Kinetics following addition of sulfur fluorides to a weakly ionized plasma from 300 to 500 K: rate constants and product determinations for ion-ion mutual neutralization and thermal electron attachment to SF5, SF3, and SF2

Rate constants for several processes including electron attachment to SF(2), SF(3), and SF(5) and individual product channels of ion-ion mutual neutralization between SF(6)(-), SF(5)(-), and SF(4)(-) with Ar(+) were determined by variable electron and neutral density attachment mass spectrometry. The experiments were conducted with a series of related neutral precursors (SF(6), SF(4), SF(5)Cl, SF(5)C(6)H(5), and SF(3)C(6)F(5)) over a temperature range of 300-500 K. Mutual neutralization rate constants for SF(6)(-), SF(5)(-), and SF(4)(-) with Ar(+) are reported with uncertainties of 10-25% and show temperature dependencies in agreement with the theoretical value of T(-0.5). Product branching in the mutual neutralizations is temperature independent and dependent on the electron binding energy of the anion. A larger fraction of product neutrals from the SF(6)(-) mutual neutralization (0.9 ± 0.1) are dissociated than in the SF(5)(-) mutual neutralization (0.65 ± 0.2), with the SF(4)(-) (0.7 ± 0.3) likely lying in between. Electron attachment to SF(5) (k = 2.0 × 10(-8) ±(1)(2) cm(3) s(-1) at 300 K) and SF(3) (4 ± 3 × 10(-9) cm(3) s(-1) at 300 K) show little temperature dependence. Rate constants of electron attachment to closed-shell SF(n) species decrease as the complexity of the neutral decreases.     

Kinetics of electron attachment to SF3CN, SF3C6F5, and SF3 and mutual neutralization of Ar+ with CN- and C6F5(-)

The additions of two sulfur fluoride derivatives (SF(3)C(6)F(5) and SF(3)CN) to a flowing afterglow were studied by variable electron and neutral density mass spectrometry. Data collection and analysis were complicated by the high reactivity of the neutral species. Both species readily dissociatively attach thermal electrons at 300 K to yield SF(3) + X(-) (X = C(6)F(5), CN). Attachment to SF(3)C(6)F(5) also results in SF(3)(-) + C(6)F(5) as a minor product channel. The determined electron attachment rate constants were 1(-0.6) (+1) × 10(-7) cm(3) s(-1) for SF(3)C(6)F(5), a lower limit of 1 × 10(-8) cm(3) s(-1) for SF(3)CN, and 4 ± 3 × 10(-9) cm(3) s(-1) for SF(3). Mutual neutralization rate constants of C(6)F(5)(-) and CN(-) with Ar(+) at 300 K were determined to be 5.5(-1.6) (+1.0) × 10(-8) and 3.0 ± 1 × 10(-8) cm(3) s(-1), respectively.     

Pressure and temperature dependence of dissociative and non-dissociative electron attachment to CF3: experiments and kinetic modeling

The kinetics of electron attachment to CF(3) as a function of temperature (300-600 K) and pressure (0.75-2.5 Torr) were studied by variable electron and neutral density attachment mass spectrometry exploiting dissociative electron attachment to CF(3)Br as a radical source. Attachment occurs through competing dissociative (CF(3) + e(-) → CF(2) + F(-)) and non-dissociative channels (CF(3) + e(-) → CF(3)(-)). The rate constant of the dissociative channel increases strongly with temperature, while that of the non-dissociative channel decreases. The rate constant of the non-dissociative channel increases strongly with pressure, while that of the dissociative channel shows little dependence. The total rate constant of electron attachment increases with temperature and with pressure. The system is analyzed by kinetic modeling in terms of statistical theory in order to understand its properties and to extrapolate to conditions beyond those accessible in the experiment.     

Dissociation dynamics and thermochemistry of tin species, (CH3)4Sn and (CH3)6Sn2, by threshold photoelectron-photoion coincidence spectroscopy

The dissociative photoionization of tetramethyltin (Me?Sn) and hexamethylditin (Me?Sn?) has been investigated by threshold photoelectron-photoion coincidence (TPEPICO). Ions are energy-selected, and their 0 K dissociation onsets are measured by monitoring the mass spectra as a function of ion internal energy. Me?Sn(+) dissociates rapidly by methyl loss, with a 0 K onset of E? = 9.382 ± 0.020 eV. The hexamethylditin ion dissociates slowly on the time scale of the experiment (i.e., during the 40 μs flight time to the detector) so that dissociation rate constants are measured as a function of the ion energy. RRKM and the simplified statistical adiabatic channel model (SSACM) are used to extrapolate the measured rate constants for methyl and Me?Sn(?) loss to their 0 K dissociation onsets, which were found to be 8.986 ± 0.050 and 9.153 ± 0.075 eV, respectively. Updated values for the heats of formation of the neutral Me?Sn and Me?Sn? are used to derive the following 298.15 K gas-phase standard heats of formation, in kJ·mol?1: Δ(f)H(m)(o)(Me?Sn(+),g) = 746.3 ± 2.9; Δ(f)H(m)(o)(Me?Sn?(+),g) = 705.1 ± 7.5; Δ(f)H(m)(o)(Me?Sn(?),g) = 116.6 ± 9.7; Δ(f)H(m)(o)(Me?Sn,g) = 123.0 ± 16.5; Δ(f)H(m)(o)(MeSn(+),g) = 877.8 ± 16.4. These energetic values also lead to the following 298.15 K bond dissociation enthalpies, in kJ·mol?1: BDE(Me?Sn-Me) = 284.1 ± 9.9; BDE(Me?Sn-SnMe?) = 252.6 ± 14.8.     

The Weak Chebyshev X-Greedy Algorithm in the unweighted Bergman space

We study a greedy algorithm called the Weak Chebyshev X-Greedy Algorithm (WCXGA) and investigate its application to unweighted Bergman spaces. We first show that the WCXGA converges for a wide class of real and complex Banach spaces and dictionaries. We then prove that certain Bergman spaces and their holomorphic monomial dictionaries belong to the class of Banach spaces for which the WCXGA converges.     

Complex formation thermodynamics of some metal(II) phenyl-2-pyridylketoximates

The formation of phenyl-2-pyridylketoximates of nickel(II), zinc(II), cadmium-(II), mercury(II) and lead(II) was studied potentiometrically in a medium of 40% (w/w) acetone and 60% (w/w) water. The values of step formation constants, free energy, entropy and enthalpy of complex formation were calculated. The formation of the mercury chelate was found to be entropy driven. The formation of phenyl-2-pyridylketoximates of other metals of the first transitional series could not be studied owing to experimental difficulties.     

Magnetic properties of nickel clusters in nanoporous carbon

The magnetic properties of nanoporous carbon samples whose pores were loaded by nickel are described. It is shown that a sample becomes superparamagnetic for temperatures T<T _C (Ni) only in the case where a noticeable fraction of Ni is contained in the nanopores. The nanopore size estimated from magnetic measurements coincides with the estimates derived earlier from small-angle x-ray scattering studies.     

Cyclodextrin as a capturing agent for redundant surfactants on Ag nanoparticle surface in phase transfer process

High-yield phase transfer of hydrophilic mercaptosuccinic acid (MSA)-modified Ag nanoparticles into chloroform is readily attained using cetyltrimethylammonium bromide (CTAB) through electrostatic interaction. Increasing CTAB amount to a certain degree has achieved nearly complete phase transfer due to the sufficient formation of stoichiometric ion-pairs on particle surface. However, at high CTAB concentration, some unbonded CTA⁺ cations will be physically adsorbed on particle surface and enter chloroform layer simultaneously, which cannot be removed by simple water washing or centrifugation. By using β-cyclodextrin (CD) as a capturing agent, this portion of CTA⁺ cations can be adequately removed due to the possible inclusion function of CD. Upon removal of the unbonded CTAB, the monolayer formation of phase-transferred Ag nanoparticles at air–water interface presents improved two-dimensional (2D) orderliness owing to the more effective interdigitation among adjacent particles.     

Syntheses of 6,8-disubstituted-9-β-D-ribofuranosylpurine 3′,5′-cyclic phosphates

A series of 6,8-disubstituted-9-β-D-ribofuranosylpurine 3′,5′-cyclic phosphates were prepared employing preformed 9-β-D-ribofuranosylpurine 3′,5′-cyclic phosphate precursors. Three synthetic approaches were utilized to accomplish the syntheses. The first approach involved a study of the order of nucleophilic substitution, 6 vs 8, of the intermediate 6,8-dichloro-9-β-D-ribofuranosyipurine 3′,5′-cyclic phosphates ( 2 ) with various nucleophilic agents to yield 8-amino-6-chloro-, 8-chloro-6-(diethylamino)-, 6-chloro-8-(diethylamino)-, 6,8-bis-(diethylamino)- and 8-(benzylthio)-6-chloro-9-β-D-ribofuranosylpurine 3′,5′-cyclic phosphate (4, 9, 10, 11, 13) respectively and 6-chloro-9-β-D-ribofuranosylpurin-8-one 3′,5′-cyclic phosphate ( 5 ) and 8-amino-9-β-D-ribofuranosylpurine-6-thione 3′,5′-cyclic phosphate ( 6 ). The order of substitution was compared to similar substitutions on 6,8-dichloropurines and 6,8-dichloropurine nucleosides. The second scheme utilized nucleophilic substitution of 6-chloro-8-substituted-9-β-D-ribofuranosylpurine 3′,5′-cyclic, phosphates obtained from the corresponding 8-subslituted inosine 3′,5′-cyclic phosphates by phosphoryl chloride, 6,8-bis-(benzylthio)-, 6-(diethylamino)-8-(benzylthio),8-(p-chlorophenylthio(-6-(diethylamino)- and 6,8-bis-(methyl-thio)-9-β-D-ribofuranosylpurine 3′,5′-cyclic phosphates ( 14, 12, 20 , and 21 ) respectively, were prepared in this manner. The final scheme involved N¹-alkylation of an 8-substituted adenosine 3′,5′-cyclic phosphate followed by a Dimroth rearrangement to give 6-(benzylamino)-8-(methylthio)- and 6-(benzylamino)-8-bromo-9-β-D-ribofuranosylpurine 3′,5′-cyclic phosphate ( 24 and 25 ).