J. C. Leyte

Intermolecular vibrational relaxation in liquids

Abstract The influence of intermolecular vibrational relaxation on dipole moment correlation functions, as obtained from IR band shapes, is discussed. It is explicitly shown that vibrational relaxation due to intermolecular interactions depends on the reorientational behaviour of the molecules in the liquid. Therefore, an a priori separation of the dipole moment correlation function into independent reorientational and vibrational factors is not generally possible. The implications for various procedures used to “correct” Raman and IR band shapes for vibrational relaxation are discussed. The expression derived for the intermolecular vibrational relaxation is used to calculate theoretically the effect of transition dipole-transition dipole coupling on dipole moment correlation functions. Experimental data obtained from isotopic dilution measurements support the interpretation of the isotopic dilution effect in terms of the transition dipole-transition dipole coupling.

On the single-molecule dynamics of water from proton, deuterium and oxygen-17 nuclear magnetic relaxation

Abstract Comparison of the nuclear relaxation rates of H, D and 17 O shows the isotropic motional model to be adequate for H 2 O on the picosecond timescale.

Long-range electric field gradients in charged polymer solutions as probed by 23Na relaxation

Bi-exponential 23Na nuclear magnetic relaxation is shown to be a general phenomenon in aqueous solutions of charged polymers in the semi-dilute region. Dependence on concentration, degree of polymerization, degree of ionization and presence of simple salt is established and discussed.

Physico-chemical properties of aqueous solutions of xanthan: an n.m.r. study.

The conformations of xanthan in aqueous solution as a function of temperature have been studied. Measurements of optical activity indicate that the conformational transition, induced by varying the polymer concentration, is analogous to that induced by changes in ionic strength and pH. Within a certain range of concentrations, the low-temperature conformation has a molecular-weight-dependent stability, which shows the usual sigmoidal melting profile with increase in temperature. The 13C-n.m.r. data reflect the increase of the mobility of C-1 and the side-chain carbon atoms in the transition-temperature region. The 23Na relaxation behaviour changes on melting the ordered xanthan conformation. At least two correlation times are needed in order to describe the field-strength dependence of the longitudinal and transverse 23Na relaxation. At 25 degrees, a value of 6.8 ns is obtained for the largest correlation time for the fluctuation of the electric-field gradient. The high-temperature conformation also generates correlation times of the order of ns. From 17O relaxation measurements, a reduction of the mobility of water molecules in the presence of xanthan chains is also observed.

Nuclear relaxation and counterion behaviour in solutions of charged macromolecules. Correlation times from relaxation of I = 32 nuclei

Abstract From the relaxation of 23 Na in poly(methacrylic acid) solution at field strengths corresponding to 23 Na frequencies from 8 to 64 MHz, spectral densities in the range 0–128 MHz were derived. The results are used to discuss the uncertainties connected with current methods to determine correlation times from the nuclear relaxation of small ions in macromolecular solutions.

On the concentration dependence of the nature of polyelectrolyte solutions as detected by 23Na relaxation

Abstract Dependence of 23 Na nuclear magnetic relaxation on concentration and degree of polymerization is reported for solutions of Na polystyrenesulfonate. In the concentration range 10 −1 ⪯ c 10 −1 eq/e, 23 Na relaxation is far outside the extreme-narrowing limit and relaxation rates depend on the degree of polymerization. These phenomena seem to disappear outside this range.

Solvent dynamics in aqueous PEO–salt solutions studied by nuclear magnetic relaxation

The dynamical behaviour of water in aqueous PEO solutions has been studied by 2H and 17O nuclear magnetic relaxation measurements. A two-phase model is introduced to analyse the water mobility in the PEO hydration phase. The water mobility in the hydrated phase is retarded by a factor of 2 to 5. The anisotropic reorientation of water molecules in the proximity of PEO and the dP-dependence on the 2H and 17O relaxation rates are interpreted qualitatively by local PEO dynamics, preferential orientations of water molecules and deuteron exchange among water molecules and hydroxy end-groups.

Isotopic dilution effect on the IR absorption bandshape of CH2Cl2

Abstract The shape of the 1265 cm −1 absorption band in liquid CH 2 Cl 2 changes on dilution with the deuterated compound. This is discussed in terms of intermolecular vibrational relaxation. The important influence of molecular reorientation on vibrational relaxation is pointed out.

The intramolecular OH bond length of water in a concentrated poly(ethyleneoxide) solution. An NMR relaxation study

Abstract The proton relaxation rates of normal well as 17O-enriched water and the deuterium relaxation rate in 2H-enriched water were measured in 10 monomolal poly(ethyleneoxide) solutions. The 17O1H intramolecular dipolar contribution to the proton relaxation rate was determined. From these experimental parameters the intramolecular OH-bond distance in the water molecule was calculated. It was found that this distance is increased by a small (1%) but significant amount compared to the pure water value. The results indicate that the solvent shows increased hydrogen bonding at the hydrophilic as well as the hydrophobic interface.

On the structure and dynamics of water in AlCl3 solutions from H, D, 17O, and 27Al nuclear magnetic relaxation

The relaxation rates of 27Al, H, D, 17O, and the relaxation rate of H due to dipolar coupling to 17O were obtained in a series of aqueous AlCl3 solutions. From these data conclusions are reached about bulk water dynamics, the O–H bond distance, and the order within the Al3+ hydration shell. The bulk water dynamics is interpreted by a hydrodynamical model. For comparison viscosity data are presented. It is found that the change in the O–H distance of water molecules adjacent to Al3+ is significant and in agreement with reported theoretical results. The destruction of order within the Al3+ hexaquo complex with increasing concentration is indicated.