Effect of bending and torsional mode excitation on the reaction Cl+CH4-->HCl+CH3

A beam containing CH(4), Cl(2), and He is expanded into a vacuum chamber where CH(4) is prepared via infrared excitation in a combination band consisting of one quantum of excitation each in the bending and torsional modes (nu(2)+nu(4)). The reaction is initiated by fast Cl atoms generated by photolysis of Cl(2) at 355 nm, and the resulting CH(3) and HCl products are detected in a state-specific manner using resonance-enhanced multiphoton ionization (REMPI). By comparing the relative amplitudes of the action spectra of Cl+CH(4)(nu(2)+nu(4)) and Cl+CH(4)(nu(3)) reactions, we determine that the nu(2)+nu(4) mode-driven reaction is at least 15% as reactive as the nu(3) (antisymmetric stretch) mode-driven reaction. The REMPI spectrum of the CH(3) products shows no propensity toward the formation of umbrella bend mode excited methyl radical, CH(3)(nu(2)=1), which is in sharp distinction to the theoretical expectation based on adiabatic correlations between CH(4) and CH(3). The rotational distribution of HCl(v=1) products from the Cl+CH(4)(nu(2)+nu(4)) reaction is hotter than the corresponding distribution from the Cl+CH(4)(nu(3)) reaction, even though the total energies of the two reactions are the same within 4%. An explanation for this enhanced rotational excitation of the HCl product from the Cl+CH(4)(nu(2)+nu(4)) reaction is offered in terms of the projection of the bending motion of the CH(4) reagent onto the rotational motion of the HCl product. The angular distributions of the HCl(nu=0) products from the Cl+CH(4)(nu(2)+nu(4)) reaction are backward scattered, which is in qualitative agreement with theoretical calculation. Overall, nonadiabatic product vibrational correlation and mode specificity of the reaction indicate that either the bending mode or the torsional mode or both modes are strongly coupled to the reaction coordinate.     

An Efficient Synthesis of (±)-α-Spirovetivene and Related Compounds

A process for the synthesis of (±)-α-spirovetivene starting from I-oxo–2-carbethoxy-6, 10-dimethyl spiro[4.5]dec-6-ene(I)¹ is described. The oxo group of I was reduced by the process of Coates², and the resulting spiro ester (III) and spiro alcohol (IV) were transformed to (±)-α-spirovetivene by the process of Uijttewaal³ and by conventional methods.     

Valence electron orbitals of an oligo(p-phenylene-ethynylene)thiol on gold

This communication reports measurement of one-photon (21.2 eV) and one-color, two-photon (3.2-4.5 eV) photoemission spectra of 4,4'-bis-(phenylethynyl)benzenethiol chemisorbed on gold. Four features are observed in these spectra: two occupied, predominantly molecular levels below the Fermi level and two unoccupied, predominantly molecular levels above the Fermi level. The occupied and unoccupied bands closest to the Fermi level are assigned to delocalized pi-bands, and the other occupied and unoccupied bands, to localized pi-bands. With this assignment, the hole- and electron-injection barriers and the transport gap for those levels are deduced.     

Comparison of reversed-phase column materials for high-performance liquid chromatography of proteins

Nine reversed-phase materials with various bonded phases from different suppliers were studied for the separation of hydrophilic proteins with two solvent systems. Protein retention, resolution and recovery were not correlated with the nature of the hydrocarbonaceous ligand. Peak volumes increased with molecular weight, which led to broad, irregular peaks for the larger proteins on some columns. Four columns that performed equally well were selected for the purification of hydrophobic Sendai virus membrane proteins. In this case, more distinct differences were found between columns. Recovery of the membrane proteins strongly depended on the combination of column and solvent systems.     

Magnetic resonance imaging of pediatric spinal dysraphism

Thirty pediatric patients with spinal dysraphism were studied with magnetic resonance imaging. A variety of dysraphic anomalies were visualized, including syringohydromyelia, tethered cord, widened spinal canal, meningomyelocele, lipomyelomeningocele, lipomeningocele, intraspinal lipoma, congenital dermal sinus tract, and scoliosis. In 29 of 30 cases, MRI diagnostically visualized spinal cord and dysraphic anatomy. A combination of T1-weighted sagittal and axial imaging planes provided the most complete visualization. In specific cases, T2-weighted examinations were useful in demonstrating likely regions of inflammation bordering infected sinus tracts. MRI demonstrates a wide variety of dysraphic spinal anomalies and effectively screens children for occult spinal dysraphism.