Arthur Fontijn

Absolute Quantum Yield Measurements of the NO–O Reaction and Its Use as a Standard for Chemiluminescent Reactions

The spectral distribution of the chemiluminescent reactions O+NO→NO2+hv has been determined over the wavelength region 3875–14 000 A. The absolute rate constant was determined by a method of chemical actinometry which required only relative intensity measurements and which is virtually free from geometry errors. The rate constant over this spectral region was found to be 6.4×10—17 cm3 molecule—1 sec—1 within an accuracy of 30%. This reaction can be used as a standard from which the rate constants for other chemiluminescent reactions can be readily obtained without requiring detector calibration or geometry corrections.

High‐temperature photochemistry and BAC‐MP4 studies of the reaction between ground‐state H atoms and N2O

The H+N2O reaction has been investigated using the high‐temperature photochemistry (HTP) technique. H(1 2S) atoms were generated by flash photolysis of NH3 and monitored by time‐resolved atomic resonance fluorescence with pulse counting. The bimolecular rate coefficient for H‐atom consumption, leading essentially to N2+OH, from 390 to 1310 K is found to be given by k1(T)=5.5×10−14 exp(−2380 K/T)+7.3×10−10 exp(−9690 K/T) cm3 molecule−1 s−1; the accuracy is assessed as approximately 25% at the 2σ confidence level. Above 750 K, k1 closely follows the Arrhenius behavior of the second term alone. Distinct curvature is evident below 750 K. k1 is compared to theoretical BAC‐MP4 predictions and good agreement is found for a model involving rearrangement of an HNNO intermediate coupled with tunneling through an Eckart potential barrier, which dominates at the lower temperatures. The branching ratio for the channel leading to NH+NO is discussed in the context of recent thermochemical information and a maximum rate ...

HTFFR kinetics studies of Al+CO2→AlO+CO from 300 to 1900 K, a non‐Arrhenius reaction

High‐temperature fast‐flow reactors (HTFFR) were used to obtain the rate coefficients k1 (and their accuracies) for the reaction Al +CO2→AlO+CO. At 310, 490, 750, 1500, and 1880 K, k1 is found to be (1.5±0.6) ×10−13, (6.9±2.7) ×10−13, (1.6±0.7) ×10−12, (9.0±3.8) ×10−12, and (3.8±1.5) ×10−11, respectively (all in ml molecule−1 s−1 units). For this temperature range k1(T) may be expressed by the curve fitting equation k1(T) =2.5 ×10−13 T1/2 exp(−1030/T)+1.4×10−9 T1/2 exp(−14 000/T). The data also indicate a wall‐oxidation process of zeroth order in [CO2] with γAl of 10−3 to 10−2, not measurably dependent on T. Factors affecting the accuracy of the measurements are discussed. Over the 310–750 K range k1(T) obeys an Arrhenius expression, with an activation energy of 2.6±1.3 kcal mole−1, which implies D(Al–O) ?122 kcal mole−1. Above 750 K, k1(T) increases much more rapidly with T. This behavior cannot be described on the basis of simple transition state theory alone; the most probable additional factors involv...

Activation barriers for series of exothermic homologous reactions. I. Metal atom reactions with N2O

We recently observed that the activation barriers of O‐atom abstraction reactions between metal atoms and N2O, in which both reactants are in their ground electronic states and the atoms contain no valence p electrons, vary systematically with the sums of the metal atom ionization potential and the energy required to promote a valence s electron to the lowest p orbital. It is shown here that this observation can be explained by the assumption that the activated complex results from the resonance interactions of ionic and covalent structures. Activation barriers for 43 reactions are calculated and where experimental measurements are available, are shown to be in good agreement with those. New interpretations are offered for literature data on the Ca and Cr reactions. The resonance treatment leads to a more general relationship in which activation barriers depend simultaneously on ionization potentials, electron affinities, promotion energies, and bond energies of the reactants. A number of further series o...

Recent progress in chemi-ionization kinetics

A review of chemi-ionization reactions based on knowledge acquired since 1968 is given. Chemi-ionization reactions are considered to be: ‘Reactions by which the number of elementary charge carriers is increased as the direct result of the formation of new chemical bonds’. This includes both associative (A + B → AB + + e - ) and rearrangement (A + BC → AB + + C + e - ) ionization reactions. Rate coefficients for these reactions are often on the order of 10 12 to 10 -9 ml molecule -1 sec -1 and decrease with increasing temperature (relative collision velocity). For a given reactant A the rate coefficients also tend to decrease with an increasing number of atoms in B. A number of examples of exoergic chemi-ionization reactions between ground state reactants have now been definitely established. More detailed knowledge of reactions involving an electronically excited collision partner has become available and meaningful comparisons to Penning ionization can be made. However, our understanding of the details of the processes occurring are based primarily on observations of noble gas metastables, which, as is shown, do not in all respects apply to reactions of other species.

An HTP kinetics study of the reaction between ground‐state H atoms and NH3 from 500 to 1140 K

Article on an HTP kinetics study of the reaction between ground-state H atoms and NH₃ from 500 to 1140 K.

Mechanism of CO fourth positive v u v chemiluminescence in the atomic oxygen reaction with acetylene. Production of C(3P, 1D)

CO(A 1Π−X 1Σ) emission from the O/C2H2 reaction has been studied in a room temperature discharge flow system at pressures from 0.6 to 10 torr. Spectrometric measurements showed that CO(A 1Π) excitation extends to at least ν′ = 12, with anomalously large populations of the ν′ = 1, 4 and 6 levels. The overall emission intensity increases with increasing [Ar], [N2], and [He]. The presence of C(3P and 1D) atoms has been observed via resonance fluorescence. The probable CO(A 1Π)‐formation mechanism is O + C2O → CO* + CO, followed by collision‐induced cross relaxation: CO* + M → CO(A 1Π) + M, where CO* is identified as a CO state having a potential energy curve which overlaps that of CO(A 1Π), i.e., the d3Δ, e3Σ, a′3Σ and/or D1Δ states. The hypothetical reaction C + O + M → CO(A 1Π) + M does not populate CO(A 1Π) to a significant degree.

HTFFR kinetics studies of Sn/N2O, a highly efficient chemiluminescent reaction

High temperature fast‐flow reactors (HTFFR) were used to study the Sn/N2O reaction from 300–950 K at pressures from 4 to 110 Torr. The observed emissions are SnO[a 3Σ+(1) –X 1Σ+] and (b 3Π–X 1Σ+). The photon yield of the former system is 0.53±0.26 independent of T, that of the latter (5.9±2.9) ×10−1 exp[−(1200±200)/T]. Comparison of the photon yields of N2O‐ in‐excess experiments, where [Sn] is measured in absorption, to experiments where Sn is in excess allows determination of oscillator strengths for the ground electronic states of Sn: f[Sn(3P0) (286.4 nm)]=0.20±0.10 and f[Sn(3P1) (300.9 nm)]=0.052±0.026, in good agreement with literature values. At T≳950 K, emission from SnO(c–X 1Σ+) and (A 1Π–X 1Σ+) is observed, apparently due to N2O decomposition followed by Sn/O2 reaction. Quenching rate coefficients at ≈900 K for SnO (a) are determined to be kQN2(a)⩽2.3×10−16; kQAr(a)⩽4.0×10−16; kQN2O(a)⩽4.0×10−14; kQSn(a)⩽4.0×10−12 ml molecule−1 s−1 based on τrad(a)⩾2.5×10−4 s. For SnO (b) the data yield τbkQN2(b)...

Tubular Fast Flow Reactor for High Temperature Gas Kinetic Studies

A fast flow reactor suitable for gas kinetic studies at temperatures up to ≈2000 K is described. The reactor has been used in studies of the reactions of atomic Fe and Na with O2, for which performance data are given.

High-temperature fast-flow reactor study of Sn/N2O chemiluminescence

Abstract The Sn/N 2 O reaction at 1000 K produces intense chemiluminescence belonging to the A, B, C, D-X systems of SnO. The number of photons emitted per Sn atom reacted is on the order of 0.5. New A-X bands at λ ≫ 550 nm have been identified. The overall reaction proceeds with a rate coefficient of ≈ 5 × 10 −13 ml molecule −1 s −1 .