and 1H→13C→31P double cross polarization MAS NMR of the probe molecules provided a rare opportunity to use NMR to unambiguously localize chemisorption sites; the probe molecules are complexed to phosphoric acid and pyrophosphoric acid but not to the silicon phosphate phases. In situ NMR of the oligomerization of propene on SPA suggests that propene quantitatively reacts with phosphoric acid and its oligomers to form isopropyl phosphate, and formation of this very stable intermediate accounts for the lower olefin oligomerization activity of SPA relative to acidic zeolites. Theoretical calculations including geometries at B3LYP/6-311+G(d,p) and chemical shifts at GIAO-MP2/tzp/dz were used to model complexation of acetone or propene to SPA, and these support our conclusions.

Subduction zone earthquakes have not been taken into special consideration in most previous probabilistic seismic hazard analyses (PSHA) in Taiwan. However, they may be critical to properly analyze the earthquake hazard in metropolitan Taipei, so they need to be studied. Strong-motion data from subduction zone earthquakes, of both interface and intraslab types, obtained by the TSMIP and SMART1 arrays in northeastern Taiwan, are used to establish the attenuation equations for peak ground acceleration (PGA) and response spectral acceleration (SA). The resultant PGA and SA attenuation equations include two site classes and two earthquake source types. The ground-motion values predicted by these attenuation equations are higher than those obtained from the crustal earthquake attenuation equations previously used in Taiwan but are lower than those predicted by the attenuation equations for worldwide subduction zone earthquakes.

In this study, we quantify the reduction in the standard deviation for empirical ground-motion prediction models by removing ergodic assumption. We partition the modeling error (residual) into five components, three of which represent the repeatable source-location-specific, site-specific, and path-specific deviations from the population mean. A variance estimation procedure of these error components is developed for use with a set of recordings from earthquakes not heavily clustered in space. With most source locations and propagation paths sampled only once, we opt to exploit the spatial correlation of residuals to estimate the variances associated with the path-specific and the source-location-specific deviations. The estimation procedure is applied to ground-motion amplitudes from 64 shallow earthquakes in Taiwan recorded at 285 sites with at least 10 recordings per site. The estimated variance components are used to quantify the reduction in aleatory variability that can be used in hazard analysis for a single site and for a single path. For peak ground acceleration and spectral accelerations at periods of 0.1, 0.3, 0.5, 1.0, and 3.0 s, we find that the singlesite standard deviations are 9%-14% smaller than the total standard deviation, whereas the single-path standard deviations are 39%-47% smaller.

A combined experimental and theoretical study of the polar and azimuthal dependence of the molecular frame photoelectron angular distributions (MFPADs) for inner-valence-shell photoionization of the O2 molecule into the O2+(B 2Σg−,3 2Πu,c 4Σu−) states is reported. The measured MFPADs, for each orientation of the molecular axis with respect to the linear polarization of the synchrotron radiation, are derived from the spatial analysis of the (VO+,Ve,P) vector correlation, where the nascent ion and electron velocity vectors VO+ and Ve are determined for each dissociative photoionization (DPI) event using imaging and time of flight resolved coincidence technique as described in the companion paper of this series [J. Chem. Phys. 114, 6605 (2001)]. Expressed in the general form of four FLN(θe) functions which contain all the dynamical information about the photoionization processes, they are compared with the MFPADs computed using the multichannel Schwinger configuration interaction method. A very satisfactory agreement is found. When the lifetime of the O2+ ionic states is a significant fraction of the rotational period, the rotational motion of the molecule is included in the quantal derivation of the MFPADs. Measured MFPADs are also reported for the additional DPI process identified in Paper I, and for DPI involving the excitation of the neutral (3 2Πu,4sσg) Rydberg state.