- Browse by Author

### Browsing by Author "Kirstein, O"

Now showing 1 - 20 of 32

###### Results Per Page

###### Sort Options

- ItemAb initio phonon dispersion curves used to check experimentally determined elastic constants of the MAX phase Ti3SiC2(Trans. Tech Publication Inc., 2011-07-04) Kirstein, O; Zhang, JF; Kisi, EH; Riley, DP
Show more The ternary carbide Ti3SiC2 is the archetype of MAX phases. To date, MAX phases have proven difficult to synthesize as sufficiently large single crystals from which single crystal elastic constants might be obtained. Therefore, the elastic properties not only of Ti3SiC2 but other MAX phases are extensively studied by ab initio methods. Recently single crystal elastic constants were experimentally determined for the first time using neutron diffraction. The experiment revealed extreme shear stiffness which is not only quite rare in hexagonal materials but also strongly contradicts the predictions of all published MAX phase elastic constants from ab initio calculations. In the present paper we would like to show that such shear stiffness can possibly be supported by ab initio calculations and the calculated phonon dispersion along high symmetry directions.© 2011, Trans Tech PublicationsShow more - ItemAn assessment of the effect of cutting welded samples on residual stress measurements by chill modelling(SAGE Publications, 2010-08-01) Law, M; Kirstein, O; Luzin, V
Show more In making residual stress measurements in welds, a common problem is that the samples are often cut before measurement, which may alter the stresses. To estimate the effects of cutting, a simplified method of modelling residual stresses in welds was developed, known as chill modelling, which requires limited material data and no welding process data. The method can be performed with elastic finite element analysis. The method does not predict the value of the stresses, just the relative reduction that occurs after cutting. The method was validated against published synchrotron measurements of welded plates, which were cut and remeasured a number of times. For welded plates only, an empirical equation was developed that predicts the change in stress after cutting. © 2010, SAGE PublicationsShow more - ItemBragg-edge elastic strain tomography(Engineers Australia, 2017-11-27) Wensrich, CM; Gregg, AWT; Hendriks, JN; Aggarwal, R; Tremsin, AS; Shinohara, T; Luzin, V; Meylan, MH; Kisi, EH; Kirstein, O
Show more Time-of-flight neutron imaging has now progressed to the point where high-resolution energy-resolved imaging is possible. Among many other applications, this technology allows the imaging of elastic strain fields within polycrystalline solids using a geometry identical to a traditional radiograph. 3D strain tomography from measurements such as these has been a current topic of research over the past decade. The authors recently solved this tomography problem and provided a reconstruction algorithm for the set of all systems subject to external loads in the absence of residual or eigenstrain. In this paper we provide an overview of the recent experiment carried out at the J-PARC pulsed neutron source in Japan focused on demonstrating this algorithm. This now represents the first-ever practical demonstration of Bragg-edge neutron transmission strain tomography in a non-axisymmetric system. The results of the experiment are presented along with the validation of the reconstructed field through Digital Image Correlation and traditional constant wavelength neutron strain scanning within the Australian Centre for Neutron Scattering at ANSTO. An outlook on potential strategies for reconstruction in the general case is also provided. © 2017 Engineers AustraliaShow more - ItemBragg-edge neutron strain imaging and tomography(Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-18) Wensrich, C; Gregg, AWT; Hendriks, JN; Luzin, V; Shinohara, T; Kirstein, O; Meylan, MH; Kisi, EH
Show more For more than 10 years, time-of-flight detectors at pulsed neutron sources have been capable of providing high-resolution images of strain fields through Bragg-edge analysis [1]. With a geometry akin to a traditional radiograph, these images represent a projection of the full 3D tensor strain distribution to a scalar field. This poses a rich tomography problem based on a generalised version of the Radon transform known as the Longitudinal Ray Transform (LRT). The solution to this Bragg-edge strain tomography problem promises a new approach by which the full triaxial elastic strain (and hence stress) distribution could be observed within crystalline solids over the scale of centimetres. This presentation will provide an overview of Bragg-edge imaging and strain measurement before outlining recent work by the Authors focused on solving the associated tomography problem. The central issue that rendered the problem ill-posed will be discussed before introducing a range of approaches based on equilibrium constraints. A two dimensional experimental demonstration based on data from the RADEN energy-resolved imaging instrument (at J-PARC in Japan) will be presented with comparisons to detailed constant wavelength strain scans from the KOWARI diffractometer (ANSTO). The generalisation of this approach to three-dimensions will also be discussed. [1] Tremsin et al. “High-resolution strain mapping through time-of-flight neutron transmission diffraction with a microchannel plate neutron counting detector”, Strain, v48 pp296-305, 2012. © The AuthorsShow more - ItemCharacterization of the residual strains in iterative laser forming(Elsevier, 2012-01-01) Knupfer, SM; Paradowska, AM; Kirstein, O; Moore, AJ
Show more In laser forming, thermally induced strains transverse to the laser scan line vary with depth in the material and contribute most significantly to the desired deformation. The through-thickness transverse residual strain distribution was measured by neutron diffraction in laser-formed low carbon steel and aluminium alloy specimens. The specimens were formed with a wide range of laser line energies covering the temperature gradient mechanism (TGM) and shortening or upsetting mechanism (SM), and for single and multi-pass forming (up to 3 laser passes). Below the saturation line energy where the TGM dominates, the gradient of the through-thickness strain distribution was found to increase with increasing line energy and number of laser passes; the gradient decreased again at line energies above the saturation line energy where the efficiency of the TGM decreases. Iterative laser forming can be applied to reduce weld-induced distortions. The peak longitudinal strain measured in the weld seam of a specimen that had been straightened by iterative laser forming was also significantly reduced.(C) 2011 Elsevier B.V.Show more - ItemComparative study between FEA, trepanning and neutron strain diffraction on residual stresses in flash-butt welded rails(Taylor & Francis, 2007-06) Tawfik, D; Mutton, PJ; Kirstein, O; Chiu, WK
Show more This paper compares three independent methods for deriving the residual stresses distribution in AS60 normal cooled flash-butt welded rail. A numerical technique utilised a sequentially coupled thermo-mechanical analysis with representative temperature dependent and phase transformation properties of the rail steel. The numerical model also incorporated an element removal regime to assess the effect of stress relaxation when slicing a plate section from a welded rail section for neutron stress mapping. Two experimental techniques were used to quantify the magnitude of residual stresses in the weld; these were strain gauging and trepanning, and neutron diffraction (ND). The results showed satisfactory correlation between the residual stress distribution obtained from the numerical analysis and the strain gauge/trepanning data and ND stress mapping, respectively. The ND and numerical analysis both confirmed that the tensile residual stresses in both vertical and longitudinal directions are concentrated in the web region, despite a significant relaxation as a result of the sectioning method used to obtain the plate section for neutron stress mapping. © 2007, Taylor & Francis Ltd.Show more - ItemEffect of residual stress on the integrity of a branch connection(Elsevier Science Ltd, 2012-08-01) Law, M; Kirstein, O; Luzin, V
Show more A new connection to an existing gas pipeline was made by hot-tapping, welding directly onto a pressurised pipeline. The welds were not post-weld heat treated, causing significant residual stresses. The critical weld had residual stresses determined by neutron diffraction using ANSTO's residual stress diffractometer, Kowari. The maximum measured residual stress (290 MPa) was 60% of the yield strength. The magnitudes of errors from a number of sources were estimated. An integrity assessment of the welded branch connection was performed with the measured residual stress values and with residual stress distributions from the BS 7910 and API 579 analysis codes. Analysis using estimates of residual stress from API 579 overestimated the critical crack size. © 2012, Elsevier Ltd.Show more - ItemEffects of cutting and specimen size on neutron measurement of residual stresses(Insitute of Physics, 2010-12-16) Law, M; Luzin, V; Kirstein, O
Show more To perform neutron residual stress measurements it is often necessary to cut samples to a manageable size. The effects of cutting a girth welded pipe were investigated with analytical methods and finite element analysis. The effect of cutting on measured stresses was calculated. A simplified method of modelling residual stresses in welds, "chill modelling", is introduced. In ring slitting a cut is made in the axial direction and the deformation is maeesured. The change in elastic stress can be calculated and added to neutron diffraction measurements made on a cut ring to calculate the original stresses. Residual stress measurements were performed to validate the ring slitting correction using ANSTO's residual stress diffractometer Kowari. © 2010, Insitute of Physics.Show more - ItemElastic constants of oriented Ti3AlC2 and Ti3SiC2 obtained via coherent inelastic neutron scattering(International Conference on Neutron Scattering, 2017-07-12) Kirstein, O; Gray, V; Stampfl, APJ; Kisi, EH
Show more Effort has gone into understanding the properties of MAX phases and their archetypes, Ti3SiC2,and Ti3AlC2, is as these materials exhibit a desirable combination of metallic and ceramic properties [1]. Single crystal elastic constants(SEC), usually obtained using ab-initio calculations in combination with crystallographic information, indicate the materials to be isotropic [2]. While it is difficult to obtain single crystals it is possible to produce highly textured specimens. Using a method developed by Buchenau [3] allows using coherent inelastic neutron scattering to obtain an estimation of the SEC, and such an experiment was performed using the three-axis spectrometer TAIPAN at ANSTO [4]. Results for Ti3AlC2 agree with ab-initio calculations and the assumption of isotropy. For Ti3SiC2 experimental results of c44 = 402.7 GPa do not support isotropic values obtained from ab-initio calculations. Molecular dynamics simulations combined with inelastic neutron scatteringexperiments support the initial diffraction experiment and hence themicromechanical model that was used [5]. We present here a self-consistentdescription of the mechanical properties of the MAX phases Ti3SiC2and Ti3AlC2. [1] M. W. Barsoum et al. Annual Rev.Mat. Res. 41(2011); [2] M. F. Cover et al., J. Phys.Conds. Matt., 21(2009) 305403; [3] U. Buchenau, Sol. St. Comm.,Vol.32(12), 1979 ; [4] V. Gray et al.. J. Am. Ceram. Soc.1-6, 2016; [5] E.H. Kisi et al, J. of Phys.: Cond.Matter 22 (2010) 162202Show more - ItemEvaluation of residual stress in SPR joint by neutron diffraction(Trans Tech Publication Inc., 2012-01-01) Haque, R; Beynon, JH; Kirstein, O; Wong, YC; Durandet, Y
Show more The feasibility of measuring residual stresses in Self-Pierce Riveted (SPR) joints by neutron diffraction was evaluated in this study. Despite the small dimensions involved, meaningful results were obtained. It was observed that residual stress in the rivet head was higher in the centre and lower at the edge. For the SPR joints examined, the maximum value of residual stress evaluated was 550MPa, compressive and occurred in the rivet leg. Stresses in material adjacent to the rivet wall and at a distance of three times the rivet radius from the rivet axis were not significant. The results are discussed with respect to the physical events involved during SPR. © 2011, Trans Tech PublicationsShow more - ItemEvaluation of residual stresses in electron-beam welded Zr2.5Nb0.9Hf Zircadyne flange mock-up of a reflector vessel beam tube flange(Elsevier Science BV., 2013-07-01) Muránsky, O; Holden, TM; Kirstein, O; James, JA; Paradowska, AM; Edwards, L
Show more The dual-phase alloy Zr2.5Nb alloy is an important nuclear material, because of its use in current and possible use in future nuclear reactors. It is, however, well-known that Zr2.5Nb weldments can fail through a time-dependent mechanism called delayed hydride cracking which is typically driven by the presence of tensile residual stresses. With a view to understanding the development of residual stresses associated with Zr2.5Nb welds the current study focuses on the evaluation of the residual stresses in a mock-up of a reactor beam tube flange made from Zr2.5Nb0.9Hf. The present results suggests that, like ferritic welds which undergo a solid-state phase transformation upon welding, Zr2.5Nb0.9Hf welds also develop high tensile residual stresses in the heat-affected zone whereas the stresses closer to the weld tip are reduced by the effects of the beta -> alpha solid-state phase transformation. © 2013, Elsevier Ltd.Show more - ItemFeasibility of measuring residual stress profile in different self-pierce riveted joints(Maney Publishing, 2012-01-01) Haque, R; Beynon, JH; Durandet, Y; Kirstein, O; Blacket, S
Show more The feasibility of measuring residual stresses in self-pierce riveted (SPR) joints by neutron diffraction technique was investigated. The main challenge involved dealing with the very small dimensions of SPR joints. Two different joints were examined: aluminium‐steel and steel‐steel. Even though small dimensions were involved, meaningful results were obtained. In the rivet head, tensile stress was observed for the steel‐steel sample, whereas only compressive stress was observed for the aluminium‐steel. The residual stress in the rivet head was higher at the centre and lower at the edge for both joints. Stresses in the sheet material beside the rivet wall and at a distance of three times the rivet radius from the rivet axis were not significant. For the SPR joints examined, the maximum value of residual stress was compressive and occurred in the rivet leg. The results are discussed according to the physical events involved during the process.© 2012, Maney PublishingShow more - ItemForce chains in monodisperse spherical particle assemblies: three-dimensional measurements using neutrons(American Physical Society, 2014-10-03) Wensrich, CM; Kisi, EH; Luzin, V; Garbe, U; Kirstein, O; Smith, AL; Zhang, JF
Show more The full triaxial stress state within individual particles in a monodisperse spherical granular assembly has been measured. This was made possible by neutron imaging and computed tomography combined with neutron diffraction strain measurement techniques and associated stress reconstruction. The assembly in question consists of 549 precision steel ball bearings under an applied axial load of 85 MPa in a cylindrical die. Clear evidence of force chains was observed in terms of both the shape of the probability distribution function for normal stresses and the network formed by highly loaded particles. An extensive analysis of the source and magnitude of uncertainty in these measurements is also presented.©2014 American Physical Society.Show more - ItemFrom single grains to texture(Wiley-VCH Verlag GmbH & Co. KGaA, 2009-10) Yan, K; Liss, KD; Garbe, U; Daniels, JE; Kirstein, O; Li, HJ; Dippenaar, RJ
Show more Structural materials, such as metals, ceramics, and their composites are most often polycrystalline. The nature, morphology, and composition of their microstructure determine in large measure the mechanical properties of the final product, and the art to design novel materials is to find particular arrangements which make them harder, more shock absorbing, heat resistant, or self-recovering upon damage and aging. The understanding of the basic processes and their interplay in a polycrystalline structure are most important for improved simulation of plastic deformation and to predict their thermo-mechanical behavior. © 2009, Wiley-VCH Verlag GmbH & Co. KGaAShow more - ItemThe instrument suite of the European Spallation Source(Elsevier B. V., 2020-01-10) Andersen, KH; Argyriou, DN; Jackson, AJ; Houston, J; Henry, PF; Deen, PP; Toft-Petersen, R; Beran, P; Strobl, M; Arnold, T; Wacklin-Knecht, H; Vivanco, R; Parker, SF; Gussen, A; Kanaki, K; Scionti, G; Olsen, MA; Arai, M; Schmakat, Ph; Lechner, RE; Niedermayer, Ch; Schneider, H; Zanetti, M; Petrillo, C; Moreira, FY; Stepanyan, S; Luna, P; Calzada, E; Stahn, J; Voigt, J; Dupont, T; Hanslik, R; Siemers, DJ; Udby, L; Chowdhury, MAH; Klauser, Ch; Rouijaa, M; Lehmann, E; Heynen, A; Bustinduy, I; Schwaab, A; Raspino, D; Scatigno, C; del Moral, OG; Kiehn, R; Aprigliano, G; Zanatta, M; Huerta, M; Bellissima, S; Lerche, M; Holm-Dahlin, S; Huerta, M; Christensen, NB; Lohstroh, W; Gorini, G; Fenske, J; Hansen, UB; Klauser, C; Rodrigues, S; Müller, M; Gorini, G; Bovo, C; Hall-Wilton, R; Fabrèges, X; Siemers, DJ; Khaplanov, A; Tsapatsaris, N; Taylor, J; Christensen, M; Schefer, J; Woracek, R; Tozzi, P; Müller, M; Carlsen, H; Olsen, MA; Orecchini, A; Di Fresco, L; Paciaroni, A; Bovo, C; Magán, M; Hauback, BC; Elmer, J; Heenan, RK; Piscitelli, F; Masi, F; Bakedano, G; Klimko, S; De Bonis, A; Fedrigo, A; Lukáš, P; Frielinghaus, H; Stahn, J; Schweika, W; Markó, M; Pfeiffer, D; Kirstein, O; Di Fresco, L; Schreyer, A; Orszulik, A; Nowak, G; Butterweck, S; Šaroun, J; Paciaroni, A; Kolevatov, R; Lehmann, EH; Filges, U; Schreyer, A; Koenen, M; Bustinduy, I; Magán, M; Feygenson, M; Cooper, JFK; Abad, E; Senesi, R; Longeville, S; Llamas-Jansa, I; Schulz, M; Birk, JO; Sharp, M; Galsworthy, P; Šaroun, J; Martínez, J; Hiess, A; Holm-Dahlin, S; Filges, U; Pullen, SA; Guyon Le Bouffy, J; Schefer, J; Lukáš, P; Udby, L; Kozielewski, T; Niedermayer, C; Sacchetti, F; Hartl, M; Jaksch, S; Salhi, Z; Brückel, T; Aguilar, J; Aguilar, J; Seifert, M; Bordallo, HN; Robillard, T; Villacorta, FJ; Herranz, I; del Rosso, L; Hauback, BC; Orecchini, A; Fabrèges, G; Fenske, J; Neuhaus, J; Schillinger, B; Abad, E; Kittelmann, T; Lefmann, K; Seifert, M; Neuhaus, J; Herranz, I; Kolevatov, R; Annighöfer, B; Oksanen, E; Morgano, M; Laszlo, G; Freeman, PG; Kennedy, SJ; Bertelsen, M; Bellissima, S; Alba-Simionesco, C; Markó, M; Mezei, F; Chowdhury, M; Halcrow, W; Jestin, J; Lieutenant, K; Babcock, E; Rønnow, HM; Engels, R; del Moral, OG; Vickery, A; Rouijaa, M; Lavie, P; Petersson Årsköld, S; Glavic, A; Désert, S; Mannix, D; Scatigno, C; Petry, W; Christensen, NB; Violini, N; Villacorta, FJ; Porcher, F; Glavic, A; Scionti, G; Zanetti, M; Fernandez-Alonso, F; Rønnow, HM; Mosconi, M; Olsson, M; Stepanyan, S; Petrillo, C; del Rosso, L; Harbott, P; Sacchetti, F; Bertelsen, M; Kämmerling, H; Andreani, C; Schulz, M; Colognesi, D; Luna, P; Loaiza, L; Turner, D; Martínez, JL; Tartaglione, A; Sordo, F; Llamas-Jansa, I; Schmakat, P; Lechner, RE; Poqué, A; Fernandez-Alonso, F; Colognesi, D; Tartaglione, A; Morgano, M; Webb, N; Loaiza, L; Whitelegg, L; Petry, W; Iversen, K; Vivanco, R; Tozzi, P; Goukassov, A; Schillinger, B; Carlsen, H; Masi, F; Christensen, M; Nowak, G; Nightingale, J; Schütz, S; Lopez, CI; Langridge, S; Schütz, S; Nagy, G; Zanatta, M; Andreani, C; Lefmann, K; Lohstroh, W; Mosconi, M; Senesi, R; Stefanescu, I; Bakedano, G; Hagen, ME; Wischnewski, A; Bourges, P; Hansen, UB; De Bonis, A; Kiehn, R; Parker, SF; Iversen, K; Sordo, F; Freeman, PG; Birk, JO; Rodríguez, DM; Ansell, S
Show more An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact of the early years of the ESS, and provide a solid base for completion and further expansion of the facility. © 2020 The Authors. Published by Elsevier B.V. Open access article under the CC BY-NC-ND license.Show more - ItemKowari - OPAL's new stress diffractometer for the engineering community: capabilities and first results(Trans Tech Publications, 2009-11-10) Kirstein, O; Garbe, U; Luzin, V
Show more Kowari is a neutron diffractometer at ANSTO’s research reactor OPAL. The instrument is dedicated to investigate residual strains and stresses in engineering samples or new materials. Besides its usage in engineering/strain-scanning it is more and more frequently being used for obtaining texture information related to materials science applications. In particular the possibility of using the gauge volume defining slit systems allows extracting local information from the diffraction peak, i.e. position, intensity, and width, without the need to cut the sample specimen. The instrument obtained its operating license in August 2008 to briefly describe the instruments parameters and capabilities, and give examples of two typical applications since it went from commissioning into user mode. © 2020 by Trans Tech Publications LtdShow more - ItemMeasurement and analysis of the stress distribution during die compaction using neutron diffraction(Springer, 2012-11-01) Wensrich, CM; Kisi, EH; Zhang, JF; Kirstein, O
Show more The full axisymmetric stress state of a granular material undergoing compaction in a cylindrical die has been measured using a technique based on neutron powder diffraction. This technique allowed the detailed distribution of stress to be measured in situ, deep within a copper powder inside a solid die. Four components of normal strain were measured over a radial cross section. These components consisted of the axial, radial, hoop and an off-axis strain in the axial-radial direction. This allowed for the reconstruction of the full axisymmetric stress tensor as a distribution over the radial cross section. Many interesting features were observed in this distribution, such as exponential decay of the axial stress (described by Janssen in Zeitschrift des Vereines duetscher Ingenieure 39:1045, 1895), and highly localised regions of high shear stress. The potential of this type of data in the validation of numerical models is discussed. © 2012, Springer.Show more - ItemMeasurement of residual stress in a welded branch connection and effects on fracture behaviour(Insitute of Physics, 2010-12-16) Law, M; Luzin, V; Kirstein, O
Show more The branch analysed in this paper was not post weld heat treated, resulting in significant residual stresses. Assessment codes assume these to be at, or close to, yield. An integrity assessment of a welded branch connection was carried out using these high assumed residual stresses. The weld then had residual stresses determined by neutron diffraction, performed using ANSTO's residual stress diffractometer, Kowari. The maximum measured residual stress (290 MPa or 60% of yield) was much lower than the yield value assumed by assessment codes. Reanalysing with the actual residual stresses almost doubled the critical crack size, increasing the safety of the connection. © 2010, Insitute of Physics.Show more - ItemQuantitative neutron diffraction texture measurement applied to alpha-phase alumina and Ti(3)AlC(2)(Wiley-Blackwell, 2011-10-01) Zhang, JF; Kisi, EH; Kirstein, O
Show more Orientation distribution functions, essential for making a quantitative connection between single-crystal and polycrystal properties, have been determined for extruded [alpha]-phase alumina, hot-pressed Ti3AlC2 and cold isostatically pressed Ti3AlC2 using experimental pole figures recorded on the fixed-wavelength neutron diffractometer KOWARI. Some practical improvements to the calculation of the pole-figure density from the raw area-detector data, and for constructing pole figures on an n x ndegrees hemispherical grid, are presented. The textures give some insight into particle flow during manufacture. Directly measured material textures were compared with one-dimensional pole density functions, such as the March and Rietveld functions commonly used for the correction of preferred orientation in Rietveld refinements, as a means of assessing the utility of the latter for the computation of diffraction elastic constants and other polycrystal properties from a given set of single-crystal properties. © 2011, Wiley-BlackwellShow more - ItemQuasi-elastic neutron spectroscopy and rotational potentials of methyl halides(Elsevier B. V., 2006-11-15) Kirstein, O; Prager, M; Grimm, H; Buchsteiner, A; Wischnewski, A
Show more The methyl halides belong to the simplest organic molecules that contain CH3 groups. The lattice dynamics of these molecules were modeled recently based on the exact crystallographic structure and transferable pair potential parameters. Experiments were done using the NEAT spectrometer at BENSC, HMI, Germany and the BSJ spectrometer at FZJ, Germany to obtain values for the individual activation energy. The experimental values for the activation energies were used to refine the Fourier parameters of the individual rotational potential. Experimentally determined activation energies for all molecules, but the methyl fluoride, agree with single particle model predictions. Crown Copyright © 2006 Published by Elsevier B.V.Show more