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JM Brown

Publications and source records attributed to JM Brown.

At least 19 recordsLinked to original sources
PubMed2001

A Study of the (2-0) Overtone Bands of the FO, BrO, and IO Free Radicals by Laser Magnetic Resonance.

The (2-0) overtone bands of the FO, BrO, and IO free radicals in their ground electronic state X(2)Pi(3/2) have been detected by laser magnetic resonance. The data obtained from this work have been fitted together with data from previous work. A set of molecular parameters, including vibrational, rotational, centrifugal distortion, spin-orbit, lambda-doubling, hyperfine, and Zeeman terms, has been determined for each molecule. Copyright 2001 Academic Press.

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PubMed2000

Catalytic asymmetric hydroboration/amination and alkylamination with rhodium complexes of 1,1'-(2-diarylphosphino-1-naphthyl)isoquinoline

Catecholboronate esters formed by asymmetric hydroboration of arylalkenes are not directly converted to amines by reaction with hydroxylamine-O-sulfonic acid. Prior conversion to a trialkylborane by reaction with ZnEt2 or MeMgCl permits a subsequent amination reaction to occur with essentially complete retention of configuration, leading to a range of primary alpha-arylalkylamines in up to 97% enantiomeric excess (ee). Secondary, but not tertiary amines may be formed by a related pathway when in situ generated alkylchloramines are employed as the aminating agent. The catalytic asymmetric hydroboration, beta-alkylation and amination steps may be combined in a single stage. Overall, this provides a practical procedure for the synthesis of enantiomerically enriched arylamines, exemplified inter alia by the synthesis of (S)-1,2,3,4-tetrahydro-1-naphthylamine in 95-97% ee and of (R)-N-(cyclohexyl)-1'-(4-methoxyphenyl)ethylamine in 93% ee.

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PubMed2000

Rotational Spectrum of the AsH(2) Radical in Its Ground State, Studied by Far-Infrared Laser Magnetic Resonance.

The rotational spectrum of AsH(2) in its ground &Xtilde;(2)B(1) electronic state has been recorded using a far-infrared laser magnetic resonance spectrometer. The AsH(2) radical was produced inside the spectrometer cavity by the reaction of arsine (AsH(3)) with fluorine atoms. Hyperfine splittings from both (75)As and (1)H nuclei were observed, and analysis of the spectra has yielded accurate values for rotational, hyperfine, and Zeeman parameters. Copyright 2000 Academic Press.

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PubMed2000

The Electronic Spectrum of Tellurium Dioxide.

The electronic spectrum of gas-phase tellurium dioxide has been recorded between 345 and 406 nm using the technique of laser-induced fluorescence spectroscopy. The TeO(2) sample was prepared by direct heating of the solid and by seeding it in a continuous free-jet expansion in argon. Twenty-seven cold bands and thirty-two hot bands were assigned. The wavenumbers of the band origin and symmetric stretching and bending vibrational modes for the upper and lower states were determined in a simple least-squares fit: nu(0) = 25526 cm(-1), omega(1)(') = 679 cm(-1), omega(2)(') = 220 cm(-1), omega(1)(") = 823 cm(-1), omega(2)(") = 282 cm(-1). Copyright 2000 Academic Press.

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PubMed2000

Far-Infrared Laser Magnetic Resonance Spectroscopic Study of the nu(2) Bending Fundamental of the CCN Radical in Its &Xtilde;(2)Pi(r) State.

Bending vibration-rotation transitions between the (010) µ(2)Sigma(-) and (000) (2)Pi(r) vibronic states of the CCN radical in its ground electronic state have been observed using far-infrared laser magnetic resonance (FIR LMR) spectroscopy. Thirteen FIR laser lines were used to record 769 resonances. The LMR data, combined with previous data, were used to determine vibrational, Renner-Teller, fine-structure, rotational, hyperfine, and molecular g-factor parameters using a least-squares fitting routine. The model used was an N(2) effective Hamiltonian modified to include the Renner-Teller effect explicitly in a (2)Pi electronic state. The band origin for the (010) µ(2)Sigma(-) <-- (000) &Xtilde;(2)Pi(r) transition was determined to be 179.598176 +/- 0.000067 cm(-1). The spin-orbit splitting in the ground state was refined and the complete set of (14)N-hyperfine parameters determined for the first time.

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PubMed2000

Fourier Transform Spectra of the E(2)Pi(u)-X(2)Pi(g)((3/2)) System of CuCl(2).

High-resolution Fourier transform spectra of the laser-induced fluorescence of (63)Cu(37)Cl(2) produced in a cell have been recorded following excitation of a single vibronic level of the E(2)Pi(u) electronic state. Fluorescence occurs in combination bands to a broad spread of levels in the ground electronic state. A global vibronic model is proposed for the ground state based on an effective Hamiltonian, which fits the experimental data (2782 fluorescence lines, lower state quantum numbers: v(1) = 0-6, v(2) = 0-2, v(3) = 0-6, and J = 4(1/2)-80(1/2)) to 0.019 cm(-1) rms error. Vibrational, rotational and Renner-Teller parameters are obtained (e.g., omega(2) = 95.195(36) cm(-1), B(e) = 0.055106(3) cm(-1), epsilon = -0.1893(28)). A revised value for the equilibrium internuclear distance Cu-Cl is deduced: r(e)(Cu-Cl) = 0.20341(3) nm. The energy diagram of vibronic levels in the ground state is plotted up to 4000 cm(-1). Copyright 2000 Academic Press.

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PubMed1999

Rotational Spectra of Conformers and Isotopomers of 1-Hydroxynaphthalene.

The rotational spectra of cis- and trans-1-hydroxynaphthalene and trans-1-DO-naphthalene have been recorded between 6 and 18 GHz using a pulsed microwave spectrometer. Most of the transitions detected are a type; hyperfine splittings from the electric quadrupole interaction were observed for some transitions of the deuterated isotopomer. The frequencies were well modeled with an S-reduced asymmetric rotor Hamiltonian. The rotational constants were determined much more accurately than previously. In addition, the quartic centrifugal distortion parameters were determined for the first time. Their values were very small, consistent with the rigid framework of this aromatic molecule. Theoretical calculations were carried out to support the assignment of the two forms to the cis and trans conformers. These calculations suggested that the cis conformer is slightly nonplanar in its equilibrium configuration, a property which is not inconsistent with its rotational constants. Copyright 1999 Academic Press.

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PubMed1999

Identification of New Hot Bands in the Blue and Green Band Systems of FeH.

A particularly rich region of the electronic spectrum of FeH from 525 to 545 nm was investigated using the techniques of dispersed and undispersed laser-induced fluorescence. Analysis has led to the discovery that several different electronic transitions are embedded in this region; the (0, 0) and (1, 1) bands of the e(6)Pi-a(6)Delta (green) system, the (0, 2) band of the g(6)Phi-X(4)Delta (intercombination) system, the (0, 1) band of the g(6)Phi-a(6)Delta (blue) system, and the (0, 0) band of the g(6)Phi-b(6)Pi system. Seventy-five lines were assigned in the (0, 1) band of the g(6)Phi-a(6)Delta transition. These, with the assignment of an additional 14 lines in the 583 nm region to the (0, 1) band of the e(6)Pi-a(6)Delta transition, led to the extension of the known term values to higher J values for the Omega = 9/2, 7/2, and 5/2 spin components of the v = 1 level of the a(6)Delta state and the novel characterization of the a(6)Delta(3/2) (v = 1) and g(6)Phi(5/2) (v = 0) components. A further 73 lines were assigned to the first four subbands of the (1, 1) band of the e(6)Pi-a(6)Delta transition and term values for the lowest four spin components of the v = 1 level of the e(6)Pi state were determined. This provides the first experimental measurement of a vibrational interval in one of the higher lying electronic states of FeH. The interval does not appear to vary strongly between the spin components (DeltaG(1/2) = 1717, 1713, 1710 cm(-1) for Omega = 7/2, 5/2, 3/2, respectively). Remarkably few of the hot-band transitions assigned in this work could be identified in the complex, high-temperature spectrum of FeH recorded by P. McCormack and S. O'Connor [Astron. Astrophys. Suppl. 26, 373-380 (1976)]. Copyright 1999 Academic Press.

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PubMed1998

Dispersed Fluorescence from the 460-nm Band System of NiCl2: Observation of a New, Low-Lying Electronic State.

The dispersed fluorescence spectrum of lines in the 460 nm band system of NiCl2 (nickel dichloride) is presented. The fluorescence was pumped on single rotational transitions of two spin components in a vibrational band observed previously in the laser excitation spectrum. Fluorescent transitions to levels of the &Xtilde;3Sigma-g (ground) state are assigned and discussed. The spectra also show clear evidence for a previously unidentified low-lying electronic state, assumed to be the à state, which lies about 2000 cm-1 above the ground state. This is likely to be of 3Pig character and is discussed on that basis. The wavenumber of the symmetric stretching vibration of NiCl2 in the à state is determined to be 367 cm-1, slightly larger than the &Xtilde; state value (360 cm-1). Copyright 1998 Academic Press.

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PubMed1998

Laser Excitation Spectroscopy of the &Btilde;2A1-&Xtilde;2A1 Transition of the CaOCH3 Radical.

The (0-0) band of the &Btilde;2A1- &Xtilde;2A1 transition of CaOCH3 at 565 nm has been recorded and analyzed at Doppler limited resolution (FWHM = 0.005 cm-1). The molecule was generated using a laser ablation/molecular beam source in which a solid calcium rod was ablated and a mixture of argon seeded with a few percent of methanol was used as the carrier gas. The rotational analysis of the band is consistent with a linear Ca-O-C geometry in both electronic states. Values for the spin-rotation parameters are determined for the excited &Btilde;2A1 state. Copyright 1998 Academic Press.

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PubMed1998

New Assignments in the Green and Red Band Systems of the FeH Radical.

The electronic spectrum of FeH in the regions of the 532 nm (green) and 630 nm (red) systems has been investigated using the techniques of dispersed and undispersed laser induced fluorescence. Sixteen lines have been assigned in the Omega = 1/2 <-- Omega = -1/2 subband of the e6Pi-c6Sigma+ transition and term values determined for the previously uncharacterized e6Pi1/2 spin-orbit component. A further fourteen lines were assigned to the connected Omega = 1/2 <-- Omega = 3/2 subband of the e6Pi-a6Delta transition and term values for the hitherto uncharacterized a6Delta3/2 component were determined. A study of the high-temperature spectrum of FeH, recorded previously by McCormack and O'Connor (1), enabled the branches of the Omega = 7/2 <-- Omega = 9/2 subband of the e6Pi-a6Delta transition to be extended to higher J values. These predictions were confirmed by laser induced fluorescence (LIF) experiments and led to the assignment of 13 additional lines in this subband. The term values for the e6Pi7/2 and a6Delta9/2 spin-orbit components were thus extended to higher J values. Copyright 1998 Academic Press.

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PubMed1997

Laser Excitation Spectroscopy of the A 3 Piu -X ; 3 Sigmag - Transition of the NCN Radical

The (010)-(010) band of the A 3 Piu -X ; 3 Sigmag - transition of the NCN radical at 328 nm has been reexamined at Doppler-limited resolution by laser excitation spectroscopy. The molecule was generated in a microwave discharge through N2 and CF4 in helium. Both the 3 Deltag -3 Piu and the 3 Sigmag +/- -3 Piu vibronic components of the transition have been observed and rotationally analyzed. The Renner-Teller parameter, varepsilonomega2 , for NCN in the excited A 3 Piu state is determined to be -91.1213(16) cm-1 . Estimates for the ground and excited state bending vibrational wavenumbers of 437.7(14) and 533.95(70) cm-1 respectively have been obtained.

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PubMed1996

Hypoxia-Specific Cytotoxins in Cancer Therapy.

Hypoxic-specific cytotoxins are a new, and as yet clinically untested, mode of treatment of solid tumors. If they can be given at high enough concentrations and sufficiently often, they should prove extremely effective both in combination with standard radiotherapy and also with certain chemotherapeutic drugs. It is likely that their optimum use will turn hypoxic cells in solid tumors from a therapeutic disadvantage to an advantage. In this report, we review the rationale for the use of hypoxia- cytotoxins, including both the theoretical basis for combining them with fractionated radiation and the preclinical results that have been obtained to date combing these agents with fractionated radiation. We also discuss the three major classes of bioreductive drugs, including the quinones (mitomycin C, porfiromycin, and E09), notroaromatic compounds (including RB6145 and various deoxyribonucleic acid [DNA] targeted aromatics), and finally the n-oxides of which tirapazamine is the lead compound. We also briefly discuss new approaches to bioreductive drug development. The best ways to use these agents are also covered. These include using them in combination with radiation, in combination with chemotherapy, and in combination with agents that increase tumor hypoxia. Finally, the importance of the selection of patients for clinical trials is illustrated by showing how dramatically the number of patients for clinical trials is illustrated by showing how dramatically the number of patients in a clinical trial has to increase to obtain statistical significance for a procedure targeted towards hypoxic cells if some of the patients in the trials have well-oxygenated tumors.

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