Analytical capabilities of the microwave-coupled hollow-cathode discharge in emission spectroscopy

The intensity of spectra emitted by hollow copper cathodes with and without the superposition of 2450-MHz microwaves was studied under different operating conditions with argon as the filler gas. The hollow-cathode discharge was operated at 25–200 mA, with argon pressures ranging from 166 to 690 Pa. The intensities of the copper spectral lines are usually higher in the presence of microwaves, whereas the argon lines are weaker. The differences in the copper spectral lines with and without microwaves increase with increasing pressure of the filler gas and decreasing current. Analogous conclusions were reached for aqueous solutions of gold and silver ions placed in the cathode cavity and dried prior to discharge. The suitability of the method for improving the detection limits obtainable with the hollow-cathode discharge could thus be demonstrated.     

The removal of low level inorganics via electrogenerated hydrogen peroxide in the presence of catalytic amounts of Fe2+

Low level phosphites and hypophosphites were completely converted into phosphates, via hydrogen peroxide generated by cathodic reduction of oxygen in acidic aqueous medium at a reticulated vitreous carbon electrode, in the presence of little amounts of Fe2+. The contemporary regeneration of Fe2+ by cathodic reduction of Fe3+, produced by the well known Fenton reaction, furnishes an excellent way to continuously produce little amounts of the Fenton reactive and, as a consequence, of the powerful oxidant hydroxyl radical HO.. The best conditions for the complete removal of phosphorous as phosphites and hypophosphites are reported.     

Low temperature kinetics, crossed beam dynamics and theoretical studies of the reaction S((1)D) + CH4 and low temperature kinetics of S((1)D) + C2H2

The reaction between sulfur atoms in the first electronically excited state, S((1)D), and methane (CH(4)), has been investigated in a complementary fashion in (a) crossed-beam dynamics experiments with mass spectrometric detection and time-of-flight (TOF) analysis at two collision energies (30.4 and 33.6 kJ mol(-1)), (b) low temperature kinetics experiments ranging from 298 K down to 23 K, and (c) electronic structure calculations of stationary points and product energetics on the CH(4)S singlet potential energy surface. The rate coefficients for total loss of S((1)D) are found to be very large (ca. 2 × 10(-10) cm(3) molec(-1) s(-1)) down to very low temperatures indicating that the overall reaction is barrier-less. Similar measurements are also performed for S((1)D) + C(2)H(2), and also for this system the rate coefficients are found to be very large (ca. 3 × 10(-10) cm(3) molec(-1) s(-1)) down to very low temperatures. From laboratory angular and TOF distributions at different product masses for the reaction S((1)D) + CH(4), it is found that the only open reaction channel at the investigated collision energies is that leading to SH + CH(3). The product angular, T(θ), and translational energy, P(E'(T)), distributions in the center-of-mass frame are derived. The reaction dynamics are discussed in terms of two different micromechanisms: a dominant long-lived complex mechanism at small and intermediate impact parameters with a strongly polarized T(θ), and a direct pickup-type (stripping) mechanism occurring at large impact parameters with a strongly forward peaked T(θ). Interpretation of the experimental results on the S((1)D) + CH(4) reaction kinetics and dynamics is assisted by high-level theoretical calculations on the CH(4)S singlet potential energy surface. The dynamics of the SH + CH(3) forming channel are compared with those of the corresponding channel (leading to OH + CH(3)) in the related O((1)D) + CH(4) reaction, previously investigated in crossed-beams in other laboratories at comparable collision energies. The possible astrophysical relevance of S((1)D) reactions with hydrocarbons, especially in the chemistry of cometary comae, is discussed.