Autoionizing rydberg states of. The Li2 molecule: Molecular constants for Li2+

Autoionizing Rydberg series of Li₂ have been observed in the two-step optical cxcitation of a supersonic lithium beam. The series limits are vibrational states of Li₂⁺. In the most probable assignment IP(Li₂) = 41236.4 ± 2.5 cm^?1 and for Li₂⁺ω_e = 263.45 ± 1.3 cm^?1; ω_eχ_e = 1.35 ± O.2 cm^?1; r_e = 3.032 ± 0.01 Å; D_e = 10807 ± 150 cm^?1.     

Megawatt VUV xenon laser employing coaxial electron-beam excitation

3 nsec laser pulses, of bandwidth 1.3 nm, are obtained from a 10 J, 600 keV coaxial diode electron-beam pumping arrangement. Uniform pumping, with a well defined cylindrical geometry, facilitates experimental investigation of the laser parameters. Gas heating limits the laser repetition rate. While mirror damage at present limits the peak power to ∽ 1 MW, higher powers seem available. The addition of helium results in a drastic reduction of peak molecular xenon fluorescence.     

Evolution of the dUTPase gene of mammalian and avian herpesviruses

Sequences of dUTPases encoded by Alpha- and Gammaherpesviruses resemble other dUTPases in their possession of five conserved motifs, but differ in having greater chain lengths (about twice as long) and in the location of Motif 3 at an N terminal location relative to the other motifs. It was proposed that the herpesvirus gene arose by intragenic duplication of a standard dUTPase coding sequence and subsequent loss of one copy of each motif from the double length chain, and that the resulting enzyme was active as a monomer. With knowledge of the trimeric 3D structure of standard dUTPases, it is possible to suggest transformations that occurred in evolutionary development of the herpesvirus dUTPase. The distinct location of Motif 3 can indeed be seen to be consistent with it contributing to a single intramolecular active site with the other motifs. Separately, the occurrence in herpesvirus dUTPases of around 20 to 40 additional residues between Motifs 4 and 5 allows the C-terminal Motif 5 to reach the active site intramolecularly. The driving force behind these evolutionary changes remains obscure. We speculate that they may have allowed acquisition of a novel, presently unknown function by the protein. Consistent with this idea is the observation that in Alpha- and Gammaherpesvirus dUTPases the original locus of Motif 3 is occupied by a distinct conserved sequence (Motif 6); perhaps this element constitutes part of a separate functional capability. Notably, the apparently orthologous protein in Betaherpesviruses lacks the standard motifs while Motif 6 is still present.     

Prism reflectors for high power lasers

A new type of laser reflector is described in which the laser beam is split by frustrated total internal reflection and the components combined again. It has the properties of high reflectivity, high damage resistance, wide bandwidth and variable reflectivity. The design of two particular reflectors is discussed and their performance evaluated. One of these reflectors has the property of lateral inversion of the reflected beam, which is found to aid transverse mode selection in a ruby laser. As an application of the reflectors, a damage free, single transverse mode, mode-locked ruby laser is described.     

Selective Homogeneous Palladium(0)-Catalyzed Hydrogenation of Alkynes to (Z)-Alkenes

Zero-valent palladium precatalysts containing rigid bidentate bis(arylimino)acenaphthene ligands (shown schematically) facilitate the highly stereoselective homogeneous catalytic hydrogenation of alkynes to (Z)-alkenes. Internal, terminal, aryl-substituted, and cyclic alkynes are suitable substrates, as are some enynes, which are chemoselectively hydrogenated to dienes. E=CO(2)Me; R(1), R(2)=4-OCH(3), 4-CH(3), 2,6-(CH(3))(2).     

Photoelastic determination of stresses in multiple-pin connectors

The design, fabrication, and testing of photoelastic models of double-lap, multiple-pin connectors are discussed. Interest is in the stresses in the inner laps. These stresses are determined by constructing models with photoelastic inner laps and transparent-acrylic outer laps. The connectors have two pins, in tandem, parallel to the load direction. A photoelastic-isotropic point is shown to permit the evaluation of load sharing between the two pins. A numerical scheme, utilizing the isochromatic- and isoclinic-photoelastic data and a finite-difference representation of the planestress equilibrium equations, is used to compute the stresses around the two pins. Representative stress distributions and stress-concentration factors are shown.     

Catalyst development for organocatalytic hydrosilylation of aromatic ketones and ketimines

A new family of Lewis basic 2-pyridyl oxazolines have been developed, which can act as efficient organocatalysts for the enantioselective reduction of prochiral aromatic ketones and ketimines with trichlorosilane, a readily available and inexpensive reagent. 1-Isoquinolyl oxazoline, derived from mandelic acid, was identified as the most efficient catalyst of the series, capable of delivering high enantioselectivities in the reduction of both ketones (up to 94% ee) and ketimines (up to 89% ee).     

A critical investigation of the effects of the radio frequency potential on the trapping of externally injected ions in ion trap mass spectrometry

The sensitivity of all ion trap mass spectrometry (ITMS) methods is dependent on the trapping efficiency of the instrument. For ITMS instruments utilizing external ion sources, such as laser desorption, trapping efficiency is known to depend on the phase and amplitude of the radio frequency (RF) potential applied to the ring electrode at the time of ion introduction. It is remarkable that, in a considerable body of literature, no consensus exists regarding the effects of these parameters on the efficacy of trapping externally generated ions. In this paper, a summary of the literature is presented in order to highlight significant discrepancies. New laser desorption ion trap mass spectrometry (LD-ITMS) data are also presented, from which conclusions are drawn in our effort to clarify some of the confusion. Copyright 1999 John Wiley & Sons, Ltd.     

Co-axially pumped,narrow band,continuously tunable,high power VUV xenon laser

High efficiency spectral narrowing to 0.13 nm and frequency tuning from 169 nm to 176 nm has been produced with a new design of coaxial-pumped xenon laser employing a single intra-cavity prism. The laser peak power is 3 MW (9 mJ) and becomes 0.7 MW (power density 10 MW cm^-2) when frequency narrowed.