Platinum-Catalyzed Asymmetric Hydrogenation: Spectroscopic Evidence for an O-H-O Hydrogen-Bond Interaction between Substrate and Modifier

The mighty cinchonidine: A diastereomeric surface complex in the asymmetric hydrogenation of ketopantolactone on chirally modified Pt is monitored by in?situ ATR-IR spectroscopy, in combination with modulation excitation spectroscopy and phase-sensitive detection. Cinchonidine bound to the surface with its quinoline ring is shown to induce the chiral environment through a C9?O???H???O?C interaction.     

Coherent Raman and Infrared Studies of Sulfur Trioxide

High-resolution (0.001 cm⁻¹) coherent anti-Stokes Raman scattering (CARS) was used to observe the Q-branch structure of the IR-inactive ν₁ symmetric stretching mode of ³²S¹⁶O₃ and its various ¹⁸O isotopomers. The ν₁ spectrum of ³²S¹⁶O₃ reveals two intense Q-branches in the region 1065–1067 cm⁻¹, with surprisingly complex vibrational–rotational structure not resolved in earlier studies. Efforts to simulate this with a simple Fermi-resonance model involving ν₁ and 2ν₄ states do not reproduce the spectral detail, nor do they yield reasonable spectroscopic parameters. A more subtle combination of Fermi resonance and indirect Coriolis interactions with nearby states, 2ν₄(1=0, ±2), ν₂+ν₄(1=±1), 2ν₂(1=0), is suspected and a determination of the location of these coupled states by high-resolution infrared measurements is under way. At medium resolution (0.125 cm⁻¹), the infrared spectra reveal Q-branch features from which approximate band origins are estimated for the ν₂, ν₃, and ν₄ fundamental modes of ³²S¹⁸O₃, ³²S¹⁸O₂¹⁶O, and ³²S¹⁸O¹⁶O₂. These and literature data for ³²S¹⁶O₃ are used to calculate force constants for SO₃ and a comparison is made with similar values for SO₂ and SO. The frequencies and force constants are in excellent agreement with those obtained by Martin in a recent ab initio calculation.     

High-Resolution Infrared Spectra of the ν2, ν3, ν4, and 2ν3 Bands of SO3

New measurements are reported for the infrared spectrum of sulfur trioxide, ³²S¹⁶O₃, with resolutions ranging from 0.0015 cm⁻¹ to 0.0025 cm⁻¹. Rovibrational constants have been measured for the fundamentals ν₂, ν₃, and ν₄ and the overtone band 2ν₃. Comparisons are made with the earlier high-resolution measurements on SO₃, and the high correlation among some of the constants related to the Coriolis coupling of the ν₂ and ν₄ levels is discussed in order to understand the areas of disagreement with the earlier work. Splittings of some of the levels are observed and the splitting constant for K=3 of the ground state is determined for the first time. Other observed splittings include the K=1 levels of 2ν₃ (l=2), the K=2 levels of ν₃ and ν₄, and the K=3 levels of ν₂. The analysis shows that there are level crossings between the l=0 and l=2 states of 2ν₃ that allow one to determine the separation of the subband centers for these two states even though access to the l=0 state from the ground state is electric-dipole forbidden. This is a generalized phenomenon that should be found for many other molecules with the same symmetry. The l-type resonance constant, q₃, that causes the splitting of the l₃=±1, k=±1 levels of ν₃ also couples the l₃=0 and 2 states of 2ν₃.     

Colloidal Silica Rods: Material Properties and Fluorescent Labeling

In this paper, the characterization and fluorescent labeling of silica rods are reported. These rods are synthesized following a recently reported method. Material properties of the silica rods measured with NMR, elemental analysis, TGA, and porosimetry are compared with those of well‐established Stöber silica spheres. Additionally, silica rods are made suitable for quantitative real‐space studies by confocal microscopy. Several methods of fluorescent labeling to prepare rods with different fluorescent patterning, ranging from uniform fluorescence levels to gradients from one rod‐end to the other, and even patterns of several colors are presented and discussed.     

Commensurable charge-density waves in a random potential

We study commensurable charge-density wave systems in the presence of random impurities. The results of the microscopic theory, especially the contributions of second order in the impurity fields, are briefly discussed. The lifetime of the excitations is calculated, as well as the response of a soliton to an external field.     

Randomized Decisions in Chance-Constrained Programming

Bhattacharyya and Mukherjee have both considered a particular joint randomized decision problem in chance-constrained programming. This paper shows a general approach for solving a large class of similar problems.     

Über methylirte Phloroglucine

Ohne Zusammenfassung     

Über Tetramethylphloroglucin

Ohne Zusammenfassung     

Unprecedented formation of metastable monoclinic BaCO3 nanoparticles

Barium carbonate nanoparticles (50-100 nm) were prepared by flame spray pyrolysis. The rapid quenching during the preparation process resulted in the unprecedented formation of pure monoclinic BaCO₃. The as-prepared materials were characterized by electron microscopy, X-ray diffraction as well as by thermogravimetric and differential scanning calorimetric analyses. At ambient conditions the metastable monoclinic phase transformed easily into the thermodynamically stable orthorhombic BaCO₃ (witherite) within a few days.