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51.
We demonstrate mid-infrared spectroscopy of large molecules with broad absorption features using a tunable external cavity quantum cascade laser. Absorption spectra for two different Freons are measured over the range 1130-1185 cm(-1) with 0.2 cm(-1) resolution via laser photoacoustic spectroscopy with quartz tuning forks as acoustic transducers. The measured spectra are in excellent agreement with published reference absorption spectra. 相似文献
52.
Dr. Joshua Britton Prof. Dr. Timothy F. Jamison 《Angewandte Chemie (International ed. in English)》2017,56(30):8823-8827
A rapid and modular continuous flow synthesis of highly functionalized fluorinated pyrazoles and pyrazolines has been developed. Flowing fluorinated amines through sequential reactor coils mediates diazoalkane formation and [3+2] cycloaddition to generate more than 30 azoles in a telescoped fashion. Pyrazole cores are then sequentially modified through additional reactor modules performing N-alkylation and arylation, deprotection, and amidation to install broad molecular diversity in short order. Continuous flow synthesis enables the safe handling of diazoalkanes at elevated temperatures, and the use of aryl alkyne dipolarphiles under catalyst-free conditions. This assembly-line synthesis provides a flexible approach for the synthesis of agrochemicals and pharmaceuticals, as demonstrated by a four-step, telescoped synthesis of measles therapeutic, AS-136A, in a total residence time of 31.7 min (1.76 g h−1). 相似文献
53.
We derive a model for the dissociative chemisorption of methane on a Ni(100) surface, based on the reaction path Hamiltonian, that includes all 15 molecular degrees of freedom within the harmonic approximation. The total wavefunction is expanded in the adiabatic vibrational states of the molecule, and close-coupled equations are derived for wave packets propagating on vibrationally adiabatic potential energy surfaces, with non-adiabatic couplings linking these states to each other. Vibrational excitation of an incident molecule is shown to significantly enhance the reactivity, if the molecule can undergo transitions to states of lower vibrational energy, with the excess energy converted into motion along the reaction path. Sudden models are used to average over surface impact site and lattice vibrations. Computed dissociative sticking probabilities are in good agreement with experiment, with respect to both magnitude and variation with energy. The ν(1) vibration is shown to have the largest efficacy for promoting reaction, due to its strong non-adiabatic coupling to the ground state, and a significant softening of the vibration at the transition state. Most of the reactivity at 475 K is shown to result from thermally assisted over-the-barrier processes, and not tunneling. 相似文献
54.
Acosta-Gutiérrez S Hernández-Rojas J Bretón J Llorente JM Wales DJ 《The Journal of chemical physics》2011,135(12):124303
Likely candidates for the lowest minima of water clusters (H(2)O)(N) for N ≤ 20 interacting with a uniform electric field strength in the range E ≤ 0.6 V/? have been identified using basin-hopping global optimization. Two water-water model potentials were considered, namely TIP4P and the polarizable Dang-Chang potential. The two models produce some consistent results but also exhibit significant differences. The cluster internal energy and dipole moment indicate two varieties of topological transition in the structure of the global minimum as the field strength is increased. The first takes place at low field strengths (0.1 V/? 10) usually forming helical structures. 相似文献
55.
West NP Cergol KM Xue M Randall EJ Britton WJ Payne RJ 《Chemical communications (Cambridge, England)》2011,47(18):5166-5168
The first targeted inhibitors of an essential M. tuberculosis cell wall lipase, Rv3802c, are described. Lead compounds exhibited nanomolar inhibition of the enzyme, and encouraging antibacterial activity against M. tuberculosis in vitro, supporting Rv3802c as a novel TB drug target. 相似文献
56.
Britton Chang Anne Greenbaum Eric Machorro 《Numerical Linear Algebra with Applications》2011,18(1):141-154
In this paper, we prove that the piecewise bilinear Petrov‐Galerkin discretization for the mono‐directional neutron transport equation described in (J. Comput. Phys. 1986; 64 :96–111) is convergent and second‐order accurate, provided that the true solution to the problem has continuous partial derivatives of all orders up through three. We do this by giving a bound on the 2‐norm of the inverse of the system matrix that is independent of the mesh size. This shows that the global error is of the same order as the local truncation error. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
57.
58.
The 195Pt and 13C chemical shifts (δPt and δc) are reported for platinum(II), platinum(IV) and class II mixed-valence complexes, with general formula [PtL4]X2, cis- and trans-PtL2X2, PtL2X4 and Pt2L4X6 (where L may be thiourea, 2-imidazolidine-thione, tetrahydro 2-pyrimidinethione, thiocaprolactam, pyridine-2-thione and tetramethylthiourea, and X may be Cl or Br). The 195Pt chemical shifts can be understood in view of 13C data in terms of variations of electronegativities and σ-donor abilities of ligands attached to platinum. 相似文献
59.
CO, excited to its seventh vibrational level, is generated by C oxidation on Pt at 1000–1400 K. Analysis of its Fourier transform IR emission spectrum suggests a non-equilibrium, yet statistical, vibrational distribution. A long-lived reaction complex involving 2–3 Pt atoms is postulated. 相似文献
60.
A. T. Britton J. L. Sullivan K. J. Smith 《Journal of Polymer Science.Polymer Physics》1980,18(3):537-546
Thermoelasticity studies of poly(vinyl alcohol) networks swollen in aqueous glycol indicate that the effects of specific polymer-diluent interactions diminish at high swelling, much as in the situation of poly(vinyl alcohol) in pure water reported earlier. In 20% glycol, the ratio of the energy component fe of the force to the total force f was found to be ?0.59 at high swelling. Swelling was controlled by the degree of network crosslinking. Evidence that fe/f could be determined under the condition of a null thermal expansion coefficient was not obtained; in fact, the contrary was indicated. 相似文献