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51.
Lee McIntyre 《Foundations of Chemistry》1999,1(1):57-63
After a long period of neglect, the philosophy of chemistry is slowly being recognized as a newly emerging branch of the philosophy of science. This paper endorses and defends this emergence given the difficulty of reducing all of the philosophical problems raised by chemistry to those already being considered within the philosophy of physics, and recognition that many of the phenomena in chemistry are epistemologically emergent. 相似文献
52.
Sally M. McIntyre Jill Wisnewski Ferguson Travis M. Witte R.S. Houk 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(3-4):248-254
The general method of comparing measured ion ratios to calculated ion ratios to determine a gas kinetic temperature (Tgas) is reviewed. Various mathematical refinements to the calculated partition functions are examined for their effect on the determined Tgas. It is found that (a) excited electronic states should be included for ArO+, neutral NO, and O2; (b) a 10% error in solvent load, sample gas flow rate, vibrational constant (ω), rotational constant (B) or measured ion ratio produces only a 1 to 3% error in Tgas; (c) a 10% error in dissociation energy (D0) creates nearly a 10% error in Tgas; and (d) high temperature corrections to the partition functions produce minimal change and can generally be neglected. 相似文献
53.
B.N. Littleton A.I. Bishop T.J. McIntyre P.F. Barker H. Rubinsztein-Dunlop 《Shock Waves》2000,10(3):225-228
Abstract. A non-intrusive laser-based method for direct velocity measurements has been demonstrated in a superorbital flow facility.
The method is based upon laser enhanced ionisation velocimetry in which a tagged region is created by two step excitation
of sodium and subsequent collisional ionisation. The achieved depletion of neutral atoms is then interrogated by planar laser
induced fluorescence. The velocities were measured in the freestream at a superorbital condition yielding km/s. These results compare favourably with the measured shock speeds in the facility.
Received 15 March 1999 / Accepted 2 March 2000 相似文献
54.
Francis JT Nie HY McIntyre NS Briggs D 《Langmuir : the ACS journal of surfaces and colloids》2006,22(22):9244-9250
In this paper, time-of-flight secondary ion mass spectrometry (ToF-SIMS) under static conditions was used to investigate self-assembled monolayers (SAMs) of octadecylphosphonic acid (OPA) formed on freshly cleaved muscovite mica substrates. The coverage of OPA on mica ranged from 20 to 100%, with a film thickness of 1.7+/-0.2 nm, which was determined by atomic force microscopy (AFM) imaging. The relative intensity of the specific secondary ion species associated with the OPA and with the exposed mica substrate exhibited good correlation with surface coverage. An excellent correlation was also observed (R2=0.98) between the relative SIMS [OPA-H]- intensity and the surface carbon concentration (OPA C 1s, in atomic %) from XPS at the prescribed surface coverage. The observation of positive and negative OPA molecular attachment of secondary ions involving the substrate species is discussed in terms of the chemical affinity of the OPA phosphonate headgroup for the cleaved mica surface as well as the sampling depth. In addition, the OPA molecular attachment species formed with the potassium ions on the cleaved mica substrate dominated the positive secondary ion mass spectrum in the high-mass range. A temperature-dependent, ToF-SIMS study employing in situ heating of a 100% coverage OPA monolayer revealed that the molecules begin to diffuse above approximately 80 degrees C, resulting in a decrease in the relative secondary ion yield of the OPA-specific secondary ions. This observation is hypothesized to be due to a decrease in the effective coverage of the substrate by the OPA molecules, which in turn could be due to the formation of multilayers upon heating in an effort to minimize the energy of the system. The interesting behavior of the novel OPA dimer species as a function of temperature is also reported. It was observed that the relative intensity of OPA and the mica-specific secondary ion peak intensities to that of Si (mica substrate) provides an effective means to estimate the change in coverage at elevated temperatures. 相似文献
55.
Carver G Dobe C Jensen TB Tregenna-Piggott PL Janssen S Bill E McIntyre GJ Barra AL 《Inorganic chemistry》2006,45(12):4695-4705
Spectroscopic, magnetochemical, and crystallographic data are presented for CsFe(H2O)6PO4, a member of a little-known isomorphous series of salts that facilitates the study of hexa-aqua ions in a quasicubic environment. Above 120 K, the deviations from cubic symmetry are minimal, as shown by the first example of an iron(II) M?ssbauer spectrum that exhibits no measurable quadrupole splitting. Two crystallographically distinct [Fe(OH2)6]2+ complexes are identified from inelastic neutron-scattering (INS) experiments conducted between 2 and 15 K. The data are modeled with the ligand-field Hamiltonian, H = lambdaL? + betaB(kL + 2?) + Delta(tet){Lz2 - (1/3)L(L + 1)} + Delta(rhom){Lx2 - Ly2}, operating in the ground-term (5)T(2g) (Oh) basis. An excellent reproduction of INS, M?ssbauer, HF-EPR, and magnetochemical data are obtained in the 2 and 15 K temperature regimes with the following parameters: lambda = -80 cm(-1); k = 0.8; site A Delta(tet) = 183 cm(-1), Delta(rhom)= 19 cm(-1); site B Delta(tet) = 181 cm(-1), Delta(rhom)= 12 cm(-1). The corresponding zero-field-splitting (ZFS) parameters of the conventional S = 2 spin Hamiltonian are as follows: site A D = 12.02 cm(-)(1), E = 2.123 cm(-1); site B D = 12.15 cm(-1), E = 1.37 cm(-1). A theoretical analysis of the variation of the energies of the low-lying states with respect to displacements along selected normal coordinates of the [Fe(OH2)6]2+, shows the zero-field splitting to be extremely sensitive to small structural perturbations of the complex. The expressions derived are discussed in the context of spin-Hamiltonian parameters reported for the [Fe(OH2)6]2+ cation in different crystalline environments. 相似文献
56.
57.
Douglas E. McIntyre D.John Faulkner Donna Van Engen Jon Clardy 《Tetrahedron letters》1979,20(43):4163-4166
The major antibacterial metabolite in the sponge sp. was shown to be an isoquinoline quinone, renierone (). The structure of renierone () was defined by X-ray crystallography. 相似文献
58.
Transition metal-doped titanium(IV) dioxide: Characterisation and influence on photodegradation of poly(vinyl chloride) 总被引:1,自引:0,他引:1
The effects of transition metal dopants (V(IV), V(V), Mn(II), Cr(III), Mo(V), and W(V)), introduced into TiO2, upon the rate of photodegradation of poly(vinyl chloride) (PVC) films containing TiO2 have been measured. The rates were determined mainly by monitoring carbonyl group formation. In another set of experiments, the rates of chloride ion release from irradiated PVC particles suspended in water undergoing agitation with air or O2 in the presence of particles of doped TiO2 were measured electrochemically. The doping of TiO2 (rutile) with Cr(III), V(V) or Mn(II) reduces the photoactivity of the pigment, while doping by Mo(V) or W(V) enhances its photoactivity; the results obtained from carbonyl index measurements are paralleled closely by those from chloride ion release. Even the most aggressive doped pigments were less reactive than Degussa P25 pigment, while the greatest protection to PVC film was offered by TiO2 particles coated with Al2O3 or SiO2. Overall, the photoactivity of doped TiO2 is a complex function of dopant concentration, the energy levels of the dopants in the TiO2 lattice, their d electronic configuration and their local distribution. Photoactivity is also linked to other factors such as crystal type, particle size distribution and surface area. There is a clear relationship between the tendency of the dopant to induce the rutile-to-anatase transition and its effect in enhancing the photoactivity of the pigment. The characterisation of the doped pigments was achieved using X-ray powder diffraction, EPR spectroscopy, diffuse reflectance UV-vis spectrophotometry, scanning optical and electron microscopy and particle size analysis using LALLS. 相似文献
59.
M. Paasch M. Winterlich R. Böhmer R. Sonntag G. J. McIntyre A. Loidl 《Zeitschrift für Physik B Condensed Matter》1995,99(3):333-338
The χ,T phase diagram of (NH4I)x(KI)1?x has been determined using neutron diffraction experiments and dielectric spectroscopy. At low temperatures and with decreasing χ, the sequence γ, β, ε and glass phase has been detected. The critical concentration χc≈0.55 separates the glassy phase with frozen-in orientational disorder from the ε phase which reveals long-range orientational order. Close to χc our experiments reveal evidence for two subsequent glass transitions. 相似文献
60.
Luis F Campo J Gómez J McIntyre GJ Luzón J Ruiz-Molina D 《Physical review letters》2005,95(22):227202
We use neutron diffraction to probe the magnetization components of a crystal of Mn12 single-molecule magnets. Each of these molecules behaves, at low temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the crystallographic c axis. The application of a magnetic field H(perpendicular) perpendicular to c induces quantum tunneling between opposite spin orientations, enabling the spins to attain thermal equilibrium. For T approximately < 0.9(1) K, this equilibrium state shows spontaneous magnetization, indicating the onset of ferromagnetism. These long-range magnetic correlations nearly disappear for mu0H(perpendicular) approximately > 5.5 T, possibly suggesting the existence of a quantum critical point. 相似文献