Chemistry and Physics publications
Permanent URI for this collection
Browse
Browsing Chemistry and Physics publications by Issue Date
Now showing 1 - 20 of 1746
Results Per Page
Sort Options
Item Metadata only Laser-induced fluorescence of gaseous vanadium methylidyne, VCH : A triatomic organometallic molecule(Amer Chemical Soc, 1995) Barnes, M.; Hajigeorgiou, P.; Kasrai, R.; Merer, A.; Metha, G.Item Open Access Electronic transitions of cobalt carbide, CoC, near 750 nm: a good example of case (b(βS)) hyperfine coupling(Amer Inst Physics, 1995) Barnes, M.; Merer, A.; Metha, G.The laser induced fluorescence spectrum of jet-cooled CoC near 750 nm has been measured at high resolution following the reaction of laser-ablated cobalt atoms with methane. The X2Σ+ ground state of CoC is an unusually good example of Hund’s case (bβS) coupling. Since Co has a nuclear spin I=7/2, each rotational level is split by the Fermi contact interaction into G=3 and G=4 components, where G=I+S; the splitting for N=0 is more than 0.5 cm−1. The X2Σ+ state begins to uncouple toward case (bβJ) with increasing rotation. Transitions to various 2Π excited states occur in the region 13 000–14 500 cm−1; the most prominent of these (for which high resolution spectra have been recorded) lie at 13 079 cm−1 (2Π3/2) and 13 343 cm−1 (2Π1/2). The (bβS) coupling in the ground state produces some unexpected hyperfine intensity patterns, which have been studied in detail. A very low-lying 2Δi state, whose Ω=5/2 and Ω=3/2 components lie at 221 and 1173 cm−1, has been identified. Laser excitation of the 2Π3/2–2Δ5/2 transition has been observed by monitoring the strong 2Π3/2–X2Σ+ emission, which has allowed the 2Δ5/2 state to be characterized at high resolution. A total of 879 rotational-hyperfine transitions between the various 2Π1/2, 2Π3/2, 2Δ5/2, and 2Σ+ states have been assigned and fitted. Matrix elements for a 2Σ+ state in case (bβS) coupling are listed.Item Metadata only A theoretical study of propagation rate coefficients for methacrylonitrile and acrylonitrile(American Chemical Society, 1998) Huang, D.M.; Monteiro, M.J.; Gilbert, R.G.The propagation rate coefficients for methacrylonitrile (MAN) and acrylonitrile (AN) were calculated using transition state theory and high-level ab initio molecular orbital theory. The calculations take particular account of internal rotations in the transition states. Frequency factors and rotational potentials were found to be insensitive to the level of theory used (except that the semiempirical AM1 method does not perform very well), because of cancellations in the partition function ratio in transition state theory; however, two of the internal rotations studied were found to be sensitive to the chain length of the radical used in the calculations. Activation energies were found to be extremely sensitive to the level of theory. At the highest level of theory used, the calculated frequency factor for MAN was slightly lower than experiment, while the activation energy was 2.6 kJ mol⁻¹ higher than experiment. Theoretical comparison of propagation of MAN and AN was used to explain differences observed experimentally in activation energies and frequency factors of methacrylates and corresponding acrylates. The higher frequency factors for methacrylates are largely due to hindrance caused by the methyl groups to the three transitional modes in the transition state which correspond to the three external rotational degrees of freedom of the monomer in the reactants (but not a result of increased hindrance to methyl rotation itself in the transition state). The higher activation energies of methacrylates arises from differences in hindrance and loss of delocalization in the transition states of the methyl-substituted and unsubstituted monomers.Item Metadata only Synthesis and hybridization properties of oligonucleotides containing 6-membered azasugar nucleotides(Pergamon Press, 1999) Jung, K.E.; Kim, K.; Yang, M.; Lee, K.; Lim, H.Abstract not availableItem Metadata only Several crucial problems in evaluating spectra of baryons with two heavy quarks(Science Press, 2000) Tong, Sheng-Ping; Ding, Yi-Bing; Guo, Xuhong; Jin, Hong-Ying; Li, Xue-Qian; Shen, Peng-Nian; Zhang, Ruibin; School of Chemistry and PhysicsItem Open Access Evidence for TeV gamma-ray emission from the shell type SNR RXJ1713.7-3946(E D P Sciences, 2000) Muraishi, H.; Tanimori, T.; Yanagita, S.; Yoshida, Y.; Moriya, M.; Kifune, T.; Dazeley, S.; Edwards, P.; Gunji, S.; Hara, S.; Hara, T.; Kawachi, A.; Kubo, H.; Matsubara, Y.; Mizumoto, Y.; Mori, M.; Muraki, Y.; Naito, T.; Nishijima, K.; Patterson, J.; et al.We report the results of TeV gamma-ray observations of the shell type SNR RXJ1713.7-3946 (G347.3-0.5). The discovery of strong non-thermal X-ray emission from the northwest part of the remnant strongly suggests the existence of electrons with energies up to 100 TeV in the remnant, making the SNR a good candidate TeV gamma-ray source. We observed RXJ1713.7-3946 from May to August 1998 with the CANGAROO 3.8m atmospheric imaging Cerenkov telescope and obtained evidence for TeV gamma-ray emission from the NW rim of the remnant with the significance of 5.6 sigma. The observed TeV gamma-ray flux from the NW rim region was estimated to be (5.3 +/- 0.9[statistical] +/- 1.6[systematic]) * 10^{-12} photons cm^{-2} s^{-1} at energies >= 1.8 +/- 0.9 TeV. The data indicate that the emitting region is much broader than the point spread function of our telescope. The extent of the emission is consistent with that of hard X-rays observed by ASCA. This TeV gamma-ray emission can be attributed to the Inverse Compton scattering of the Cosmic Microwave Background Radiation by shock accelerated ultra-relativistic electrons. Under this assumption, a rather low magnetic field of 11 micro gauss is deduced for the remnant from our observation.Item Metadata only Spinors in physics(2000) Szekeres, Peter; School of Chemistry and PhysicsItem Metadata only Structure and production of lambda baryons in a diquark model(World Scientific, 2000) Boros, Csaba Ladislaus Laszlo; Workshop on Lightcone QCD and Nonperturbative Hadron Physics (9th : 1999 : Adelaide, Australia); School of Chemistry and PhysicsItem Metadata only Novel diode laser-based sensors for gas sensing applications(MAIK Nauka/Interperiodica, 2000) Tittel, F.; Lancaster, D.; Richter, D.The development of compact spectroscopic gas sensors and their applications to environmental sensing will be described. These sensors employ mid-infrared difference-frequency generation (DFG) in periodically poled lithium niobate (PPLN) crystals pumped by two single-frequency solid state lasers such as diode lasers, diode-pumped solid state, and fiber lasers. Ultrasensitive, highly selective, and real-time measurements of several important atmospheric trace gases, including carbon monoxide, nitrous oxide, carbon dioxide, formaldehyde [correction of formaldehye], and methane, have been demonstrated.Item Metadata only On parametrically excited flexural motion of an extensible and shearable rod with a heavy attachment(Technische Universitaet Otto Von Guericke, 2000) Cull, S. J.; Tucker, Robin W.; Tung, R. S.; Hartley, David H.; School of Chemistry and PhysicsItem Metadata only Gluon and quark propagators in Landau gauge from the lattice(World Scientific, 2000) Williams, A.; Bowman, P.; Bonnet, F.; Leinweber, D.; Skullerud, J.; Workshop on Lightcone QCD and Nonperturbative Hadron Physics (9th : 1999 : Adelaide, Australia); Schreiber, A.; Williams, A.Item Metadata only Einstein and religion(2000) Szekeres, Peter; School of Chemistry and PhysicsItem Metadata only Temperature and length scale dependence of hydrophobic effects and their possible implications for protein folding(National Academy of Sciences, 2000) Huang, D.; Chandler, D.The Lum–Chandler–Weeks theory of hydrophobicity [Lum, K., Chandler, D. & Weeks, J. D. (1999) J. Phys. Chem. 103, 4570–4577] is applied to treat the temperature dependence of hydrophobic solvation in water. The application illustrates how the temperature dependence for hydrophobic surfaces extending less than 1 nm differs significantly from that for surfaces extending more than 1 nm. The latter is the result of water depletion, a collective effect, that appears at length scales of 1 nm and larger. Because of the contrasting behaviors at small and large length scales, hydrophobicity by itself can explain the variable behavior of entropies of protein folding.Item Metadata only Chiral symmetry, the lattice and the light-cone(World Scientific, 2000) Thomas, A.; Workshop on Lightcone Workshop on Lightcone QCD and Nonperturbative Hadron Physics (9th : 1999 : Adelaide, S. Aust.); Schreiber, A.; Williams, A.Item Metadata only Experiment will examine gravity waves in the middle atmosphere(American Geophysical Union, 2000) Hamilton, K.; Vincent, R.Over the last 4 decades, the study of high-frequency gravity waves with periods from minutes to several hours in the stratosphere, mesosphere, and lower thermosphere has been a leading area of research in both meteorology and aeronomy. This interest has been natural, since gravity wave motions often dominate the variance observed in the upper mesospheric and thermospheric wind field, and since the vertical transport of mean flow momentum by gravity waves is now thought to play a key role in maintaining global-scale circulation throughout the middle atmosphere. Part of the spectrum of the gravity waves propagating upward through the mesosphere will reach F-layer heights, where the gravity waves account for temporal and spatial variability in electron density Electron density, in turn, can affect aspects of radio wave propagation. Gravity waves in the equatorial F-region may also trigger large-scale ionospheric instabilities, which account for the “spread-F” phenomenon. Late next year, investigators involved in the Darwin Area Wave Experiment (DAWEX) will make detailed coordinated observations of the gravity wave field in the mesosphere and thermosphere with unprecedented areal coverage, and will attempt to relate these observations to a particularly well-defined and intense tropospheric sourceItem Metadata only Temperature and length scale dependence of hydrophobic effects and their possible implications for protein folding(National Academy of Sciences, 2000) Huang, D.M.; Chandler, D.The Lum–Chandler–Weeks theory of hydrophobicity [Lum, K., Chandler, D. & Weeks, J. D. (1999) J. Phys. Chem. 103, 4570–4577] is applied to treat the temperature dependence of hydrophobic solvation in water. The application illustrates how the temperature dependence for hydrophobic surfaces extending less than 1 nm differs significantly from that for surfaces extending more than 1 nm. The latter is the result of water depletion, a collective effect, that appears at length scales of 1 nm and larger. Because of the contrasting behaviors at small and large length scales, hydrophobicity by itself can explain the variable behavior of entropies of protein folding.Item Open Access Cavity formation and the drying transition in the Lennard-Jones fluid(American Physical Society, 2000) Huang, D.M.; Chandler, D.By simulation and theory, we study the probability of observing N molecular centers within molecular sized volumes for a Lennard-Jones fluid near liquid-vapor coexistence. For large volumes and small N, the probability distribution differs markedly from Gaussian. The free energy per unit surface area to form empty volumes (i.e., cavities) is a rapidly varying function of the radius for small cavities. It becomes constant for large volumes. The source of these behaviors is the occurrence of drying (i.e., solvent depletion) at the cavity surface. The crossover to drying occurs on microscopic length scales, with significant density depletion found for cavities with radii of the order of two or more Lennard-Jones diameters. Reasonable agreement is found between the simulation results and the theory developed by Lum, Chandler, and Weeks [J. Phys. Chem. B 103, 4570 (1999)].Item Metadata only Cosmic ray-induced high energy gamma-ray emission: a background for WIMP annihilation and massive relic particle models of UHE CR(ICRC, 2001) Porter, T.; Protheroe, R.; International Cosmic Ray Conference (27th : 2001 : Hamburg, Germany)The possible discovery of a diffuse galactic halo in GeV gamma-rays has led to several possible dark matter explanations. An important consideration for these models is the uncertainty in the galactic diffuse gamma-ray background. For example, the predicted inverse Compton signal can vary significantly depending on the choice of cosmic ray halo size, or even on the electron injection spectral index. Using a self-consistent propagation model we calculate the distribution of galactic cosmic ray electrons and positrons. Diffuse gamma-ray spectra are obtained using the results of the propagation calculations. We show our results for different propagation model parameters and electron injection spectral indices.Item Metadata only Cherenkov pulse shape measurements of primary composition(2001) Sinnott, M.; Clay, R.; Protheroe, R.; Thornton, G.; Patterson, J.; International Cosmic Ray Conference (27th : 2001 : Hamburg, Germany)The primary cosmic ray spectrum lies relatively unexplored in the energy range 10 - 100 TeV. Satellite experiments suffer from poor statistics in probing high energies, and ground-based particle arrays are limited by their operating thresholds from getting down to the lower energy events. An atmospheric Cherenkov telescope can maintain a sufficiently large collecting area at these energies and is able to probe higher energies through large zenith angle observations. Structure in the leading edge of the Cherenkov time profile (of hadron induced cascades) is investigated as a possible discriminator of cosmic ray species. Experimental results are presented.Item Metadata only Separation of mass-overlapped time of flight-energy elastic recoil detection analysis data using Ryan and Jamieson's dynamic analysis method(Elsevier Science BV, 2001) Persson, Leif; Whitlow, Harry J.; Bouanani, Mohamed El; Hult, Mikael; Andersson, Margaretha; Bubb, Ian F.; Cohen, David D.; Dytlewski, Nick; Johnston, Peter N.; Walker, Scott Raymond; Zaring, Carina; Ostling, Mikael; School of Chemistry and PhysicsTime of flight-energy (ToF-E) elastic recoil detection analysis (ERDA) data often contains mass signals with considerable overlap from adjacent isotopes in the mass-energy plane. An evaluation has been carried out of the suitability of the dynamic analysis method proposed by Ryan and Jamieson to decompose elemental signals with overlapping mass. This method is shown to work very well on generated test data and the result when it was applied to experimental data appears quite promising. Very accurate mass calibration and lineshape determination was found to be a prerequisite for the application of the method.