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A kinetic study of the reaction Na + O2 + He -> NaO2 + He has been carried out in a fast-flow reactor in the temperature and pressure ranges of, respectively, 392-777 K and 4-14 Torr.Sodium atoms are generated either by thermal evaporation of sodium metal or by the technique of microwave-induced plasma afterglow atomization.Atomic absorption spectroscopy is used as the detection technique for atomic sodium.A fit of k2 to the expression A(T/300)n yields k2 = (8.6 +/- 0.7)*10-31 (T/300)-1.04 +/- 0.16 cm6 molecule-2 s-1.This rate expression will be compared with kinetic data derived for the above reaction on the basis of time-resolved flash photolysis and excimer laser photolysis measurements.Using the Troe formalism, values of k2 are calculated in the temperature range 200-2000 K and the importance of the reaction in the burnt-gas region of oxygen-rich flames is discussed.

A fast flow reactor, with an oven source and resonant fluorescence detection, was used to study the kinetics of Na atoms in the gas phase.The rate constant for Na + O3 is (7.3+/-1.4)X10-10 cm3 molecule-1 s-1 at 286 K and NaO + O2 is the predominant product channel.The rate constant for Na + N2O over the temperature range 240 to 429 K is (3.7+/-0.9)X10-10exp cm3 molecule-1 s-1.The kinetics of the NaO radical were measured directly.NaO is made in the flow tube by the reaction Na + N2O -> NaO + N2 with N2O in large excess.NaO is detected by conversion to Na atoms in the detection region by NaO + NO -> Na + NO2.NaO + O3 has two exothermic product channels, Na + 2O2 and NaO2 + O2.The rate constants are ca. 5X10-11 and (1.8+/-0.4)X10-10 cm3 molecule-1 s-1 at 296 K, respectively.Upper limits for NaO + N2O -> Na + N2 + O2 and NaO + N2O -> NaO2 + N2 are 1X10-16 and 2X10-15 cm3 molecule-1 s-1, respectively.The rate constant for NaO + NO -> Na + NO2 is ca. 1.5X10-10 cm3 molecule-1 s-1.Since wall collisions remove Na0 with near unit efficiency, Na0 diffusion coefficients can be measured.DNaO,He = 640+/-340 cm2 Torr s-1 and DNaO,N2O = 48+/-24 cm2 Torr s-1 at 295 K.The error limits in all cases represent the 95percent confidence level, including an estimate of systematic errors.

The total sublimation pressure of Na2O(c) has been measured in the range 1000-1050 K by the torsion-effusion method, and the mass spectra of vapors over Na2O(c) and Na2O2(c) have been examined in order to resolve several issues regarding the thermochemical stability of the superoxide molecule NaO2.Measured torsion-effusion pressures are completely consistent with the primary sublimation process Na2O(c) = 2Na(g) + 0.5 O2(g) and set an upper limit of 200 kJ mol-1 for the bond strength D0(Na-O2).The ionization efficiency curves of Na+ and O2+ in the mass spectrumof vapor over Na2O(c) show no evidence for fragmentation contributions from NaO2.In addition, the absence of a detectable Na+/NaO2 fragment ion signal in vapor over Na2O2(c) can be used to derive an even tighter upper bound of 180 kJ mol-1 for D0(Na-O2).These results are in conflict with various kinetic analyses yielding D0(Na-O2) values of 202 to 243 kJ mol-1, but are in accord with rigorous theoretical calculations giving values near 160 kJ mol-1.

Measurements of sodium and OH concentrations in ten oxygen-rich H2/O2/N2 tlames by respective saturated and low-power laser-induced fluorescence techniques have led to a much improved understanding of the complex flame chemistry of sodium in such oxygen-rich media.Previous interpretations have been shown to be largely incomplete or infiniten error.The one-dimensional tlame downstream profiles indicate that the amount of free sodium approximately tracks the decay of H atom and as the tlame radicals decay sodium becomes increasingly bound in a molecular form.A detailed kinetic model indicates that the sodium is distributed between NaOH, which is dominant, and NaO2.Concentrations of NaO are very small and NaH negligible.The actual distribution is controlled by the temperature, the oxygen concentration, and the degree of nonequilibration of the flames' basic free radicals.Na, NaO, NaO2, and NaOH are all coupled to one another by fast reactions which can rapidly interconvert one to another as tlame conditions vary.NaOz plays an indispensable role in providing alternate efficient channels by which NaOH can be produced.Its contribution becomes increasingly important at lower temperatures where the tlux through the NaO2 intermediate becomes dominant over that for the direct reaction between Na and H2O.As a consequence, the ratio of NaOH to Na can become enhanced by up to two orders of magnitude at lower temperatures over what might have been expected from the Na + H2O direct reaction alone.The dissociation energy is established to be 39 +/- 5 kcal mol-1 and the value of the rate constant for the Na + O2 + M reaction of 2 X l0-28 T-1 cm6 molecule-2 s-1 for the tlame gases.The sodium distribution within the highest temperature, low-O2 flame, in which NaOH is dominant and equilibrated, supports a value of (Na-OH) of 78.9 +/- 2 kcal mol-1.The rate constants for several reactions of Na, NaOH, NaO2, and NaO with flame species have been established approximately.An analysis of the total kinetic scheme shows that the chemical fluxes are carried predominantly by four reactions only.These considered alone, reproduce the data surprisingly well.An analysis of the implications of the corresponding large rate constants for the termolecular reaction of the other alkali metals with oxygen saggests that these will undoubtedly show to varying degrees similar behavior to sodium.Values for the bond dissociation energies of the other alkali dioxides are discussed.It appears that in practical combustion systems, even at low temperatures, the conversion of alkali metals to the corresponding hydroxide will not be kinetically constrained and its concentration will be at or in excess of the expected equilibrium value.

The reaction of atomic sodium with ozone is important in describing the chemistry of the lower thermosphere and upper mesophere and is directly related to the observed sodium D line emissions at 589 nm in these regions of the atmosphere.A room temperature rate constant of this reaction is found to be (3.1 +/- 0.4)*E-10 cm3 molecule-1 s-1.The rate constant for the NaO + O3 reaction is determined to be about 2*E-10 cm3 molecule-1 s-1, with 0.7 +/- 0.2 of the products being NaO2 + O2 and the remainder Na + 2O2.Also measured is the rate constant for Na + N2O -> NaO + N2, found to be (7.7 +/- 0.9)*E-13 cm3 molecule-1 s-1 at 295 K.The impact of the reactions with ozone on the mesopheric chemistry of alkali metals of meteoric origin is discussed.

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The absolute cross section for the photodissociation process NaO2 + hν -> Na + O2 has been measured at 230 K by the technique of pulsed excimer laser photolysis of NaO2 followed by laser-induced fluorescence of the resulting Na fragment, yielding ?(193nm)

Recent evidence has shown that the mesospheric sodium nightglow, a chemiluminescent process which produces atomic sodium D-line radiation in the Earth's upper atmosphere, proceeds through the first excited (A 2∑+) electronic state of NaO. The rate of D-line radiation production is proportional to the rate constant for the reaction of NaO(A 2∑+) + O(3P) and its branching ratio to produce excited Na(2P) rather than ground-state Na(2S). The only previously published measurement of the NaO + O(3P) reaction rate and branching ratio was performed under slow flow conditions and almost certainly primarily represents the reaction of groundstate NaO (X 2∏). We present low-pressure measurements of the NaO + O reaction kinetics using an NaO source reaction known to produce NaO in the (A 2∑+) state and determine the 290 K reaction rate constant to be (5.1 ± 1.8) × 10-10 cm3 s-1 and the branching ratio to produce Na(2P) to be 0.14 0.04. New data on the termolecular rate coefficient for the reaction Na + O2 + He → NaO2 + He at 290 K are also presented.

The reduction of dioxygen in the presence of sodium cations can be tuned to give either sodium superoxide or sodium peroxide discharge products at the electrode surface. Control of the mechanistic direction of these processes may enhance the ability to tailor the energy density of sodium–oxygen batteries (NaO2: 1071 Wh kg?1and Na2O2: 1505 Wh kg?1). Through spectroelectrochemical analysis of a range of non-aqueous solvents, we describe the dependence of these processes on the electrolyte solvent and subsequent interactions formed between Na+and O2 ?. The solvents ability to form and remove [Na+-O2 ?]adsbased on Gutmann donor number influences the final discharge product and mechanism of the cell. Utilizing surface-enhanced Raman spectroscopy and electrochemical techniques, we demonstrate an analysis of the response of Na-O2cell chemistry with sulfoxide, amide, ether, and nitrile electrolyte solvents.

An adaptation of the HTP (high-temperature photochemistry) technique to make it suitable for the study of metal atoms is described.In this, the first such HTP work, sodium salts are evaporated and ground-state atomic Na is generated by pulsed excimer or flash lamp photolysis.The decay of under pseudo-first-order conditions in the presence of O2 is monitored by time-resolved resonance absorption at 589 nm and total N2 pressures from 40 to 320 mbar.For the reaction Na + O2 + N2 -> NaO2 + N2 (1), we thus determine log k (590-1515 K) = -44.29 + 11.70 log T -2.347 (log T)2 (cm6 molecule-2 s-1) with a 2? confidence interval of 21-26percent, depending on temperature, which figures include a liberal allowance for potential systematic errors.Agreement with other studies of reaction 1 in isolation, over more limited temperature ranges, is good in regions of overlapping temperatures, but simple empirical extrapolations of the various data sets deviate.Results of calculations based on a Troe formalism for energy transfer well describe the present and most of these previous k(T) determinations.No evidence of equilibration of reaction 1 is observed, from which we conclude that the bond energy D0(Na-O2) 230 +/- 5 kJ mol-1, in accord with a recent flame modeling study but not with the ab initio calculations presented.

Metal compounds originating from meteor ablation may provide an additional mechanism for the release of free chlorine from HCl in the stratosphere.For the alkali metals, and sodium in particular, catalytic chemical pathways have been postulated that describe these processes.A critical step in this mechanism is the reaction of NaO2 with HCl.The rate constant for this reaction has been measured in a fast-flow reactor at 295 K and found to be (2.3 +/- 0.4)*E-10 cm3 molecule-1 s-1.The implication of this result on stratospheric ozone chemistry is discussed.

An investigation is presented of the recombination reaction Na + O2 + N2 by the technique of pulsed photolysis of a Na atom precursor followed by time-resolved laser induced fluorescence spectroscopy of Na atoms at λ = 589 nm.Termolecular behavior was dem

Products of the gas-phase reactions M + N2O and M + O3, where M = Na or K, have been investigated with UV photoelectron spectroscopy and bands have been assigned with the assistance of results from ab initio molecular orbital calculations.For the M + N2O

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