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Deals with a study which examined a combination of Monte Carlo and Simplex iterations for the measurement of nuclear magnetic resonance relaxation in developing porous structures. Information on the numerical method; Application in simulated data; Application in the study of cement hydration.

The vibronic spectrum of the allyl radical (CH[sub 2]CHCH[sub 2]) at 6-8 eV has been observed using 2+1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The allyl radicals were produced in the nozzle of a supersonic jet expansion by the pyrolysis of allyl iodide. Five new Rydberg states, a 3d and four ns states (n=4,6-8), are observed for the first time. Prominent vibrational progressions with the gross spacing of ∼430 cm-1 are observed in the s Rydberg series. The totally symmetric /_ CCC-bending vibration in the Rydberg states is responsible for the observed vibrational progressions. Facilitated with the ab initio calculation of Franck-Condon factors, other observed vibrational states in the s Rydberg series have been identified. The term values for the ns Rydberg series converge to an adiabatic ionization energy of 65 638±18 cm[sup -1] with a quantum defect of 0.966±0.005. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

When placed into an external magnetic field inhomogeneous porous structures, like rocks, cement gels, ceramics, etc., exhibit strong local magnetic field gradients (LMFG), which are inherently related with the size, shape, and distribution of their pores. In this paper, we present a method of measuring LMFG in a liquid-filled porous media, provided that the fast exchange model sufficiently describes water motion in the pores, which is based solely on the measurement of the water [sup 1]H NMR spin lattice relaxation rates and the knowledge of the unrestricted diffusion coefficient. The method is applied to two hydrating white cement samples with different hydration kinetics, and the results are correlated with the time evolution of the pore structure. It is shown that the measured LMFG have extremely high values, which qualitatively reflect the sharp needlelike morphology of the internal cement gel surface. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]