The quantum efficiency of the primary processes in formaldehyde photolysis at 3130 Å and 25°C

The mechanism of the photolysis of formaldehyde was studied in experiments at 3130 Å and in the pressure range of 1–12 torr at 25°C. The experiments were designed to establish the quantum yields of the primary decomposition steps (1) and (2), CH₂O + hν → H + HCO (1): CH₂O + hν → H₂ + CO (2), through the effects of added isobutene, trimethylsilane, and nitric oxide on Φ_CO and Φ. The ratio Φ_CO/Φ was found to be 1.01 ± 0.09(2σ) and (Φ + Φ_CO)/2 = 1.10 ± 0.08 over the range of pressures and a 12-fold change in incident light intensity. Isobutene and nitric oxide additions reduced Φ to about the same limiting value, 0.32 ± 0.03 and 0.34 ± 0.04, respectively, but these added gases differed in their effects on Φ_CO. With isobutene addition Φ_CO/Φ reached a limiting value of 2.3; with NO addition Φ_CO exceeded unity. The addition of small amounts of Me₃SiH reduced Φ to 1.02 ± 0.08 and lowered Φ_CO to 0.7. These findings were rationalized in terms of a mechanism in which the “nonscavengeable,” molecular hydrogen is formed in reaction (2) with ?₂ = 0.32 ± 0.03, while the “free radical” hydrogen is formed in reaction (1) with ?₁ = 0.68 ± 0.03. In the pure formaldehyde system these reactions are followed by (3)–(5): H + CH₂O → H₂ + HCO (3); 2HCO → CH₂O + CO (4); 2HCO → H₂ + 2CO (5). The data suggest k₄/k₅ ? 5.8. Isobutene reduced Φ by the reaction H + iso-C₄H₈ → C₄H₉ (20), and the results give k₂₀/k₃ ? 43 ± 4, in good agreement with the ratio of the reported values of the individual constants k₃ and k₂₀.     

Chemical actinometry at 147.0 nm

Hexafluoroacetone (HFA) and O₂ were photolyzed at 147.0 nm to investigate their use in chemical actinometry. The products, CO for the former and O₃ in the latter case, were monitored. For accurate comparison, both of these substances were irradiated by a single light source with two identical reaction cells at 180° to each other. The light intensities I were measured under the same integrated as well as instantaneous photon flux based on ? and ?_CO (quantum yield) as 2 and 1, respectively. Optimum conditions for maximum product yield were 5.0 torr HFA pressure and an O₂ flow rate of 200 ml/min at 1 atm pressure for a 20-minute photolysis period. For light intensity variations between 1.09 × 10¹⁴ and 2.10 × 10¹⁵ photons absorbed/sec, the ratio I/I_HFA was found to be unity. Calibration with the commonly used N₂O actinometer for a ? value of 1.41 showed that I/I_HFA and I/I are unity. Both HFA and O₂ are suitable chemical actinometers at 147.0 nm with ?_CO and ? of 1 and 2, respectively. The light intensity determination in the first case involves the measurement of only one product which is noncondensible at 77°K, whereas wet analysis for O₃, the only product, in the second actinometer is necessary. Both of these determinations are quite simple and are preferable over product analysis in N₂O actiometry, wherein N₂ separation from other noncondensibles at 77°K is required.     

Peculiar kinetics of the complex formation in the iron(III)–sulfate system

The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO₄), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH²⁺ (=FeH_?1), (FeOH) (=Fe₂H_?2), FeSO, and Fe(SO₄) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k_1a = 4.4 × 10³ M^?1 s^?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO₄), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH²⁺ (=FeH_?1), (FeOH) (=Fe₂H_?2), FeSO, and Fe(SO₄) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k_1a = 4.4 × 10³ M^?1 s^?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+$ step and k₂ = 1.1 × 10³ M^?1 s^?1 for the ${\rm FeSO}_4^+ + {\rm SO}_4^{2-} \stackrel{k_2}{\rightleftharpoons}\, {\rm Fe}({\rm SO}_4)_2^-$ step. The mono‐sulfate complex is also formed in the ${\rm Fe}({\rm OH})^{2+} + {\rm SO}_4^{2-} \stackrel{k_{1b}}{\longrightarrow} {\rm FeSO}_4^+$ reaction with the k_1b = 2.7 × 10⁵ M^?1 s^?1 rate constant. The most surprising result is, however, that the 2 FeSO? Fe³⁺ + Fe(SO₄) equilibrium is established well before the system as a whole reaches its equilibrium state, and the main path of the formation of Fe(SO₄) is the above fast (on the stopped flow scale) equilibrium process. The use and advantages of our recently elaborated programs for the evaluation of equilibrium and kinetic experiments are briefly outlined. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 114–124, 2008     

Unusual H2-forming chain reaction in the 3130-Å photolysis of formaldehyde-oxygen mixtures at 25°C

A kinetic study has been made of the 3130-Å photolysis of CH₂O (8 torr) in O₂-containing mixtures (0.02–8 torr) and in the presence of added CO₂ (0–300 torr) at 25°C. Quantum yields of formation of H₂, CO, and CO₂ and the loss of O₂ were measured. Φ and Φ_CO were much above unity. In an explanation of these unexpected results, a new H-atom-forming chain mechanism was postulated involving HO₂ and HO addition to CH₂O: CH₂O + hν → H + HCO (1) H + CH₂O → H₂ + HCO (3) H + O₂ + M → HO₂ + M (6) HCO + O₂ → HO₂ + CO (8) HO₂ + CH₂O → (HO₂CH₂O) → HO + HCO₂H (15) HO + CH₂O → H₂O + HCO? (16); HCO? → H + CO (19) HO + CH₂O → H₂O + HCO (17) and HO + CH₂O → HCO₂H + H (18). When the results are rationalized in terms of this mechanism, the data suggest k₁₆ ? k₁₇ and k₁₆/k₁₈ ? 0.5. The data require that a reassessment of the relative rates of reactions (7) and (8) be made, since in the previous work HCO₂H formation was used as a monitor of the rate of reaction (7) HCO + O₂ + M → HCOO₂ + M (7). The present data from experiments at P = 8 torr and P = 1–4 torr give k₇[M]/(k₇[M] + k₈) ≥ 0.049 ± 0.017. These data coupled with the k₈ estimates of Washida and coworkers give k₇ ≥ (4.4 ± 1.6) × 10¹¹ l²/mol²·sec for M = CH₂O. The reaction sequence proposed here is consistent with the observed deterimental effect of O₂ addition on the laser-induced isotope enrichment in HDCO. In additional studies of CH₂O-O₂-isobutene mixtures it was found that Φ was equal to ?₂ as estimated in O₂-free CH₂O-isobutene mixtures. These results suggest that the increase in CO (ν = 1) product observed with O₂ addition in CH₂O photolysis does not result from perturbations in the fragmentation pattern of the excited CH₂O, but it is likely that it originates in the occurrence of the exothermic reaction HCO + O₂ → HO₂ + CO (ν = 1).     

The mechanism of O(3P) atom reaction with ethylene and other simple olefins

Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10^?13cm³s^?1,K = (4.3 ± 0.4) ± 10^?12 cm³ s^?1, K = (1.4 ± 0.4) · 10^?11 cm³ s^?1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H-atom elimination was found for the reaction of O-atoms with 2-butene. A redistribution of reaction O + C₂ channels with pressure was found. A mechanism of the O + C₂ reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C₂ was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr.     

Reactivity of dpph• in the oxidation of catechol and catechin

A kinetic study of the reduction of pyrocatechol and catechin by dpph^? radical has been carried out in various ratios of CH₃OH/H₂O mixed solvent at pH 5.5–7.5, μ = 0.10 M [(n‐Bu)₄N]ClO₄, and T = 25°C. The rate constants of oxidation in aqueous solvent, k, were obtained from the extrapolation of the linear plots of the specific rate constants k vs. % H₂O plots at each pH value. A linear relationship between k and 1/[H⁺] was observed for both flavonoids with k = k₁K_a1/[H⁺], where K_a1 was the first acid dissociation constant on the catechol ring and k₁ is the rate constant of the oxidation of the mononegative species HX^?. The values of k₁ obtained from the slopes of the plots are (8.2 ± 0.2) × 10⁵ and (6.1 ± 0.1) × 10⁵ M^?1 s^?1 for pyrocatechol and catechin, respectively. The analysis of the reaction on the basis of Marcus theory for an outer‐sphere electron transfer reaction yielded a value of 3.7 × 10³ M^?1 s^?1 for the self‐exchange rate constant of dpph^?/dpphH couple. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 147–153, 2011     

The kinetics of the reaction F + H2 → HF + H. A critical review of literature data

Published experimental studies concerning the determination of rate constants for the reaction F + H₂ → HF + H are reviewed critically and conclusions are presented as to the most accurate results available. Based on these results, the recommended Arrhenius expression for the temperature range 190–376 K is k = (1.1 ± 0.1) × 10⁻¹⁰ exp |-(450 ± 50)/T| cm³ molecule⁻¹ s⁻¹, and the recommended value for the rate constant at 298 K is k = (2.43 ± 0.15) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The recommended Arrhenius expression for the reaction F + D₂ → DF + D, for the same temperature range, based on the recommended expression for k and accurate results for the kinetic isotope effect k/k is k = (1.06 ± 0.12) × 10^×10 exp |-(635 ± 55)/T|cm³ molecule⁻¹ s⁻¹, and the recommended value for 298 K is k = (1.25 ± 0.10) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 67–71, 1997.     

2–Butoxyethanol and benzyl alcohol reactions with the nitrate radical: Rate coefficients and gas‐phase products

The bimolecular rate coefficients k and k were measured using the relative rate technique at (297 ± 3) K and 1 atmosphere total pressure. Values of (2.7 ± 0.7) and (4.0 ± 1.0) × 10^?15 cm³ molecule^?1 s^?1 were observed for k and k, respectively. In addition, the products of 2‐butoxyethanol + NO₃^? and benzyl alcohol + NO₃^? gas‐phase reactions were investigated. Derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine and N, O‐bis (trimethylsilyl)trifluoroacetamide and gas chromatography mass spectrometry (GC/MS) were used to identify the reaction products. For 2‐butoxyethanol + NO₃^? reaction: hydroxyacetaldehyde, 3‐hydroxypropanal, 4‐hydroxybutanal, butoxyacetaldehyde, and 4‐(2‐oxoethoxy)butan‐2‐yl nitrate were the derivatized products observed. For the benzyl alcohol + NO₃^? reaction: benzaldehyde ((C₆H₅)C(?O)H) was the only derivatized product observed. Negative chemical ionization was used to identify the following nitrate products: [(2‐butoxyethoxy)(oxido)amino]oxidanide and benzyl nitrate, for 2‐butoxyethanol + NO₃^? and benzyl alcohol + NO₃^?, respectively. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with a plausible 2‐butoxyethanol or benzyl alcohol + NO₃^? reaction mechanisms based on previously published volatile organic compound + NO₃^? gas‐phase mechanisms. © 2012 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

© 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 778–788, 2012     

Kinetics and mechanism of the gas-phase thermal reaction between bis(fluoroxy) difluoromethane CF2(OF)2 and carbon monoxide

The kinetics of the gas-phase thermal reaction between CF₂(OF)₂ and CO has been studied in a static system at temperatures ranging between 110 and 140°C. The only reaction products were CF₂O and CO₂, giving the following stoichiometry: The reaction is homogeneous. The rate is strictly second order in CF₂(OF)₂ and CO, and is not affected by the total pressure or by the presence of reaction products. Oxygen promotes a sensitized oxidation of CO and inhibits the formation of CF₂O. The experimental results in the absence of oxygen can be explained by a chain mechanism similar to that proposed for the reaction between F₂O and CO with an overall rate constant of From the experimental data obtained on the oxygen-inhibited reaction, the rate constant for the primary process can be calculated: The chain length v = 2.5 is independent of the temperature. Taking for collision diameters σ = 6 Å and σ_CO = 3.74 Å, a value α = 5.3 × 10^?3 for the steric factor is obtained.     

Kinetics of oxidation of benzyl alcohol by sodium N-chloro-p-toluenesulfonamide

The kinetics of oxidation of benzyl alcohol and substituted benzyl alcohols by sodium N-chloro-p-toluenesulfonamide (chloramine-T, CAT) in HClO₄ (0.1–1 mol/dm³) containing Cl^? ions, over the temperature range of 30–50°C have been studied. The reaction is of first order each with respect to alcohol and oxidant. The fractional order dependence of the rate on the concentrations of H⁺ and Cl^? suggests a complex formation between RNCl^? and HCl. In higher acidic chloride solution the rate of reaction is proportional to the concentrations of both H⁺ and Cl^7hyphen;. The observed solvent isotope effect (k/k) is 1.43 at 30°C. The reaction constant (p = ?1.66) and thermodynamic parameters are evaluated. Rate expressions and probable mechanisms for the observed kinetics have been suggested.     

Iron carburization in CO‐H2‐He gases,Part II: Numerical model

A numerical model for the carburization of iron in CO‐H₂‐He mixtures was developed and compared with experimental data over the temperature range of 850°C–1150°C, CO partial pressures from 1% to 12%, and H₂ partial pressures from 5% to 99%. The reaction mechanism was established on the basis of data input from recent quantum mechanical and molecular dynamics calculations as well as from rate constant estimates from kinetic and transition state theory. Sensitivity and reaction flux analyses were performed to identify the rate‐controlling and fastest reactions. Model predictions of carbon weight gain in iron samples versus time were compared with experimental data. The most sensitive reactions were refined by least‐squares fitting the model to the experiment. The resulting model can simulate and predict the trends of iron carburization in CO‐H₂‐He‐CO₂‐H₂O mixtures for most conditions studied experimentally. Critical reactions and model parameters are identified for additional study to improve the model and understanding of the carburization mechanism. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 337–348, 2009     

The 13C and D kinetic isotope effects in the reaction of CH4 with Cl

The kinetic isotope effects in the reaction of methane (CH₄) with Cl atoms are studied in a relative rate experiment at 298 ± 2 K and 1013 ± 10 mbar. The reaction rates of ¹³CH₄, ¹²CH₃D, ¹²CH₂D₂, ¹²CHD₃, and ¹²CD₄ with Cl radicals are measured relative to ¹²CH₄ in a smog chamber using long path FTIR detection. The experimental data are analyzed with a nonlinear least squares spectral fitting method using measured high‐resolution spectra as well as cross sections from the HITRAN database. The relative reaction rates of ¹²CH₄, ¹³CH₄, ¹²CH₃D, ¹²CH₂D₂, ¹²CHD₃, and ¹²CD₄ with Cl are determined as k/k = 1.06 ± 0.01, k/k = 1.47 ± 0.03, k/k = 2.45 ± 0.05, k/k = 4.7 ± 0.1, k/k = 14.7 ± 0.3. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 110–118, 2005     

Solubility and hydrolysis of HCFC‐22 (CHF2Cl): Upward revision of rate constants for aqueous reactions of CHF2Cl with OH− at elevated temperature

Henry's law constants of CHF₂Cl in water at temperature T in K, K_H(T) in M atm^?1, were determined to be ln(K_H(T))=?(11.1±1.5)+((2290±500)/T) at 313–363 K by means of a phase ratio variation headspace method. The temperature‐dependent rate constants for aqueous reactions of CHF₂Cl with OH^?, k(T) in M^?1 s^?1, were also determined to be 3.7×10¹³exp(?(11, 200/T)) at 313–353 K, by considering the gas–water equilibrium, the aqueous reaction at room temperature, and liquid‐phase diffusion control. The liquid‐phase diffusion control was approximated with a one‐dimensional diffusion first‐order irreversible chemical reaction model. The k(T) value we determined is 10 times (at 353 K) or 3 times (at 313 K) as large as the value reported (R. C. Downing, Fluorocarbon Refrigerants Handbook, Prentice Hall: Englewood Cliffs, NJ, 1988). This upward revision of k(T) indicates that the removal efficiency of CHF₂Cl directly through the hydrolysis (CHF₂Cl + OH^?) is higher than previously expected at temperatures, such as 353 K, relevant to wet flue gas cleaning systems for ozone‐destruction substance‐destruction facilities. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 639–647, 2011     

Rate constants for the gas‐phase reactions of nitrate radicals with geraniol,citronellol, and dihydromyrcenol

Terpenes and terpene alcohols are prevalent compounds found in a wide variety of consumer products including soaps, flavorings, perfumes, and air fresheners used in the indoor environment. Knowing the reaction rate of these chemicals with the nitrate radical is an important factor in determining their fate indoors. In this study, the bimolecular rate constants of k (16.6 ± 4.2) × 10^?12, k (12.1 ± 3) × 10^?12, and k (2.3 ± 0.6) × 10^?14 cm³ molecule^?1 s^?1 were measured using the relative rate technique for the reaction of the nitrate radical (NO₃?) with 2,6‐dimethyl‐2,6‐octadien‐8‐ol (geraniol), 3,7‐dimethyl‐6‐octen‐1‐ol (citronellol), and 2,6‐dimethyl‐7‐octen‐2‐ol (dihydromyrcenol) at (297 ± 3) K and 1 atmosphere total pressure. Using the geraniol, citronellol, or dihydromyrcenol + NO₃? rate constants reported here, pseudo‐first‐order rate lifetimes (k′) of 1.5, 1.1, and 0.002 h^?1 were determined, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 669–675, 2010     

Gas‐phase reaction of Cl with dimethyl sulfide: Temperature and oxygen partial pressure dependence of the rate coefficient

The kinetics of the reaction of Cl atoms with dimethyl sulfide has been investigated using a relative rate technique. Experiments were performed with oxygen partial pressures of 0, 200, and 500 mbar at a total pressure of 1000 mbar (N₂ + O₂) over the temperature range 283–308 K in a 1080 L reactor using long path in situ Fourier transform infrared absorption spectroscopy to monitor the reactants. The 254 nm photolysis of trichloroacetyl chloride was used as the Cl atom source. Three reference hydrocarbons, cyclohexane, n‐butane, and propene were employed. Good agreement was found between the rate coefficients determined using the different reference compounds. The rate coefficients were found to decrease with increasing temperature at constant O₂ pressure and increase moderately with increasing O₂ partial pressure at constant temperature. The temperature dependences of the Cl atom reaction with dimethyl sulfide for the three O₂ partial pressure investigated can be expressed by the simple Arrhenius expressions: k = (4.22 ± 1.78) × 10^?13 exp((1968 ± 379)/T), k = (5.42 ± 1.85) × 10^?13 exp((1946 ± 381)/T), and k = (6.90 ± 2.04) × 10^?13 exp((1912 ± 381)/T). The errors are a combination of the 2σ statistical errors from the kinetic data analysis plus an estimated systematic error that includes the error in the reference hydrocarbon. The mechanistic implications of the results are discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 66–73, 2005     

Kinetics and mechanism of the oxidation of some carboxylates by a nickel (III) oxime-imine complex

The kinetics of the oxidation of formate, oxalate, and malonate by |Ni^III(L¹)|²⁺ (where HL¹ = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) were carried out over the regions pH 3.0–5.75, 2.80–5.50, and 2.50–7.58, respectively, at constant ionic strength and temperature 40°C. All the reactions are overall second-order with first-order on both the oxidant and reductant. A general rate law is given as - d/dt|Ni^III(L¹)²⁺| = k_obs|Ni^III(L¹)²⁺| = (k_d + nk_s |R|)|Ni^III(L¹)²⁺|, where k_d is the auto-decomposition rate constant of the complex, k_s is the electron transfer rate constant, n is the stoichiometric factor, and R is either formate, oxalate, or malonate. The reactivity of all the reacting species of the reductants in solution were evaluated choosing suitable pH regions. The reactivity orders are: k_HCOOH > k; k > k > k, and k > k < k for the oxidation of formate, oxalate, and malonate, respectively, and these trends were explained considering the effect of hydrogen bonded adduct formation and thermodynamic potential. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 225–230, 1997.     

Kinetics and mechanisms of substitution reactions with sulfur-containing nucleophiles in aqueous acid solutions. I—rates of reactions of some tetrahalopalladate (II) anions with thiourea and selenourea

The activation energy parameters for the reaction of PdX (X=Cl^?, Br^?) in aqueous halide acid solution with thiourea (tu) and selenourea (seu) have been determined. High rates of reaction parallel low enthalpies and appreciable negative entropy of activation. The rate law in each case simplifies to k_obs=k[L] where L=tu or seu, and only ligand-dependent rate constants are observed at 25°C. The ligand-dependent rate constants for the first identifiable step in the PdCl + X system is (9.1±0.1) × 10³ M^?1 sec^?1 and (4.5±0.1) × 10⁴ M^?1 sec^?1 for X=tu and seu, respectively, while for the PdBr + X system it is (2.0±0.1) × 10⁴ M^?1 sec^?1 and (9.0±0.1) × 10⁴ M^?1 sec^?1 for X=tu and seu, respectively.     

The reaction of methyl p-nitrophenyl sulfate with hydrogen peroxide anion determination of pKa of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure

A kinetic spectrophotometric investigation of the reaction of the hydrogen peroxide anion with methyl p-nitrophenyl sulfate in methanol solvent resulted in the evaluation of the pK_a of HOOH in methanol at 25°C as 15.8 ± 0.2. Since normal kinetic procedures for the determination of the equilibrium constant K for the process CH₃O^? + H₂O₂ ? CH₃OH + HO were found to be associated with high uncertainty, another procedure was devised to establish the magnitude of K. This method is based on an analysis of the changing slopes of plots of pseudo-first-order rate constants against the total base concentration as the stoichiometric amount of hydrogen peroxide is varied. The method is applicable to any system in which anionic nucleophiles generated in situ compete with solvent anions. Such a corroboration of kinetically determined equilibrium constants is believed essential. The kinetic data allow the specific rate constant k_HOO-for the reaction of methyl p-nitrophenyl sulfate with hydrogen peroxide anions to be evaluated and yield the rate constant ratio k/k = 8.8 ± 2.2. This confirms the existence of an α effect at saturated carbon in this system.     

Kinetic study of the interaction of adenosine 5′‐monophosphate with diaqua (2‐hydrazinopyridine) palladium(II) in aqueous medium

The interaction of the palladium(II) complex [Pd(hzpy)(H₂O)₂]²⁺, where hzpy is 2‐hydrazinopyridine, with purine nucleoside adenosine 5′‐monophosphate (5′‐AMP) was studied kinetically under pseudo‐first‐order conditions, using stopped‐flow techniques. The reaction was found to take place in two consecutive reaction steps, which are both dependent on the actual 5′‐AMP concentration. The activation parameters for the two reaction steps, i.e. ΔH = 32 ±2 kJ mol^?1, ΔS = ?168 ±7 J K^?1 mol^?1, and ΔH = 28 ± 1 kJ mol^?1, ΔS = ?126 ± 5 J K^?1 mol^?1, respectively, were evaluated and suggested an associative mode of activation for both substitution processes. The stability constants and the associated speciation diagram of the complexes were also determined potentiometrically. The isolated solid complex was characterized by C, H, and N elemental analyses, IR, magnetic, and molar conductance measurements. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 132–142, 2010     

The photochemistry of sulfur dioxide excited within its first allowed band (3130 Å) and the “forbidden” band (3700–;4000 Å)

The quantum yields of SO₃ formation have been determined in pure SO₂ and in SO₂ mixtures with NO, CO₂, and O₂ using both flow and static systems. In separate series of experiments excitation of SO₂ was effected within the forbidden band, SO₂(³B₁) ← \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm SO}_2 (\tilde X,^1 A_1 ) $$\end{document}, and within the first allowed singlet band at 3130 Å. The values of Φ were found to be sensitive to the flow rate of the reactants. These results and the apparently divergent quantum yield results of Cox [10], Allen and coworkers [24, 26, 29], and Okuda and coworkers [11] were rationalized quantitatively in terms of the significant occurrence of the reactions SO + SO₃ → 2SO₂ (2), and 2SO → SO₂ + S [or (SO)₂] (3), in experiments of long residence time. From the present rate data, values of the rate constants were estimated, k₂=(1.2±0.7) × 10⁶; k₃=(5±4) × 10⁵ l˙/mole · sec. Φ values from triplet excitation experiments at high flow rates of NO? SO₂ and CO₂? SO₂ mixtures showed the sole reactant with SO₂ leading to SO₃ formation in this system to be SO₂(³B₁); SO₂(³B₁) + SO₂ → SO₃ + SO(³Σ^?) (la); k=(4.2±0.4) × 10⁷ l./mole · sec. With excitation of SO₂ at 3130 Å both singlet and triplet excited states play a role in SO₃ formation. If the reactive singlet state is ¹B₁, the long-lived fluorescent state, SO₂(¹B₁) + SO₂ → SO₃ + SO (¹ Δ or ³Σ^?) (lb), then k=(2.2±0.5) × 10⁹ l./mole · sec. From the observed inhibition of SO formation by added nitric oxide, it was found that the SO₃-forming triplet state, generated in this singlet excited SO₂ system, had a relative reactivity toward SO₂ and NO which was equal within the experimental error to that observed here for the SO₂(³B₁) species. Either SO₂(³B₁) molecules were created with an unexpectedly high efficiency in 3130 Å excited SO₂(¹B₁) quenching collisions, or another reactive triplet (presumably ³A₂ or ³B₂) of almost identical reactivity to SO₂(³B₁) was important here.