Showing papers by "J. Mayers published in 2002"

Direct observation of tunneling in KDP using Neutron Compton scattering.

Abstract: Neutron Compton scattering measurements presented here of the momentum distribution of hydrogen in KH 2 PO 4 just above and well below the ferroelectric transition temperature are sufficiently sensitive to show clearly that the proton is coherent over both sites in the high temperature phase, a result that invalidates the commonly accepted order-disorder picture of the transition. The Born-Oppenheimer potential for the hydrogen, extracted directly from data for the first time, is consistent with neutron diffraction data, and the vibrational spectrum is in substantial agreement with infrared absorption measurements. The measurements are sensitive enough to detect the effect of surrounding ligands on the hydrogen bond, and can be used to study the systematic effect of the variation of these ligands in other hydrogen bonded systems.

Momentum-distribution spectroscopy using deep inelastic neutron scattering

Abstract: We show that deep inelastic neutron scattering from hydrogen (or other light nuclei) can be used to measure a spectrum of anharmonic contributions to the target atom momentum distribution with high and known accuracy. The method is applied here to determine the momentum distribution of the hydrogen in the hydrogen bonded system ${\mathrm{KHC}}_{2}{\mathrm{O}}_{4}$ (potassium binoxalate), where 23 anharmonic coefficients are obtained at better than the $2\ensuremath{\sigma}$ level. The momentum distribution is obtained to an accuracy of better than few percent at all significant values of momentum.

Sub-femtosecond dynamics and dissociation of C-H bonds in solid polystyrene and liquid benzene

Abstract: In previous work [C. A. Chatzidimitriou-Dreismann et al., J. Chem. Phys. 113, 2784 (2000)] we provided first results of the subfemtosecond dynamics of C–H bond dissociation of solid fully protonated polystyrene at T≈295 K, applying neutron Compton scattering (NCS). A striking anomalous shortfall of the proton scattering intensity with respect to that of the carbon nucleus has been observed. A theoretical explanation based on short-lived protonic quantum entanglement (QE) has also been given. Here we present a twofold extension of that work: Investigation of the found anomaly (i) in solid D-polystyrene with various degrees of aromatic protonation [(-CD2CDC6HxDy-)n with x+y=5] and (ii) in liquid C6H6 and C6H6–C6D6 mixtures. A striking decrease of the neutron cross-section density of H by 20% (on the average) was observed, which appeared to be weakly dependent on the H:D atomic ratio. This result indicates that the considered effect is mainly of intramolecular origin. In contrast to previous NCS experiments ...

Experimental test of a theoretical analysis of deep inelastic neutron scattering experiments for H and D nuclei

Abstract: In a recent paper by Blostein et al. (Physica B 304 (2001) 357) was presented a critical theoretical analysis of different procedures, with which data of deep inelastic neutron scattering (DINS) experiments are usually processed. One part of that criticism—which is experimentally tested in the present paper—claimed the existence of serious errors in the determined areas of overlapping DINS-peaks, in particular in the case of the considerable overlapping of the strong proton peak with the weak deuteron peak. Our experimental test presented here consists in the comparison of the D-peak areas determined from DINS-data of H/D mixed systems, taken in both the “forward” and the “backward” scattering directions. Since there is no H-peak in the “backward” scattering direction, the claimed error cannot occur in this regime. New experimental results from (A) pure D2O, and (B) the equimolar H2O/D2O mixture, are presented. The liquids were contained in a Nb can. For both systems, it is shown that the D-peak areas in the “forward” and the “backward” scattering directions are essentially equal. This proves that the aforementioned criticism, although very stimulating, is of no relevance in the specific context of our (previous and present) DINS experiments. Moreover, the new experiments show that the cross-section of D is fully consistent with conventional expectations.