1
|
Nag P, Ranković M, Polášek M, Čurík R, Slaughter DS, Fedor J. Contrasting Dynamics in Isoelectronic Anions Formed by Electron Attachment. J Phys Chem Lett 2024; 15:895-902. [PMID: 38241169 PMCID: PMC10839900 DOI: 10.1021/acs.jpclett.3c03460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2023] [Revised: 01/09/2024] [Accepted: 01/12/2024] [Indexed: 01/21/2024]
Abstract
Cyanogen NCCN and cyanoacetylene HCCCN are isoelectronic molecules, and as such, they have many similar properties. We focus on the bond cleavage in these induced by the dissociative electron attachment. In both molecules, resonant electron attachment produces CN- with very similar energy dependence. We investigate the very different dissociation dynamics, in each of the two molecules, revealed by velocity map imaging of this common fragment. Different dynamics are manifested both in the excess energy partitioning and in the angular distributions of fragments. Based on the comparison with electron energy loss spectra, which provide information about possible parent states of the resonances (both optically allowed and forbidden excited states of the neutral target), we ascribe the observed effect to the distortion of the nuclear frame during the formation of core-excited resonance in cyanoacetylene. The proposed mechanism also explains a puzzling difference in the magnitude of the CN- cross section in the two molecules which has been so far unexplained.
Collapse
Affiliation(s)
- P. Nag
- J.
Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech
Republic
| | - M. Ranković
- J.
Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech
Republic
| | - M. Polášek
- J.
Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech
Republic
| | - R. Čurík
- J.
Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech
Republic
| | - D. S. Slaughter
- Chemical
Sciences Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720, United States
| | - J. Fedor
- J.
Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech
Republic
| |
Collapse
|
2
|
Siddiqui KM, Durham DB, Cropp F, Ji F, Paiagua S, Ophus C, Andresen NC, Jin L, Wu J, Wang S, Zhang X, You W, Murnane M, Centurion M, Wang X, Slaughter DS, Kaindl RA, Musumeci P, Minor AM, Filippetto D. Relativistic ultrafast electron diffraction at high repetition rates. Struct Dyn 2023; 10:064302. [PMID: 38058995 PMCID: PMC10697722 DOI: 10.1063/4.0000203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Accepted: 11/08/2023] [Indexed: 12/08/2023]
Abstract
The ability to resolve the dynamics of matter on its native temporal and spatial scales constitutes a key challenge and convergent theme across chemistry, biology, and materials science. The last couple of decades have witnessed ultrafast electron diffraction (UED) emerge as one of the forefront techniques with the sensitivity to resolve atomic motions. Increasingly sophisticated UED instruments are being developed that are aimed at increasing the beam brightness in order to observe structural signatures, but so far they have been limited to low average current beams. Here, we present the technical design and capabilities of the HiRES (High Repetition-rate Electron Scattering) instrument, which blends relativistic electrons and high repetition rates to achieve orders of magnitude improvement in average beam current compared to the existing state-of-the-art instruments. The setup utilizes a novel electron source to deliver femtosecond duration electron pulses at up to MHz repetition rates for UED experiments. Instrument response function of sub-500 fs is demonstrated with < 100 fs time resolution targeted in future. We provide example cases of diffraction measurements on solid-state and gas-phase samples, including both micro- and nanodiffraction (featuring 100 nm beam size) modes, which showcase the potential of the instrument for novel UED experiments.
Collapse
Affiliation(s)
- K. M. Siddiqui
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | | | | | - F. Ji
- Accelerator Technology and Applied Physics Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - S. Paiagua
- Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, USA
| | - C. Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - N. C. Andresen
- Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - L. Jin
- Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, USA
| | - J. Wu
- Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, USA
| | - S. Wang
- Department of Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, California 94720, USA
| | - X. Zhang
- Department of Mechanical Engineering, University of California at Berkeley, Berkeley, California 94720, USA
| | - W. You
- Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, USA
| | - M. Murnane
- Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, USA
| | - M. Centurion
- Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - X. Wang
- Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - D. S. Slaughter
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, California 94720, USA
| | | | - P. Musumeci
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | | | - D. Filippetto
- Accelerator Technology and Applied Physics Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| |
Collapse
|
3
|
Iskandar W, Rescigno TN, Orel AE, Severt T, Larsen KA, Streeter ZL, Jochim B, Griffin B, Call D, Davis V, McCurdy CW, Lucchese RR, Williams JB, Ben-Itzhak I, Slaughter DS, Weber T. Efficiency of charge transfer in changing the dissociation dynamics of OD+ transients formed after the photo-fragmentation of D2O. J Chem Phys 2023; 159:094301. [PMID: 37668253 DOI: 10.1063/5.0159300] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Accepted: 08/07/2023] [Indexed: 09/06/2023] Open
Abstract
We present an investigation of the relaxation dynamics of deuterated water molecules after direct photo-double ionization at 61 eV. We focus on the very rare D+ + O+ + D reaction channel in which the sequential fragmentation mechanisms were found to dominate the dynamics. Aided by theory, the state-selective formation and breakup of the transient OD+(a1Δ, b1Σ+) is traced, and the most likely dissociation path-OD+: a1Δ or b1Σ+ → A 3Π → X 3Σ- → B 3Σ--involving a combination of spin-orbit and non-adiabatic charge transfer transitions is determined. The multi-step transition probability of this complex transition sequence in the intermediate fragment ion is directly evaluated as a function of the energy of the transient OD+ above its lowest dissociation limit from the measured ratio of the D+ + O+ + D and competing D+ + D+ + O sequential fragmentation channels, which are measured simultaneously. Our coupled-channel time-dependent dynamics calculations reproduce the general trends of these multi-state relative transition rates toward the three-body fragmentation channels.
Collapse
Affiliation(s)
- W Iskandar
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - T N Rescigno
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - A E Orel
- Chemical Engineering, University of California, Davis, California 95616, USA
| | - T Severt
- J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA
| | - K A Larsen
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Graduate Group in Applied Science and Technology, University of California, Berkeley, California 94720, USA
| | - Z L Streeter
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Chemistry, University of California, Davis, California 95616, USA
| | - B Jochim
- J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA
| | - B Griffin
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
| | - D Call
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
| | - V Davis
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
| | - C W McCurdy
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Chemistry, University of California, Davis, California 95616, USA
| | - R R Lucchese
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - J B Williams
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
| | - I Ben-Itzhak
- J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA
| | - D S Slaughter
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Th Weber
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| |
Collapse
|
4
|
Iskandar W, Rescigno TN, Orel AE, Larsen KA, Griffin B, Call D, Davis V, Jochim B, Severt T, Williams JB, Ben-Itzhak I, Slaughter DS, Weber T. Atomic autoionization in the photo-dissociation of super-excited deuterated water molecules fragmenting into D + + O + + D. Phys Chem Chem Phys 2023; 25:21562-21572. [PMID: 37545426 DOI: 10.1039/d3cp02438e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/08/2023]
Abstract
We present the relaxation dynamics of deuterated water molecules via autoionization, initiated by the absorption of a 61 eV photon, producing the very rare D+ + O+ + D breakup channel. We employ the COLd target recoil ion momentum spectroscopy method to measure the 3D momenta of the ionic fragments and emitted electrons from the dissociating molecule in coincidence. We interpret the results using the potential energy surfaces extracted from multi-reference configuration interaction calculations. The measured particle energy distributions can be related to a super-excited monocationic state located above the double ionization threshold of D2O. The autoionized electron energy shows a sharp distribution centered around 0.5 eV, which is a signature of the atomic oxygen autoionization occurring in the direct and sequential dissociation processes of D2O+* at a large internuclear distance. In this way, an O+ radical fragment and a low-energy electron are created, both of which can trigger secondary reactions in their environment.
Collapse
Affiliation(s)
- W Iskandar
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA-94720, USA.
| | - T N Rescigno
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA-94720, USA.
| | - A E Orel
- Department of Chemical Engineering, University of California, Davis, CA-95616, USA
| | - K A Larsen
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA-94720, USA.
- Graduate Group in Applied Science and Technology, University of California, Berkeley, CA-94720, USA
| | - B Griffin
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA-94720, USA.
- Department of Physics, University of Nevada, Reno, NV-89557, USA
| | - D Call
- Department of Physics, University of Nevada, Reno, NV-89557, USA
| | - V Davis
- Department of Physics, University of Nevada, Reno, NV-89557, USA
| | - B Jochim
- J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS-66506, USA
| | - T Severt
- J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS-66506, USA
| | - J B Williams
- Department of Physics, University of Nevada, Reno, NV-89557, USA
| | - I Ben-Itzhak
- J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS-66506, USA
| | - D S Slaughter
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA-94720, USA.
| | - Th Weber
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA-94720, USA.
| |
Collapse
|
5
|
Slaughter DS, Weber T, Belkacem A, Trevisan CS, Lucchese RR, McCurdy CW, Rescigno TN. Selective bond-breaking in formic acid by dissociative electron attachment. Phys Chem Chem Phys 2020; 22:13893-13902. [PMID: 32542241 DOI: 10.1039/d0cp01522a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report the results of a joint experimental and theoretical study of dissociative electron attachment to formic acid (HCOOH) in the 6-9 eV region, where H- fragment ions are a dominant product. Breaking of the C-H and O-H bonds is distinguished experimentally by deuteration of either site. We show that in this region H- ions can be produced by formation of two or possibly three Feshbach resonance (doubly-excited anion) states, one of which leads to either C-H or O-H bond scission, while the other can only produce formyloxyl radicals by O-H bond scission. Comparison of experimental and theoretical angular distributions of the anion fragment allows the elucidation of state specific pathways to dissociation.
Collapse
Affiliation(s)
- D S Slaughter
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
| | | | | | | | | | | | | |
Collapse
|
6
|
Larsen KA, Cryan JP, Shivaram N, Champenois EG, Wright TW, Ray D, Kostko O, Ahmed M, Belkacem A, Slaughter DS. VUV and XUV reflectance of optically coated mirrors for selection of high harmonics. Opt Express 2016; 24:18209-18216. [PMID: 27505785 DOI: 10.1364/oe.24.018209] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We report the reflectance, ~1° from normal incidence, of six different mirrors as a function of photon energy, using monochromatic vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) radiation with energies between 7.5 eV and 24.5 eV. The mirrors examined included both single and multilayer optical coatings, as well as an uncoated substrate. We discuss the performance of each mirror, paying particular attention to the potential application of suppression and selection of high-order harmonics of a Ti:sapphire laser.
Collapse
|
7
|
Sturm FP, Wright TW, Ray D, Zalyubovskaya I, Shivaram N, Slaughter DS, Ranitovic P, Belkacem A, Weber T. Time resolved 3D momentum imaging of ultrafast dynamics by coherent VUV-XUV radiation. Rev Sci Instrum 2016; 87:063110. [PMID: 27370429 DOI: 10.1063/1.4953441] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2016] [Accepted: 05/25/2016] [Indexed: 06/06/2023]
Abstract
We present a new experimental setup for measuring ultrafast nuclear and electron dynamics of molecules after photo-excitation and ionization. We combine a high flux femtosecond vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) source with an internally cold molecular beam and a 3D momentum imaging particle spectrometer to measure electrons and ions in coincidence. We describe a variety of tools developed to perform pump-probe studies in the VUV-XUV spectrum and to modify and characterize the photon beam. First benchmark experiments are presented to demonstrate the capabilities of the system.
Collapse
Affiliation(s)
- F P Sturm
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - T W Wright
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - D Ray
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - I Zalyubovskaya
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - N Shivaram
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - D S Slaughter
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - P Ranitovic
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - A Belkacem
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Th Weber
- Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| |
Collapse
|
8
|
Douguet N, Slaughter DS, Adaniya H, Belkacem A, Orel AE, Rescigno TN. Signatures of bond formation and bond scission dynamics in dissociative electron attachment to methane. Phys Chem Chem Phys 2015; 17:25621-8. [DOI: 10.1039/c5cp04178c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We show that a single T2 resonance can explain the 10 eV dissociative electron attachment peak in methane.
Collapse
Affiliation(s)
- N. Douguet
- Department of Chemical Engineering and Materials Science
- University of California
- Davis
- USA
| | - D. S. Slaughter
- Chemical Sciences Division
- Lawrence Berkeley National Laboratory
- Berkeley
- USA
| | - H. Adaniya
- Chemical Sciences Division
- Lawrence Berkeley National Laboratory
- Berkeley
- USA
| | - A. Belkacem
- Chemical Sciences Division
- Lawrence Berkeley National Laboratory
- Berkeley
- USA
| | - A. E. Orel
- Department of Chemical Engineering and Materials Science
- University of California
- Davis
- USA
| | - T. N. Rescigno
- Chemical Sciences Division
- Lawrence Berkeley National Laboratory
- Berkeley
- USA
| |
Collapse
|
9
|
Kawarai Y, Weber T, Azuma Y, Winstead C, McKoy V, Belkacem A, Slaughter DS. Dynamics of the Dissociating Uracil Anion Following Resonant Electron Attachment. J Phys Chem Lett 2014; 5:3854-3858. [PMID: 26278760 DOI: 10.1021/jz501907d] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report a combined experimental and theoretical investigation of dissociative electron attachment (DEA) to the nucleobase uracil. Using ion momentum imaging experiments employing a DEA reaction microscope we have measured 3-dimensional momentum distributions of specific anionic fragments following DEA to uracil by 6 eV electrons. From the measured anion fragment kinetic energy we determine the possible dissociation pathways and the total kinetic energy release. We employ electronic structure and electron scattering calculations to determine the probability for electron attachment in the molecular frame. Combining these calculations with the imaging measurements, we reveal several key features of the coupled electronic and nuclear dynamics of DEA.
Collapse
Affiliation(s)
- Y Kawarai
- †Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1, Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan
- ‡Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Th Weber
- ‡Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Y Azuma
- †Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1, Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan
| | - C Winstead
- ¶A. A. Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
| | - V McKoy
- ¶A. A. Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States
| | - A Belkacem
- ‡Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - D S Slaughter
- ‡Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| |
Collapse
|
10
|
Adaniya H, Slaughter DS, Osipov T, Weber T, Belkacem A. A momentum imaging microscope for dissociative electron attachment. Rev Sci Instrum 2012; 83:023106. [PMID: 22380078 DOI: 10.1063/1.3685244] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We describe an experimental approach to image the three-dimensional (3D) momentum distribution of the negative ions arising from dissociative electron attachment (DEA). The experimental apparatus employs a low energy pulsed electron gun, an effusive gas source and a 4π solid-angle ion momentum imaging spectrometer consisting of a pulsed ion extraction field, an electrostatic lens, and a time- and position-sensitive detector. The time-of-flight and impact position of each negative ion are measured event by event in order to image the full 3D ion momentum sphere. The system performance is tested by measuring the anion momentum distributions from two DEA resonances, namely H(-) from H(2)O(-) ((2)B(1)) and O(-) from O(2)(-) ((2)Π(u)). The results are compared with existing experimental and theoretical data.
Collapse
Affiliation(s)
- H Adaniya
- Lawrence Berkeley National Laboratory, Chemical Sciences, Berkeley, California 94720, USA
| | | | | | | | | |
Collapse
|
11
|
Jones ACL, Caradonna P, Makochekanwa C, Slaughter DS, McEachran RP, Machacek JR, Sullivan JP, Buckman SJ. Observation of threshold effects in positron scattering from the noble gases. Phys Rev Lett 2010; 105:073201. [PMID: 20868040 DOI: 10.1103/physrevlett.105.073201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Indexed: 05/29/2023]
Abstract
Channel coupling is a phenomenon that has been investigated for many scattering processes, and is responsible for the formation of cusps or steps in the cross sections for open scattering channels at, or near, the onset of a new scattering channel. It has long been speculated that the opening of the positronium formation channel may lead to the formation of such cusp features in the elastic positron scattering cross section. In this work, elastic scattering of positrons has been measured in the region of the positronium formation threshold for the noble gases He-Xe. Cusplike behavior is observed and, while the features which are observed appear broad, they represent a magnitude of between 4 and 15% of the total elastic cross section. No evidence is found of any other features in this region, at least within the uncertainty of the present data, discounting the possibility of scattering resonances.
Collapse
Affiliation(s)
- A C L Jones
- ARC Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, Australian National University, Canberra 0200 Australia
| | | | | | | | | | | | | | | |
Collapse
|
12
|
Abstract
The purpose of this study was to assess the effectiveness of a model for teaching problem-solving skills to first-year physical therapy students using the Watson-Glaser Critical Thinking Appraisal (CTA) and participant feedback. We used a pretest-posttest control group design. Subjects were 31 first-year physical therapy students divided into a Control Group (n = 15) and an Experimental Group (n = 16). Students in the Experimental Group used the problem-solving model during a four-week clerkship. No difference was found between the Experimental and Control Groups' performance on the CTA. Subjectively, students in the Experimental Group and their Clinical Instructors found the model to be an effective tool that aided students' understanding of patient assessment and treatment program planning. The need for an objective assessment tool of problem-solving models in physical therapy is discussed.
Collapse
Affiliation(s)
- D S Slaughter
- University of Kentucky Sports Medicine Center, Lexington 40536
| | | | | | | |
Collapse
|