The spin-lattice relaxation time T₁ has been measured for the proton and the deuteron resonances in methane -and its deuterated modifications as a function of density ƿ , at low densities where T₁ is proportional to ƿ ; and temperature T, between 110°K and 300°K. For the proton relaxation, plots of log T₁/ƿ versus log T for each of the gases CH₄₌ո Dո, n=0, 1, 2, 3 gave the temperature dependence of T₁/ƿ as T₁/ƿ∝T⁻³ʹ² . The value of T₁/ƿ at constant temperature changed very little with n. This implied that the main interaction contributing to proton spin relaxation was the spin-rotational interaction. For the deuteron results it was found that T₁/ƿ was nearly independent of temperature but differed by a factor of approximately four over the range of isotopic compositions n = 1, 2, 3,4. CD₄ gave the shortest value of T₁ while CHD₃ gave the longest. This was attributed to the dominance of the quadrupolar interaction of the deuteron over the dipolar and spin-rotational interactions. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Bibliography: p. 212-221. / Coincident protons from the reaction ¹²C(p,2p) at an incident proton energy of 200 Me V, have been measured using conventional particle telescopes. Data were acquired at nine pairs of angles (θ₂=20°, 45°, 70°, 95°, 120° and 145° for θ₁ =-20°, and θ₂=35°, 85° and 135° for θ₁ =-45°). An improved model, based on previous theoretical and experimental work, has been proposed to describe the reaction mechanism leading to the observed coincident proton yield from the nuclear continuum. This model considers an initial quasifree nucleon-nucleon interaction - described by a distorted wave impulse approximation (DWIA) treatment - between the incident proton and a single target nucleon, followed by the rescattering of the struck nucleon, which behaves as an intranuclear projectile, from the spectator part of the target nucleus. The validity of the DWIA treatment used in the continuum study, has been tested by analysing the kinematic regions of the coincident proton energy spectra corresponding to the knockout of protons from the outer lp3/2 orbital of ¹²C which do not undergo further interactions with the residual nucleus. Good agreement in shape has been found between the calculated and measured cross sections in the kinematic region of interest to the continuum study. An average spectroscopic factor of 1.1±0.3 was extracted. Except in the -20°,20° case, the DWIA treatment was found to be insensitive to the choice of the initial or final energy prescriptions for the two-body scattering approximation. Nonlocality effects were found to be small, changing the absolute value of spectroscopic factors by a maximum of 20%. Coincident continuum cross sections were extracted from the experimental data corresponding to the detection of protons at the θ₁ angles with energies of 70±5 MeV, 100±5 MeV and 130±5 MeV. Comparisons were made with calculations which modelled the proposed reaction mechanism in terms of a convolution integral over the DWIA cross sections describing the initial quasifree knockout process and experimental inelastic scattering probabilities describing the further multiple scattering interactions undergone by the knocked out nucleons. Good agreement has been found between the normalized calculated and measured continuum cross sections (spectroscopic factors varying from 0.8 to 2.3 between sets of data, depending on the kinematic region sampled and the prescription used for the two-body scattering approximation). It has been shown that contributions from nucleons that are knocked out both in- and out-of-plane in the initial quasifree process should be considered, and that the contribution from neutron knockout in the initial interaction is significant, ranging from 0.13 to 0.62 that of the proton knockout contribution.

Calorimetric ΔH° values are given for stepwise proton dissociation from the protonated o-, m-, and p-aminobenzoic acids together with ΔH° values for proton ionization from the three corresponding methylaminobenzoates. The pK_1 values for the m- and p-aminobenzoic acids and pK values for the methylaminobenzoates were determined both by the entropy titration procedure and by the pH titration method. The pK_1 value for o-aminobenzoic acid was determined by entropy titration and the pK_2 values for o- and m-aminobenzoic acids were calculated from pH titration data. The ratios (K_Z) of the molar concentrations of zwitterion and neutral molecule for the three aminobenzoic acids were determined by both a pK method and a calorimetric method. An error analysis is made to provide insight into the relative merits of the two methods, and criteria are given which provide the best method for K_Z determination for any specific case. Microconstant, microenthalpy change, and microentropy change values are calculated for proton ionization from protonated m- and p-aminobenzoic acids from their respective K_Z and macrothermodynamic values. Previously, the calculation from calorimetric titration data of free energy, enthalpy, and entropy change values for protonation reactions in aqueous solution using stong acid or base solution as the titrant has been limited to substances whose pK values are either less than four or greater than ten. In this study, it is shown that the entropy titration method can be extended using weak acid or base solutions as titrants to cover the intermediate pK range ( 4>pK>10). To illustrate the applicability of this method using a weak acid titrant, pK, ΔH°, and ΔS° values for proton ionization from metanilic acid, pyridinium ion, imidazolium ion, protonated tris(hydroxymethyl)aminomethane and glycine have been determined from calorimetric titration data using a solution of acetic acid as titrant. Criteria are presented for titrant selection so the pK, ΔH°, and ΔS° values for any substance may be precisely and accurately determined by this method. A calorimetric study has been made of proton ionization from 71 protonated amines in aqueous solution at 25°. The resulting ΔH° values were combined with pK values to calculate ΔS° values. pK values were taken from the literature for 53 substances and new values were determined for 18 substances. A compilation of pK, ΔH° and ΔS° values from the present study and the literature is given for proton ionization from 171 amines. Hydrocarbon chain lengthening and branching effects on ΔH° and ΔS° values for proton ionization from primary and secondary aliphatic amines can be described by simple linear equations. Proton ionization from amines was not found to follow the linear relation between ΔG° and ΔS° predicted by the Bjerrum theory of electrostatics. The changes in ΔH° and ΔS° from the first to the second step of ionization for 37 diamines have been examined using the Bjerrum and Kirkwood-Westheimer theories of electrostatic interactions in aqueous solution. A deviation for the diamines, identical to that previously found for dicarboxylic acids, was found between the results derived from the experimental data and those predicted by the Kirkwood-Westhiemer theory. Possible reasons for this deviation are discussed.

A calorimetric study has been made of proton ionization in dilute aqueous solution from aliphatic carboxylic acids at 10, 25, and 40° (13 acids) and at 25° (3 acids). Values of ΔS° are calculated by combining the resulting ΔH° values with ΔG° values obtained from the literature or determined from potentiometric or calorimetric measurements. The trends in ΔG°, ΔH°, and ΔS° are described by an electrostatic model, and deviations from this model are taken as a measure of nonelectrostatic substituent effects for carboxylic acids. A calorimetric study has also been made of proton ionization in dilute aqueous solution from several primary, secondary and tertiary amines at 10, 25 and 40°. ΔCp° values have been calculated and correlations made between ΔCp° values for proton ionization of several acids and amines and the dipole moments of the unprotonated acids or bases. Linear enthalpy-entropy relationships have been observed for proton ionization as a function of temperature. An equation has been derived to use this linear relationship between ΔH° and ΔS° to calculate ΔG° values at temperatures where only ΔH° values are available.

Bibliography: pages 56-57. / Angular distributions have been measured for the radiative proton capture reaction ¹²C(p,ϒ)¹³N at beam energies from 40 to 54 MeV. Measurements were made with the new, large anticoincidence-shielded spectrometer HA GAR at angles from 30° to 150° to the beam direction. Differential and total cross-sections have been calculated from these data, and show evidence for resonant behaviour for the transitions to the ground state, the first excited state, and the unresolved second and third excited states. The total cross-sections for these transitions peak at a proton energy of about 46 MeV which is twice the centroid energy of the Giant Dipole Resonance (GDR) based on the ground state of ¹³N.

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