Characterization inelastic neutron scattering

Role of adsorbed hydrogen species on ruthenium and molybdenum sulfides. Characterization by inelastic neutron scattering, thermoanalysis methods and model reactions. 

Highly energetic compounds with potential use in explosive devices must be characterized completely and safely, particularly as the explosive character may be linked directly to vibrational modes in the molecular structure, hence the application of computational methods to complement experimental observations. ANTA 5 has been the subject of various studies and, as an adjunct to one of these and to confirm the results of an inelastic neutron scattering experiment, an isolated molecule calculation was carried out using the 6-311G basis set <2005CPL(403)329>. 

In this paper we discuss how neutron scattering spectroscopy can be applied to the study of the structure and dynamics of adsorbed molecules. Since reviews of elastic and inelastic neutron scattering from adsorbed films have recently appeared (1.-3), our purpose here is not to present a comprehensive survey of every adsorbed system investigated by neutron scattering. Rather, we shall be concerned primarily with two questions which are basic to the characterization of adsorbed species on catalysts and which have been central to the discussion of this symposium. These are the extent to which the neutron scattering technique can be used to determine 1) the orientation and position of an adsorbed molecule and 2) the strength and location of the forces bonding a molecule to a surface. 

Other materials which have been characterized by inelastic neutron scattering include silver A and 13X zeolites. Measurements of the scattering from ethylene-H4 and its partially deuteriated derivatives adsorbed by silver 13X zeolite have revealed all the three molecular librations. These were assigned to their respective axes from the deuteriation shifts.87... 

Volume 50 of Advances in Catalysis, published in 2006, was the hrst of a set of three focused on physical characterization of solid catalysts in the functioning state. This volume is the second in the set. The hrst four chapters are devoted to vibrational spectroscopies, including Fourier transform infrared (Lamberti et al.), ultraviolet Raman (Stair), inelastic neutron scattering (Albers and Parker), and infrared-visible sum frequency generation and polarization-modulation infrared rehection absorption (Rupprechter). Additional chapters deal with electron paramagnetic resonance (EPR) (Bruckner) and Mossbauer spectroscopies (Millet) and oscillating microbalance catalytic reactors (Chen et al.). 

Inelastic neutron scattering studies have shown [7-11] that many hydrogen-bonded crystals [potassium carbonate (i.e., KHCO3), various polyanilines, Ca(OH)2, and others] are characterized by the proton dynamics that is very decoupled from the backbone lattice. 

Inelastic neutron scattering spectroscopy is characterized by completely different intensities because the neutron scattering process is entirely attributable to nuclear interactions [110] Each atom features its nuclear cross section, which is independent of its chemical bonding. Then the intensity for any transition is simply related to the atomic displacements scaled by scattering cross sections. And because the cross section of the proton is about one order of magnitude greater than that for any other atom, the method is able to record details of quantum dynamics of proton transfer. 

There have been several reports (Boolchand et al., 1999) on glassforming liquids to show that a transition from floppy to rigid states as a function of composition is associated with discontinuities in one or the other properties of the system. These experiments inelude inelastic neutron scattering to characterize the floppy modes, Lamb-Mossbauer factors,... 

M. Lacroix, H. Jobic, C. Dumonteil, P. Afanasiev, M. Breysse S. Kasztelan (1996). Stud. Surf. Sci. Catal. Part A B., 101, 117-126, Role of adsorbed hydrogen species on ruthenium and molybdenum sulfides. Characterization by inelastic neutron scattering, thermoanalysis methods and model reactions. 

H. Jobic, M. Lacroix, T. Decamp M. Breysse (1995). J. Catal., 157, 414—422. Characterization of ammonia adsorption on ruthenium sulfide. Identification of amino species by inelastic neutron scattering. 

Characterize the mobile hydrogen in NaAlH4 by solid state NMR spectroscopy, inelastic neutron scattering, optical spectroscopy and neutron diffraction studies. 

In this section, experimental techniques for the characterization of zeolites and adsorbate/zeolite samples via IR spectroscopy, Raman scattering and inelastic neutron scattering will be briefly discussed. For more detailed information, the reader is referred to Refs. [145-150]. 

Infrared spectroscopy was amongst the first physico-chemical methods applied in zeolite research. Thus, the first Chapter, Vibrational Spectroscopy , hy H.G. Karge and E. Geidel, covers the application of IR spectroscopy for molecular sieves characterization with and without probe molecules, including also Raman spectroscopy and inelastic neutron scattering as well as a rather detailed theoretical treatment of vibrational spectroscopy as far as it is employed in zeolite research. 

Inelastic neutron scattering (INS) is another technique that has been used for the characterization of surface hydroxyls, but the number ofpubfications is hmited (69—72). Information on the hydroxyl coverage can also be... 

In the RSb manifest crystal-field effects have been observed. They were among the first compounds to be investigated (Liithi et al. 1973b, Mullen et al. 1974). The RSb compounds are well characterized substances with rather small electrical conductivities (Hulliger 1979). The crystal-field splittings have been determined by inelastic neutron scattering spectroscopy (Birgeneau et al. 1973). Therefore, crystal-field effects in the elastic constants have been measured and interpreted quantitatively. 

Quasi-elastic Neutron Scattering. Coherent and incoherent inelastic neutron scattering are unique experimental techniques to characterize molecular motions on a time scale between 10 and 10 s. The continued development of high resolution inelastic scattering techniques in the past two decades (157-159) enables measurement of the dynamic structure factor S(Q, co) and the... 

We restrict the attention to periodic solids, molecular crystals. The excitations are characterized by wave vectors q, that lie in the first Brillouin zone of the lattice considered. These excitations are not necessarily pure translational phonons, librons or vibrons, in general they will be mixed. Much experimental information has been collected about such excitations, by infrared and Raman spectroscopy and, in particular, by inelastic neutron scattering. Due to the optical selection rules infrared and Raman spectra can only probe the = 0 excitations. By neutron scattering one can excite states of any given q and thus measure the complete dispersion (wave vector dependence) of the phonon and vibron frequencies. 

---