Kinetics of the Fe3+ ion–H2O2 reaction: Steady-state and terminal-state analysis

Computer calculations of the kinetics of the ferric ion catalyzed decomposition of H₂O₂ by Walling and Weil are not in contradiction to the “complex mechanism.” The examination of their results reveals that their simulations correspond to the terminal state of the system in which the secondary complex between Fe³⁺ and H₂O₂ becomes stabilized.     

On the density expansion of spectral lineshapes

We compare two types of expansions (in the density of perturbers) of collisionally broadened spectral lineshapes. The first is the more conventional frequency-domain expansion of Fano whereas the second is made in the time domain. In the impact limit they both predict a simple lorentzian line shape but otherwise they yield very different results upon trunction. Our calculations indicate that the time-domain expansion is more adequate and should be preferred.     

Rigid backbone polymers. X. Transitions in bulk polyisocyanates

Data obtained by hot-stage cross-polarized light microscopy and thermogravimetric analysis were used to plot a transition map for the poly(n-alkylisocyanate) homologous family. Most members had a low-temperature transition (or relaxation). The middle members of the family, with side-chain length of 4 ≤ n < 13 carbon atoms, exhibit a mesomorphic range of temperatures. Members with sidechains of n ≥ 13 in length, go directly from the low-temperature transition to the melting point without passage through a liquid crystalline state. A transition map for two homopolymers and a series of their copolymers, poly[x mol% n-butyl + (100-x)mol% p-anisole-3-propyl]isocyanate, was also prepared. The range of mesomorphicity as a function of composition and temperature is clearly indicated.     

Bayesian inference for the power law process

The power law process has been used to model reliability growth, software reliability and the failure times of repairable systems. This article reviews and further develops Bayesian inference for such a process. The Bayesian approach provides a unified methodology for dealing with both time and failure truncated data. As well as looking at the posterior densities of the parameters of the power law process, inference for the expected number of failures and the probability of no failures in some given time interval is discussed. Aspects of the prediction problem are examined. The results are illustrated with two data examples.     

Diamagnetic susceptibility effects in NMR measurements of the properties of water in polymeric membranes

The NMR spectra of water adsorbed at various relative humidities on various cellulose ester membranes have been studied. Membranes of cellulose acetate (CA), cellulose triacetate (CTA), and cellulose acetate butyrate (CAB) were investigated. It was found that the resonance peak of a liquid imbibed in or adsorbed on membranes from high relative humidity is very sensitive to the angle between the membrane plane and the direction of the magnetic field, shifting 5–7 ppm to higher fields as the membrane plane is rotated from a perpendicular to a parallel position with respect to the direction of the external magnetic field. This phenomenon was found to be independent of the nature of the polymeric material (namely CA, CTA, or CAB), porosity of the membrane (varying from an “all bulk” dense sheet to an 80% porosity and 0.2 μm average pore size membrane), nature of the magnetic nuclei (H₂O or D₂O), intensity of the external magnetic field (60 Mcps or 100 Mcps), and nature of the liquid in the membrane (water, methanol, or n-hexane). It is therefore concluded that the dependence of the position of the resonance peak on the position of the membrane plane with respect to the external magnetic field, is a geometrical phenomenon due to the magnetic “bulk susceptibility” of the medium. Quantitative estimations of the magnitude of the diamagnetic susceptibility effect in a cylindrically rolled sheet are given. These estimates agree well with the experimentally observed “splittings.”     

The energy dependence of 18O(π+, π−)18Ne(gs)

Eight angular distributions measured for ¹⁸(π⁺, π^?)¹⁸Ne(gs) across the Δ₃₃ resonance show the details of the energy dependence of the reaction. At higher energies, the maximum is at q ? 0.85 fm^?1, in agreement with simple sequential scattering models, but a lower energies it is at q ? 0.5 fm^?1, with the transition occuring over a narrow energy range.     

Spectral lineshapes of molecular clusters

The electronic spectral lineshape of an impurity molecule in a cluster is calculated. Both a rigid (solid-like) and a non-rigid (droplet-like) model for the cluster are considered and compared. The spectrum is calculated using the spectral density J(ω) which is related to the correlation function of the time-dependent enegy gap between the two electronic states. Our calculations demonstrate how the information regarding individual eigenstates is lost under the broadened lineshape envelope in large clusters.     

Structure of 14C from 12C(t,p)

The reaction ¹²C(t, p)¹⁴C has been investigated with an 18 MeV triton beam. Twenty energy levels of ¹⁴C were identified up to 13 MeV excitation. Angular distributions were measured and compared with DWBA calculations. A previously unreported 0⁺ level at 9.75 MeV was observed; it undoubtedly corresponds to the second predominantly sd shell 0⁺ state in ¹⁴C. Additional spin and parity assignments have been made in the present work: 9.81 MeV, (1^?); 10.43 MeV, 2⁺; 10.50 MeV, (3^?); 10.74 MeV, 4⁺; 11.40 MeV, 1^?; 11.67 MeV, (1^?); 11.73 MeV, (5^?); 12.58 MeV, (2⁺, 3^?); 12.87 MeV. 2⁺, 3^?; and 12.96 MeV, (1^?); none of which had a definite spin and parity assignment previously. Our results confirm the previous information on the level structure of ¹⁴C below 8.5 MeV. The cross section for the unnatural parity state at 7.34 MeV, J^π = 2^?, is well reproduced by a two-step reaction calculation. The results are compared with the predictions of a weak coupling model.     

Photochemical studies—XXI : Dimers of 3,4-(o,o'-biphenylene)cyclopentadienones: Thermal and photochemical behaviour

The 1,4-dimethyl-, 1,2,4-trimethyl and 1,2,4,7-tetramethyl substituted 3,4-(o,o'-biphenylene) cyclopentadienone-dimers (6a–6c) were prepared and found to undergo photochemically or thermally a 1,3-rearrangement to the centrosymmetrical diketones (11). Only the tetramethyl derivative (6a) undergoes at room temperature a fast, degenerate [3.3] Cope rearrangement with ΔG^≠₂₃₃ = 11.4 kcal mol.^?1 All these dimers and rearrangement products appear not to dissociate to their monomers, but react with dienophiles to give the adducts (12, 13). A stepwise mechanism involving diradical intermediates (19) is invoked. The “mixed dimer” (14) was also prepared and studied. The steric and electronic effects determining the behaviour of these compounds are discussed.