Temperature effects on the relaxation parameters of the 1-methylnaphthalene excimer

The excimer lifetime τ_D and the excimer fluorescence efficiency for 1-methylnaphthalene in ethanol have been determined between −30 and 60°C. Expressing the rate constant for excimer deactivation. k_D, in terms of radiative k_FD) and nonradiative (k_ID) processes as k_D = k_FD + k_ID it is found that k_FD is independent of tempeature and k_ID = 5 × 10⁶ + 3.2 × 10¹¹ exp (-ΔE/RT) sec⁻¹, where ΔE = 6.7 kcal mole⁻¹. The behaviour of k_FD and k_ID with temperature and the appearance of isoemissive points in a limited region of temperature are discussed.     

Evaluation of kinetics parameters for poly(l-lactic acid) hydrolysis under high-pressure steam

In order to evaluate more precise kinetics parameters: rate constant k and E_a values for poly(l-lactic acid) hydrolysis, the reaction was carried out under high-pressure steam in a temperature range of 100-130 °C. Molecular weights of hydrolyzates were calculated by the universal calibration method without being influenced by any weight loss. The changes in molecular weight could be successfully explained according to the auto-catalytic hydrolysis mechanism, clearly indicating the critical point. Resulting k and E_a values were estimated as 8.4 × 10⁻⁵-7.2 × 10⁻⁴ s⁻¹ and 87.2 kJ mol⁻¹ with high R² values, respectively. Moreover, to determine the deviation of the parameter values, influences of four factors on the measurements and calculation: (1) use of number-average molecular weight value alone, (2) use of relative molecular weight based on polystyrene standards, (3) weight loss during the hydrolysis, and (4) selection of reaction mechanism were evaluated quantitatively.     

Etude de composés d'addition d'acides de Lewis,XXXIV [1] Composés d'addition de benzoquinone-1, 4 avec TiCl4

The adduct 1,4-benzoquine · TiCl₄ has been prepared in CH₂Cl₂ solution at about ?60°. Its IR. spectrum has been recorded at the same temperature. The experimental study of the vibrational frequencies has been completed by the calculation of the fundamental vibrations in the molecular plane, using Wilson's FG method, with slightly simplified models of 1,4-benzoquinone · TiCl₄ (13 masses) and 1,4-benzoquinone · 2 TiCl₄ (14 masses); analysis by use of internal and symmetry coordinates. An assignment of most of the observed bands is proposed and the conclusion is reached that the complex, when solid, is (1,4-benzoquinone · TiCl₄)_n. The force constants F(C? O) are 9,85 · 10⁵ dyne/cm for the quinone and 8,8 · 10⁵ dyne/cm for the disturbed carbonyl bond of the polymerized complex in the model proposed. At ordinary temperature in benzene solution of the components the adduct 1,4-benzoquinone. TiCl₄ · benzene precipitated; with the help of the models, the fundamental vibrations of its IR. spectrum have been assigned.     

Charge transfer properties of molecular complexes involving carbonyl bonds

The fraction of the dative structure, b² + abS, of hydrogen bonded complexes of N,N-dimethylacetamide with phenol derivatives and of charge transfer complexes of some aliphatic amides with iodine, is computed from the displacement of some vibrational modes. The values of b² + abS are computed from the v_co frequency shifts using a limiting value of 6 · 10⁵ dyne cm^?1 for the value of the force constant of the carbonyl bond in the dative structure.In the case of hydrogen bonded complexes, these results are compared with values of b² + abS computed from the Δv_OH stretching vibrations by the theory of Szczepaniak and Tramer. For the charge transfer complexes, the values of b² + abS are computed from the v_(I-I) stretching vibrations using the equation of Friedrich and Person. The agreement between the two methods is good in both cases.     

A time-resolved lif study of the kinetics of OH(ν = 0) and OH(ν = 1) with HCl and HBr

The kinetics of OH(ν = 0) and OH(ν = 1) have been followed using pulsed photolysis of H₂O or HNO₃ to generate hydroxyl radicals, and time-resolved, laser-induced fluorescence to observe the rates of their subsequent removal in the presence of HCl or HBr. The experiments yield the following rate constants (cm³ molecule^?1 s^?1) at 298 ± 4 K: OH(ν = 0) + HCl: k_o = (6.8 ± 0.25) × 10^?13; OH(ν = 0) + HBr: k_o = (11.2 ± 0.45) × 10^?12; OH(ν = 1) + HCl: k₁ = (9.7 ± 1.0) × 10^?13; OH(gn = 1) + HBr; k₁ = (8.1 ± 1.05) × 10^?12 For OH(ν = 1), the measurements do not distinguish between loss by reaction and relaxation, and the fact that k₁ > k_o for HCl is tentatively attributed to relaxation, probably by near-resonant vibrational—vibrational energy transfer. Clearly, neither of these exothermic, low-activation-energy reactions is enhanced to any great extent, if at all, by vibrational excitation of the OH radical.ft]*|Present address: Battelle/Pacific Northwest Laboratories, P.O. Box 999, Richland, Washington 99352, USA.     

Wetting properties of bis(trifluoromethyl)carbinyl acrylate polymers

A series of bis(trifluoromethyl)carbinyl acrylate monomers [Y-C(CF₃)₂ O? CO? CH?CH₂] in which Y is CH₃, CH₃CH₂, CH₃CH₂CH₂, CH₃CH₂CH₂CH₂, C₆H₅, H, F, CF₃, N₃, CN, and CH₃OCH₂CH₂O, was prepared. Polymers were easily prepared from all of these monomers except where Y = CN, wherein a variety of initiation methods failed to produce high molecular polymer. Wettabilities of the polymer films were examined by means of contact angle measurements by using n-alkane test liquids and water. Values of the dispersion force contribution (γs^d) and the polar force contribution (γs^p) to the solid surface energy were calculated by employing both geometric and harmonic mean approximations. Values of γs^d calculated by either method agreed well with γ_c (critical surface tension) values determined graphically from contact angle data employing n-alkane test liquids, confirming the suggestion that γ_c is an approximate measure of the dispersion force contribution to solid surface energy. Values of γs_d ranged from 15 dyne/cm (Y = F or CF₃) to 25 dyne/cm (Y = C₆H₅). Values of the polar force contribution to solid surface energy (γs^p) varied from 0.6 dyne/cm (Y = CH₃CH₂CH₂CH₂) to 3.4 dyne/cm (Y = CH₃OCH₂CH₂O) when calculated by the geometric mean equation. The values of γs^p obtained from the harmonic mean equation followed the same trend upon varying substituents, but were larger in value, ranging from 2.9 dyne/cm (Y = CH₃CH₂CH₂CH₂) to 7.5 dyne/cm (Y γ CH₃OCH₂CH₂O).     

Studies on the structure of the urea-orthoboric acid complex

Thermal and infrared spectral studies of the urea-orthoboric acid complex are reported. The complex is formed through the elimination of 0.5 H₂O molecule. Infrared spectral data show the presence of hydrogen-bonding and the force constant calculated for the N ... HO bond is found to be 4–5×10^–5 dyne cm^–1, which is for the order of a single bond and indicates strong hydrogen-bonding in the complex. A tentative structure for the complex is proposed.     

Vibrational rate enhancement in the reaction OH + H2(ν = 1) → H2O + H

The rate constant for the reaction between OH and vibrationally excited H₂, OH + H₂(ν = 1)→H₂O + H, has been measured directly at 298 K. k₀₁ is found to be (7.5±3)×10^?13 cm³/molecules, corresponding to a vibrational rate enhancement of k₀₁/k₀₀ = (1.2 ± 0.4) × 10².     

Electrode kinetic studies of single electron charge transfer redox couples using the faradaic rectification method

Three single electron charge transfer redox reactions have been studied using the faradaic rectification method. The kinetic parameters obtained for the ferricyanide-ferrocyanide redox couple are α=0.49, k_a⁰=12×10^?2 cm s^?1; for the chromic-chromous system α=0.47, k_a⁰=2×10^?3 cm s^?1 and for the titanic-titanous reaction α=0.49 and k_a^o=6×10^?4 cm s^?1 at 27°C.     

Rate constant for the reaction of nh2 with ozone in relation to atmospheric processes

The absolute rate constant of the reaction between NH₂ and ozone has been measured using a flash photolysis-laser resonance technique and found to be k₄ = 6.3 (=1.0) × 10^?14 cm³ molecule^? s^?1 at room temperature. The Arrhenius expression, determined from measurements in the temperature range 298–380 K is k₄ = 4.2 × 10^?12 exp(?2.5 = 0.5/RT) (E in kcal mole ^?1. The possibility of formation or elimination of nitrogen oxides from the reactions of NH₂ in the atmosphere is examined.     

Reversible intersystem crossing,fluorescence lifetime lengthening and collisionally induced phosphorescence in biacetyl

The emissions of biacetyl excited at 4200 Å were studied at pressures down to 10^?3 torr. Apart from the well-known nanosecond fluorescence, a new emission of the same spectral composition was found with a non-exponential decay in the microsecond range. Furthermore the phosphorescence, as defined by its spectral composition, was found to be collisionally induced.The results imply that after excitation, the molecule rapidly transfers (rate constant k_S→T) to the triplet state, giving rise to the nanosecond decay time; and can then transfer back to the singlet state (rate constant k_T→S), giving rise to the microsecond emission. At the same time internal conversion can occur (k_S→S0). From an analysis of the data we find for k_S→S0 = 2.4 × 10⁷ sec^?1, k_S→T = 7.6 × 10⁷ sec^?1, k_T→S = 1.9 × 10⁵ sec^?1. The kinetic treatment can be transformed to a quantum mechanical one, yielding values for the triplet level density (?_T), the coupling element V_ST and the number of triplet states (N) coupled to the singlet excited. At 4200 Å we find ?_T = 6.3 × 10⁵cm, V_ST = 1.0 × 10^?5 cm^?1, N = 400.Phosphorescence occurs only when the molecule is deactivated by collisions to a vibronic triplet state below the vibrationless excited singlet state. The efficiency of biacetyl collisions is 0.54.     

Antioxidant Activity of Adamantylphenols

Antioxidant properties of phenols with ortho- and para-adamantyl substituents are studied by microcalorimetry using cumene oxidation as a model reaction. The experimental rate constants for inhibition by adamantylphenols (k ₇) are comparable to the corresponding values for sterically hindered phenols, and the stoichiometric inhibition coefficient is higher than the calculated one. Adamantylphenols with adamantyl and methyl or methylene bridge groups in the ortho positions with respect to the functional group exhibit the maximal activity. The inhibition rate constant takes a maximal value of k ₇ = 3.3 × 10⁴ l mol^–1 s^–1 for 2,4-di-(adamantyl-1)-6-methylphenol and a minimal value of k ₇ = 1.4 × 10³ l mol^–1 s^–1 for 2,4,6-triadamantylphenol. The difference in the rate constants is due to steric hindrances in the reaction of a peroxy radical with the functional group of a phenol surrounded by bulky adamantyl groups.     

Fermi resonance perturbations between (νβ=n) and (νσ=1, νβ=n−2) states in the rotational spectrum of HCN…HF

A useful graphical method for the assignment and analysis of the effects of Fermi resonance in rotational spectra has been devised and applied to vibrational satellites in the microwave spectrum of H¹²C¹⁴N…H¹⁹F. The analysis leads to a value of 7.4 cm⁻¹ for the cubic potential constant k_σββ.     

Simultaneous vibrational and rotational transitions in hydrogen + argon at high collision velocities: Collisions at nonzero impact parameters

The problem of vibrationally and rotationally inelastic scattering processes in H₂ + Ar for nonzero impact parameter b has been investigated in the collision velocity range of 10⁶–10⁷ cm/sec by use of the sudden approximation. The simultaneous vibrational (0 → 1) and rotational (00 → 00, 20, or 40) transitions were studied. For υ > 3 x 10⁶ cm/sec, the probabilities for b/l = 1.0 are found to be very large compared with those for b = 0, where l is the hard-sphere collision diameter; for b/l > 1.0, the probabilities decrease very rapidly with increasing b. The results show that nonzero-b collisions must be included in the calculation of simultaneous transition processes in H₂ + Ar at higher collision velocities.     

Vibrational relaxation of HF(υ = 3,4)

The vibrational relaxation of pure HF(υ = 3 and υ = 4) has been studied by pumping HF directly from υ = 0 to υ = 4. The relaxation rates of υ = 3 and υ = 4 were determined to be k³_T = (2.8 ± 0.4) × 10^?11 cm³ molecule^?1 s^?1 and k⁴_T = (7.2. ± 0.5) × 10^?11 cm³ molecule^?1 s^?1 at 293 K. It is shown that sigle quantum energy transfer can account for all the vibrational relaxation.     

Rate Constant for the Reaction of the OH-Radical with CH2F2

The rate constant value of k ₁ = (6.05 ± 0.20)×10⁹ cm³ mol^–1 s^–1 (with ± 1 error) has been determined for the reaction OH + CH₂F₂ (1) by applying the discharge-flow/resonance-fluorescence method at 298 K.     

Cinetique complexe de l'halogenation de cetones en milieu acide—I : Iodation des enols

The kinetics of the iodination of acetone, diethylketone and di-isopropylketone in aqueous media ([H₂SO₄] = 0·1 to 1·0 N; [I₂]_a^o = 10^?7 to 10^?5M) have been studied by couloamperometry under irreversible conditions. At these concentrations the rates of formation of the enol and of its iodination are similar. The general equation, which assumes the steady state approximation for the enol, is applicable, and is used to separate the rate constants of enolisation (k₁) and the apparent enol iodination rate constant (k_II^I₂ = K_Ek₂^I₂). For acetone, the value given by Schwarzenbach for the enol equilibrium constant (K_E = 2·5 x 10^?6) leads to an elementary rate constant for the addition of iodine to the enol (k₂^I₂ = 6·5 x 10⁶ M^?1s^?1). This value is not, however, consistent with k_I2 = 1·5 x 10⁸ M^?1s^?1, the rate constant for the iodination of the corresponding ether 2-ethoxypropene.     

Elastic constant anisotropy,core structure of wedge disclinations and optical texture of main-chain P-4-BCMU liquid crystals

The elastic constant anisotropy and the core structure of wedge disclinations with strengths s = ±½ of lyotropic liquid crystals of a soluble polydiacetylene, P-4-BCMU (M _w = 5.15 × 10⁵, M _n = 2.16 × 10⁵, and M _w/M _n = 2.4), in chloroform was studied. The Frank elastic constant anisotropy defined by ε = (k₁₁ ? k₃₃)/(k₁₁ + k₃₃) for this polymer was determined by three different methods. The results show that the value of ε for this polymer is 0.5 (±0.05) in solid state and/or in liquid crystal state, indicating that the splay constant k₁₁ is three time higher than the bend constant k₃₃. This result further implies that splay is unfavorable in the liquid as it requires greater energy than bend. In the area adjacent to the core of a singularity the value of ε increases with decreasing distance to the core, indicating increasing anisotropy of the elastic constants toward the core. The influence of the elastic constant anisotropy on the optical texture of the LC polymer when viewed by polarizing light microscope is studied. © 1994 John Wiley & Sons, Inc.     

Reactions of the HO2 radical with OH,H, Fe2+ and Cu2+ at elevated temperatures

The temperature dependence of the rate constant for the reactions of HO₂ with OH, H, Fe²⁺ and Cu²⁺ has been determined using pulse radiolysis technique. The following rate constants, k (dm³ mol⁻¹ s⁻¹) at 20°C and activation energies, E_a (kJ mol⁻¹) have been found. The reaction with OH was studied in the temperature range 20–296°C (k=7.0×10⁹, E_a=7.4) and the reaction with H in the temperature range 5–149°C (k=8.5×10⁹, E_a=17.5). The reaction with Fe²⁺ was studied in the temperature range 16–118°C (k=7.9×10⁵, E_a=36.8) and the reaction with Cu²⁺ in the temperature range 17–211°C (k=1.1×10⁸, E_a=14.9).     

Ac polarography and faradaic impedance of strongly adsorbed electroactive species: Part IV. Experimental study of the faradaic impedance of the redox systems benzo(c)cinnoline-dihydrobenzo(c) cinnoline

The faradaic impedance of the surface redox system benzo(c)cinnoline-dihydrobenzo(c)-cinnoline is studied experimentally in aqueous medium between pH 5 and 13. The variations of the impedance components are in good accord with the theoretical predictions. A V-shaped curve is found for log k_s=f(pH) (k_s=rate constant of the surface electrochemical reaction). It is estimated that the determination of rate constant values up to 2×10⁴ s^?1 on a mercury electrode is possible by this method.