Quenching of N2(A3Σu+) by O2, O,N, and H

Metastable N₂(A³Σ_u⁺), υ = 0, υ = 1, molecules are produced by a pulsed Tesla-type discharge of a dilute N₂/Ar gas mixture. Rate coefficients for quenching these metastable levels by O₂, O, N, and H were obtained by time-resolved emission measurements of the (0, 6) and (1, 5) Vegard–Kaplan bands. In units of cm³/mole · sec at 300°K and with an experimental uncertainty of ±20%, these rate coefficients for N₂(A³Σu⁺) are Within the limits of error these coefficients apply to quenching N₂(A³Σ_u⁺) υ′ = 1 as well.     

Determination of chain stiffness and polydispersity from static light-scattering

Chain stiffness is often difficult to distinguish from molecular polydisperity. Both effects cause a downturn of the angular dependence at large q² (q = (4π/λ)sin θ/2) in a Zimm plot. A quick estimation of polydisperity becomes possible from a bending rod (BR) plot in which lim (c → 0) qRθ/Kc is plotted against q(〈S²〉_z)^1/2 = u. Flexible and semiflexible chains show a maximum whose position is shifted from u_max = 1.41 for monodisperse chains towards larger values as polydispersity is increased, while simultaneously, the maximum height is lowered. Stiff chains display a constant plateau at large q, its value is πM_L where M_L is the linear mass density. Using Koyama's theory, the number of Kuhn segments can be determined from the ratio of the maximum height to the plateau height, if the polydispersity index z = (M_w/M_n ? 1)^?1 is known. Thus, if the weight-average molecular weight M_w, is known, the contour length L_w, the number of Kuhn segments (N_k)_w, the Kuhn segment length l_k and the polydispersity of the stiff chains can be determined. The influence of excluded volume is shown to have no effect on this set of data. The reliability of this set can be cross-checked with the mean-square radius of gyration 〈s²〉_z which can be calculated from the Benoit-Doty equation for polydisperse chains. Rigid and slightly bending rods exhibit no maximum in the BR plot, and the effect of polydispersity can no longer be distinguished from a slight flexibility if only static scattering techniques are applied.     

The carbon–hydrogen bond strength in dimethyl ether and some properties of iodomethyl methyl ether

The kinetics and mechanism of the reaction between iodine and dimethyl ether (DME) have been studied spectrophotometrically from 515–630°K over the pressure ranges, I₂ 3.8–18.9 torr and DME 39.6–592 torr in a static system. The rate-determining step is, where k₁ is given by log (k₁/M^?1 sec^?1) = 11.5 ± 0.3 – 23.2 ± 0.7/θ, with θ = 2.303RT in kcal/mole. The ratio k₂/k_?1, is given by log (k₂/k_?1) = ?0.05 ± 0.19 + (0.9 ± 0.45)/θ, whence the carbon-hydrogen bond dissociation energy, DH° (H? CH₂OCH₃) = 93.3 ± 1 kcal/mole. From this, ΔH°_f(CH₂OCH₃) = ?2.8 kcal and DH°(CH₃? OCH₂) = 9.1 kcal/mole. Some nmr and uv spectral features of iodomethyl ether are reported.     

Explanation for the 3.4-power law for viscosity of polymeric liquids on the basis of the tube model

The viscosity η₀(M) of polymeric liquids of molecular weight M is calculated on the basis of the tube model formulated by Doi and Edwards (ref. 3). The contour length fluctuation of polymers along the tube, which was neglected in ref. 3, is now explicitly taken into account. The result is where M_c = 2M_e, and M_e is the molecular weight between the entanglement points. This result is numerically close to the empirical 3.4-power law, η₀(M) = η₀(M_c)(M/M_c)^3.4, for 10M_c ? M ? 100M_c but approaches the result in ref. 3 for very high molecular weight. We thus conclude that the 3.4-power law is actually an approximate expression for the real curve which slowly approaches the asymptotic form calculated in ref. 3.     

The kinetics of the interaction of peroxy radicals. I. The Tertiary Peroxy Radicals

Existing data on the self-reactions of tertiary peroxy radicals RO₂ has been reanalyzed and corrected to deduce Arrhenius parameters for both termination and nontermination paths. For R = t-Butyl, these are logk_t(M^?1sec^?1) = 7.1 - (7.0/θ) and logk_nt(M^?1sec^?1) = 9.4 - (9.0/θ), respectively, different from those recommended by other authors. The higher magnitudes observed for termination processes of tertiary peroxy radicals like those of cumyl and 1,1-diphenylethyl have been discussed in terms of a much greater cage recombination of cumyloxy radicals as contrasted with t-butoxy radicals. It is shown that for benzyl peroxy radicals, the R—O bond dissociation energy is sufficiently low (18–20 kcal) that reversible dissociation into R^˙ + O₂ opens a competing second-order path to fast recombination R^˙ + RO → ROOR. This path is probably not important for cumyl peroxy radicals under usual experimental conditions but can become important for 1,1-diphenyl ethyl peroxy radicals at (O₂) < 10^?3M. At very low RO concentrations (<10^?5M), in the absence of added O₂, an apparent first-order disappearance of RO can occur reflecting the rate determining breaking of the cumyl—O bond followed by the second step above. The thermochemistry of RO is used to show that the reaction of R₂O₄ → 2RO + O₂ must be concerted and cannot proceed via RO which is too unstable and cannot form even from RO^˙ + O₂.     

Crosslinking,filler, or transition constraint of polymer networks. I

The basic theory of modulus/swelling is developed to allow for limited extensibility, filler reinforcement or transition effects, and steric hindrance of aligned segments by extended chains or filler particles. Filler forms an effective hard fraction C_h per cubic centimeter of compound with v_c a new (compound) index of swelling. For 1/M_c + σ fix points having ratio φ to gum values 1/F₀(v_r) and with F(v_c) replacing the Flory function F(v_r): where σ denotes entanglement. Linkage reinforcement φ does not vary with sulfur crosslinking of SBR. Vacuoles invalidate φ from mass-increment F₀(v_r)/F(v_r) for inert fillers. Then, or for Graphon, with negligible φ ≈ 1: The effective C_h includes rubber stretched hard on Graphon by swelling or trapped inside hard aggregates. Only the right-hand equation fits normal blacks. In theory, C_h can always be obtained from swollen moduli G by linear slopes (1 + 1.4C_h) relating F(v_c) and (1 ? C)ρRT/G. For filler fractions C ≥ 0 cm^?3 and low strains α = 1.5?2.0 below prestretch the modulus G is given a new basic definition: Here C₂* ≈ 0.7 corresponds to Mooney-Rivlin C₂ and the effective crosslinking 1/[M_c] = (ρRT)^?1G is equal to (1 ? C)(1/M_c + σ) for unswollen prestretched rubber (v_r = 1). For higher strains a hypothesis of strain hardening is proposed. This is distinct and opposite in character to the initial prestretch softening (Mullins effect). Nonlinear effects of crosslinks are expressed by a fractional stress-upturn Ω (1/M_c + σ), effective mesh wieght (1/M_c + σ)^?1 ? Ω, and hard fraction Ω(1/M_c + σ). For μ_h characterizing strain hardening up to the prestretch (α_h ? 1) their contribution is: The sixth-power refinement has J = j(α_b ? 1)^1/2 with j ≈ 0.4. The hard phase is augmented by filler and grows with increasing strain up to the prestretch.     

TI(III) oxidation of alkenes and alkynes and Ru(III) catalysis in the oxidation of alkenes: A kinetic and mechanistic study

The oxidation of trans-stilbene, phenylacetylene, and diphenylacetylene by Tl(OAc)₃ in aqueous acetic acid medium in the presence of HClO₄ follows the rate law in [H⁺] of 0.1–1.0M, the [H⁺] dependence below 0.1M being marginal. The reactions are strongly dielectric dependent. The order of reactivity among the substrates is styrene > phenylacetylene and trans-stilbene > diphenylacetylene. A mechanism involving the oxythallation adduct by the Tl⁺(OAc)₂ species has been discussed. The use of Ru(III) as a homogeneous catalyst brings a change in the kinetic orders for trans-stilbene, the rate law being The formation constants K for the Ru(III)–alkene π complex at 40, 50, and 60°C are 90.14M^?1, 105.2M^?1, and 127.7M^?1, respectively. Interestingly the oxidation of phenylacetylene and diphenylacetylene does not undergo catalysis by Ru(III). The mechanism involving the metal–arene π complex is discussed.     

The decomposition of dimethyl peroxide and the rate constant for CH3O + O2 → CH2O + HO2

The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO₂ to determine rate constants k₁ and k₂ in the temperature range of 391–432°K: The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k₁(sec^?1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k₂ ≈ 5 × 10⁴M^?1· sec^?1. The disproportionation/recombination ratio k_7b/k_7a = 0.30 ± 0.05 was also determined: When O₂ was added to DMP mixtures containing NO₂, relative rate constants k₁₂/k_7a were obtained over the temperature range of 396–442°K: A review of literature data produced k_7a = 10^9.8±0.5M^?1·sec^?1, giving log k₁₂(M^?1·sec^?1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.     

Extraction of certain actinide and lanthanide elements from different acid media by polyurethane foams loaded with di(2-ethylhexyl)phosphoric acid (HDEHP)

Except for conditions of low acidity and low ratios of di(2-ethylhexyl)phosphoric acid (HDEHP) to U(VI) the data obtained for the distribution of U(VI) between sulfuric acid solutions and polyurethane foams loaded with solutions of HDEHP in nitrobenzene could be analyzed by the equation: log (4.36 D_u)=log K+1.43 log (C_d–4C_u)/(C_H)^1.4+log f_u where the polymerization number of HDEHP is about 2.8, D_u is the distribution ratio, and f_u=[UO ₂ ²⁺ ]_(aq)/[UO₂]_(aq) indicating that the extraction proceeds via the formation of a 14 UO₂:HDEHP complex. At both low acidity and HDEHP/U(VI) ratio a UO₂-HDEHP polymer is formed.     

Chain ion molecular mechanism of ascorbic acid oxidation with hydrogen peroxide. Cu3+ ion as a chain carrier

The kinetics and mechanism of ascorbic acid (DH₂) oxidation have been studied under anaerobic conditions in the presence of Cu²⁺ ions. At 10^?4 ≤ [Cu²⁺]₀ < 10^?3M, 10^?3 ≤ [DH₂]₀ < 10^?2M, 10^?2 ≤ [H₂O₂] ≤ 0.1M, 3 ≤ pH < 4, the following expression for the initial rate of ascorbic acid oxidation was obtained: where χ₂ (25°C) = (6.5 ± 0.6) × 10^?3 sec^?1. The effective activation energy is E₂ = 25 ± 1 kcal/mol. The chain mechanism of the reaction was established by addition of Cu⁺ acceptors (allyl alcohol and acetonitrile). The rate of the catalytic reaction is related to the rate of Cu⁺ initiation in the Cu²⁺ reaction with ascorbic acid by the expression where C is a function of pH and of H₂O₂ concentration. The rate equation where k₁(25°C) = (5.3 ± 1) × 10³M^?1 sec^?1 is true for the steady-state catalytic reaction. The Cu⁺ ion and a species, which undergoes acid–base and unimolecular conversions at the chain propagation step, are involved in quadratic chain termination. Ethanol and terbutanol do not affect the rate of the chain reaction at concentrations up to ≈0.3M. When the Cu²⁺–DH₂–H₂O₂ system is irradiated with UV light (λ = 313 nm), the rate of ascorbic acid oxidation increases by the value of the rate of the photochemical reaction in the absence of the catalyst. Hydroxyl radicals are not formed during the interaction of Cu⁺ with H₂O₂, and the chain mechanism of catalytic oxidation of ascorbic acid is quantitatively described by the following scheme. Initiation: Propagation: Termination:      

The very-low-pressure pyrolysis (VLPP) of n-propyl nitrate,tert-butyl nitrite,and methyl nitrite. Rate constants for some alkoxy radical reactions

The pyrolysis of n-propyl nitrate and tert-butyl nitrite at very low pressures (VLPP technique) is reported. For the reaction the high-pressure rate expression at 300°K, log k₁ (sec^?1) = 16.5 ? 40.0 kcal/mole/2.3 RT, is derived. The reaction was studied and the high-pressure parameters at 300°K are log k₂(sec^?1) = 15.8 ? 39.3 kcal/mole/2.3 RT. From ΔS_1,?1⁰ and ΔS_2,?2⁰ and the assumption E_?1 and E_?2 ? 0, we derive log k_?1(M^?1·sec^?1) (300°K) = 9.5 and log k_?2 (M^?1·sec^?1) (300°K) = 9.8. In contrast, the pyrolysis of methyl nitrite and methyl d₃ nitrite afford NO and HNO and DNO, respectively, in what appears to be a heterogeneous process. The values of k_?1 and k_?2 in conjunction with independent measurements imply a value at 300°K for of 3.5 × 10⁵ M^?1·sec^?1, which is two orders of magnitude greater than currently accepted values. In the high-pressure static pyrolysis of dimethyl peroxide in the presence of NO₂, the yield of methyl nitrate indicates that the combination of methoxy radicals with NO₂ is in the high-pressure limit at atmospheric pressure.     

Polymerization mechanisms and molecular weight distribution. I. Mathematical treatment

A novel method for determining the polymerization mechanism and the kinetic rate constants from the molecular weight distribution is proposed. The particular criterion function used as basis for parameter adjustment is where θ is the vector of dependent variables, y(r, θ) is the theoretical molecular weight distribution for the assumed polymerization mechanism, and y_E(r) is the experimental molecular weight distribution which is a function of the chain length r. A form of the gradient method of optimization was used to solve the criterion function. The proposed method is particularly powerful since the whole molecular weight distribution is utilized.     

Kinetics of the “a” and “b” band emissions of mercury excimers with added gases

The kinetics of the “a” and “b” band emissions arising from the ¹Σ ← ³O_u and ¹Σ ← ³l_u transitions of the diatomic mercury molecule at λ_max ～ 4850 Å and 3350 Å, respectively, have been studied at low concentrations of mercury in the presence of N₂, C₂H₆, C₃H₈, and N₂O. Rate constant values have been obtained for the following reactions of the excimer molecule: Hg₂(³l_u) + N₂ → Hg₂(³O_u) + N₂ and Hg₂(³O_u) + RH → Hg₂(¹Σ) + RH, where RH = C₂H₆ or C₃H₈. From a consideration of the detailed kinetics of band emissions, it was also possible to derive rate constants for the quenching reactions of Hg(³P₀) atoms. These values are in reasonable agreement with those obtained previously from monitoring atom concentrations directly by 4047 Å absorbiometry.     

The kinetics and mechanism of the oxidation of formic acid by bromine in acid aqueous media

The reaction between formic acid and bromine in strongly acid aqueous media at 298 K was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = -d[Br₂]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br₂[(2.7–13.6) × 10^?3M], H⁺ (0.03–2.0M), and Br^? (up to 0.6M). The mechanism with k₁ = 20.2 ± 1.2 M^?1 sec^?1, pK₂ = 3.76, pK₃ = ?1.20, accounts for all experimental observations. Br₃^? and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species.     

Shock tube study of cyanogen oxidation kinetics

Mixtures of cyanogen and nitrous oxide diluted in argon were shock-heated to measure the rate constants of A broad-band mercury lamp was used to measure CN in absorption at 388 nm [B²Σ⁺(v = 0) ← X²Σ⁺(v = 0)], and the spectral coincidence of a CO infrared absorption line [v(2 ← 1), J(37 ← 38)] with a CO laser line [v(6 → 5), J(15 → 16)] was exploited to monitor CO in absorption. The CO measurement established that reaction (3) produces CO in excited vibrational states. A computer fit of the experiments near 2000 K led to An additional measurement of NO via infrared absorption led to an estimate of the ratio k₅/k₆: with k₅/k₆ ? 10^3.36±0.27 at 2150 K. Mixtures of cyanogen and oxygen diluted in argon were shock heated to measure the rate constant of and the ratio k₅/k₆ by monitoring CN in absorption. We found near 2400 K: and The combined measurements of k₅/k₆ lead to k₅/k₆ ? 10^?3.07 exp(+31,800/T) (±60%) for 2150 ≤ T ≤ 2400 K.     

Exponentially generated wave functions and excited states of benzene

Usefulness of the exponentially generated wave function approach is shown. We first give an overview of the SAC (symmetry adapted cluster) and SAC-CI study on the valence and Rydberg excitations and ionizations of benzene including both and spaces. The importance of the reorganization effect is found for the T₃(³B_2u), S₂(¹B_1u), and S₃(¹E_1u) states, so-called V states. A first systematic calculation is reported for the Rydberg excited states. Next, the idea of the exponentially generated wave function (EGWF) theory is explained. New exponential-type operators and new wave functions associated with them are defined. The mixed or multi use of these exponential operators is shown to be effective both physically and practically. We call the resultant wave functions MEG (multi-exponentially generated) wave functions. We then explain the algorithm of calculations and show some results on the potential energy curves of the ground, excited, and quasi-degenerate states of some diatomics and triatomics.     

The relaxation spectra of nickel(II) and cobalt(II) arginine complexes

The temperature-jump method has been used to determine the nickel(II)- and cobalt(II)-arginine complexation kinetics. In the pH range studied, the neutral form of the ligand, HL, is the attacking, as well as the complexed, ligand species. The reactions reported on are of the type where n = 1, 2, 3 and M is Ni or Co. At 25° and ionic strength 0.1M the association rate constants are: for nickel(II) k₁ = 2.3 × 10³(±20%), k₂ = 2.4 × 10⁴(±20%), k₃ = 3.5 × 10⁴(±40%) M^?1 sec^?1; for cobalt(II) k₁ = 1.5 × 10⁵(±20%), k₂ = 8.7 × 10⁵(±20%), k₃ = 2.0 × 10⁵(±40%) M^?1 sec^?1. Arginine binds to metal ions less well than homologous chelating agents due to the electrostatic repulsion arising from the positively charged terminus of the zwitterion. Kinetically, the effect appears in the association rate constants with nickel reactions more strongly influenced than cobalt.     

Kinetics and mechanism of the thermal decomposition of cyclopentyl cyanide

The thermal decomposition of cyclopentyl cyanide has been investigated in the temperature range of 905–1143 K using both conventional stirred-flow reactor and very low-pressure pyrolysis (VLPP) techniques. The results from both techniques are consistent. The main primary processes are HCN elimination to form cyclopentene: and ring fragmentation to form vinyl cyanide plus propylene and ethylene plus cyanopropenes: Under the experimental conditions cyclopentene undergoes further decomposition to cyclopentadiene plus hydrogen. There is evidence for conversion of some of the reactant to a solid residue, presumably polymer. From the stirred-flow reactor results the following Arrhenius expressions were obtained: log k₁(s^?1) = (12.8 ± 0.3) ? (65.6 ± 1.3)/θ and log k₂(s^?1) = (16.0 ± 0.3) ? (80.0 ± 1.1)/θ, where θ = 2.303RT kcal/mol. Application of RRKM theory shows that the VLPP experimental rate constants are consistent with high-pressure Arrhenius parameters given by log k₁(s^?1) = (12.8 ± 0.3) ? (67.8 ± 2.5)/θ for HCN elimination, and log k₄(s^?1) = (16.3 ± 0.3) ? (80.1 ± 2.0)/θ for the sum of the ring fragmentation pathways. The rate parameters for HCN elimination are in good agreement with previous VLPP studies of alkyl cyanides and with theoretical predictions. The difference in activation energies for the ring opening of cyclopentane and cyclopentyl cyanide is reasonably close to the established value for the cyano stabilization energy. This supports the assumption of a biradical mechanism.     

Mechanism of catalytic ascorbic acid oxidation system Cu2+–ascorbic acid–O2

Analysis is made of reported results on the kinetics and mechanism of ascorbic acid oxidation with oxygen in the presence of cupric ions. The diversities due to methodological reasons are cleared up. A kinetic study of the mechanism of Cu²⁺ anaerobic reaction with ascorbic acid (DH₂) is carried out. The true kinetic regularities of catalytic ascorbic acid oxidation with oxygen are established at 2.7 ≤ pH < 4, 5 × 10^?4 ≤ [DH₂] ≤ 10^?2M, 10^?4 ≤ [Cu²⁺] ≤ 10^?3M, and 10^?4 ≤ [O₂] ≤ 10^?3M: where??₁ (25°C) = 0.13 ± 0.01 M^?0.5˙sec^?1. The activation energy for this reaction is E₁ = 22 ± 1 kcal/mol. It is found by means of adding Cu⁺ acceptors (acetonitrile and allyl alcohol) that the catalytic process is of a chain nature. The Cu⁺ ion generation at the interaction of the Cu²⁺ ion with ascorbic acid is the initiation step. The rate of the chain initiation at [Cu²⁺] ± 10^?4M, [DH₂] ± 10^?2M, 2.5 < pH < 4, is where??_i,1 (25°C) = (1.8 ± 0.3)M^?1˙sec^?1, E_i,1 = 31 ± 2 kcal/mol. The reaction of the Cu⁺ ion with O₂ is involved in a chain propagation, so that the rate of catalytic ascorbic acid oxidation for the system Cu²⁺? DH₂? O₂ is where??₁ (25°C) = (5 ± 0.5) × 10⁴ M^?1˙sec^?1. The Cu⁺ ion and a species interacting with ascorbate are involved to quadratic chain termination. By means of photochemical and flow electron spin resonance methods we obtained data characteristic of the reactivities of ascorbic acid radicals and ruled out their importance for the catalytic chain process. A new type of chain mechanism of catalytic ascorbic acid oxidation with oxygen is proposed: .     

Light-scattering characterization of poly(ethylene terephthalate)

By using a closed-circuit filtration system, we have succeeded in clarifying poly(ethylene terephthalate) (PET) dissolved in hexafluoroisopropanol (HFIP). Such static properties as the radius of gyration R_g, the weight-average molecular weight M_w, and the second virial coefficient A₂ and such dynamic properties as the translational diffusion coefficient D, or its equivalent hydrodynamic radius R_h, and the second (diffusion) virial coefficient k_d were determined for several PET samples of different molecular weights by using light-scattering intensity and linewidth measurements. An empirical relation between D_o (or R_h) and M_w was established: R_h = (1.77±0.15)X10^?2 M with R_h and M_w expressed in units of nanometers and grams per mole, respectively. The empirical exponent α_D(ca. 0.58±0.01) is in good agreement with the less precisely determined intrinsic viscosity/molecular weight exponent α_η (ca. 0.71±0.02). Several intensity correlation functions were measured very precisely using long accumulation times. A Laplace inversion was performed using the singular-value decomposition technique. The approximate molecular weight distribution (MWD) determined by light-scattering spectroscopy was in reasonable agreement with a completely independent determination of MWD using gel permeation chromatography (GPC). It was interesting to note, though not surprising, that GPC showed emphasis on lower-molecular-weight fractions, while light-scattering emphasized higher-molecular-weight fractions. The agreement further strengthens some complementary aspects of the two techniques.