40 research outputs found
CAVITY-ENHANCED PARITY-NONCONSERVING OPTICAL ROTATION IN Hg, Xe, AND I
No full textAuthor Institution: Department of Physics, University of Crete, and Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas 71110 Heraklion-Crete, GreeceAtomic parity-nonconservation (PNC) experiments provide a low-energy test of the Standard Model. However, atomic PNC experiments have proved to be very difficult, typically taking at least 10-20 years to complete. In addition, the measurements of anapole moments in Cs and Tl (the only such measurements to date, performed in the mid 1990s) appear to be inconsistent with each other. Atomic PNC experiments on radioactive isotopes of Fr and Ra are underway at collider facilities (TRIUMF and KVI Groningen, respectively), for which larger experimental signals are expected and several isotopes are available. Here, we describe our recent proposals for the measurement of PNC optical rotation in metastable Hg and Xe [1], and ground state I atoms [2]. A novel optical cavity is proposed which amplifies the optical rotation by about , and allows two signal reversals, therefore allowing room-temperature, table-top PNC experiments with large experimental PNC signals, and rapid signal reversals. We discuss the experimental sensitivity to anapole moments for odd-proton nuclei (in I) and odd-neutron nuclei (in Hg and Xe). \begin{itemize} \item[1] L. Bougas, G. E. Katsoprinakis, W. von Klitzing, J. Sapirstein, and T. P. Rakitzis, Phys. Rev. Lett {\bf 108}, 210801 (2012). \item[2] G. E. Katsoprinakis, L. Bougas, T. P. Rakitzis, V. A. Dzuba and V. V. Flambaum, Phys. Rev. A ({\it submitted}) http://arxiv.org/abs/1301.6947. \end{itemize
Macroscopic production of highly nuclear-spin-polarized molecules from IR-excitation and photodissociation of molecular beams
No full textPure, highly nuclear-spin-polarized molecules have only been produced with molecular beam-separation methods, with production rates up to s^-1. Here, we propose the production of spin-polarized molecular photofragments from the IR-excitation and photodissociation of molecular beams, with production rates approaching the tabletop-IR-laser photon fluxes of s^-1. We give details on the production of spin-polarized molecular hydrogen and water isotopes, from formaldehyde and formic acid beams, respectively. Macroscopic quantities of these molecules are important for NMR signal enhancement, and for the needs of a nuclear fusion reactor, to increase the D-T or D-3He unpolarized nuclear fusion cross section by 50%
Polarization REsearch for Fusion Experiments and Reactors - The PREFER Collaboration: Purposes and Present Status
No full textThe PREFER (Polarization REsearch for Fusion Experiments and Reactors) collaboration aims to address the know–hows in different fields and techniques to the challenging bet on fusion with polarized fuel. The efforts on a variety of duties and goals are shared between different research groups, indicated here by underlining in the authors’ list the scientific responsibles. Starting from still open questions of fusion reaction physics, as for example the study of D+D spin–dependent cross–sections (Vasilyev) to the acceleration of polarized ions from laser-induced plasmas (Büscher), there are many connections between the involved research groups. The collaboration is also tackling the production of nuclear polarized molecules, recombined from a polarized atomic beam (Engels), and its cryogenic condensation and transport (Ciullo). Other options for the production of polarized fuel are investigated in parallel, like spin separation of molecules in polarized molecular beam sources (Toporkov), or via photodissociation of molecules into polarized hydrogen/deuterium atoms (Rakitzis). The status of the different fields under investigation and the connections between these topics and the different research groups will be provided
Development of polarized sources based on molecular photodissociation
No full textMolecular photodissociation is an innovative method for the preparation of polarized atoms andmolecules. It is a fundamental chemical process that involves the absorption of one or morepolarized photons by a molecule including its fragmentation into polarized atomic (or molecular)fragments. Recently, T. P. Rakitzis’ group produced high densities of spin-polarized hydrogenatoms applying molecular photodissociation to hydrogen halides. The obtained densities (10^19cm^−3) and short production times (ns timescales) surpass by several orders of magnitude conven-tional methods such as spin-exchange optical pumping and Stern-Gerlach spin separation. Thesedensity and time regimes make it an ideal candidate for a broad range of applications, e.g., laser-induced acceleration from polarized gas targets and polarized five-nucleon fusion reactions (d-3H,d-3He). The second has been shown to have an increased cross section by ∼50% compared to theunpolarized case. The photodissociation method has been adopted by M. Büscher’s group for theproduction of polarized proton and deuteron beams at the Forschungszentrum Jülich. Here, wereport on the production and detection scheme of these beams
Photochemie kleiner Moleküle
No full textNiederjohann B. Photochemistry of small molecules. Bielefeld (Germany): Bielefeld University; 2004.The dissertation consists of two parts, where part I deals with the realization of the OH+D2 reaction and part II with the dissociation dynamics of iodine molecule above the first ionization limit.
Part I deals with the realization of the OH+D2 to HOD+D reaction. The main issue was to build a source of OH radicals with a sufficient high kinetic energy to overcome the barrier to the reaction of 5.3 kcal/mol. The OH radicals were produced by photolysis of a suitable precursor. Within this work, the OH radicals from two different precursors, H2O2 and HNO3, were studied concerning their rotational and thus their kinetic energy distribution. Also the total amount of OH radicals were compared, regarding the different precursors and also different molecular beam set-ups.
Part II deals with the photodissociation dynamics of the iodine molecule at excitation energies (10.2-20.4eV) above the first ionization threshold (9.31eV). This processes were studied with velocity map imaging, a special form of ion imaging. An analysis of the measured images showed that a variety of different processes were involved, among them production of free ion pair states, neutral dissociation of the iodine molecule and dissociation to a neutral iodine atom and an iodine ion via direct ionization to a repulsive ionic molecular state. A new process was found at excitation energies around 14eV which was attributed to a three-body-process, where the electron can take away a variable amount of kinetic energy, resulting in a very broad kinetic energy distribution of the I and I+ fragments. Coupling of a molecular Rydberg state which converges to a higher lying repulsive state of the iodine ionic molecule to a lower lying repulsive ionic molecular state is supposed to be the key mechanism.
Also a photoelectron spectrum was measured
Development of polarized sources based on molecular photodissociation
No full textMolecular photodissociation is an innovative method for the preparation of polarized atoms and molecules. It is a fundamental chemical process that involves the absorption of one or more polarized photons by a molecule including its fragmentation into polarized atomic (or molecular) fragments. Recently, T. P. Rakitzis’ group produced high densities of spin polarized hydrogen atoms applying molecular photodissociation to hydrogen halides. The obtained densities (10^19 cm^−3) and short production times (ns timescales) surpass by several orders of magnitude conventional methods such as spin-exchange optical pumping and Stern-Gerlach spin separation. These density and time regimes make it an ideal candidate for a broad range of applications, e.g. laser-induced acceleration from polarized gas targets and polarized five-nucleon fusion reactions (D-T, D-3He). The second has been shown to have an increased cross section by ∼50% compared to the unpolarized cas
Transient Kinetics of Protein Modification Reactions by an Unstable Modifying Agent
No full textJournal of Molecular Catalysi
Photofragment alignment in the photodissociation of I-2 from 450 to 510 nm
No full textContains fulltext :
35565.pdf (Publisher’s version ) (Open Access)A combination of velocity map imaging and slicing techniques have been used to measure the product recoil anisotropy and angular momentum polarization for the photodissociation process I-2-> I(P-2(3/2))+I(P-2(3/2)) and I-2-> I(P-2(3/2))+I(P-2(1/2)) in the 450-510 nm laser wavelength region using linearly polarized photolysis and probe laser light. The former channel is produced predominantly via perpendicular excitation to the (1)Pi(u) state, and the latter is predominantly parallel, via the B (3)Pi(0(u))(+) state. In both cases we observe mostly adiabatic dissociation, which produces electronically aligned iodine atoms in the parallel to m parallel to=1/2 states with respect to the recoil direction. (c) 2006 American Institute of Physics
Advantages of nuclear fusion with polarized fuel
No full textThe use of nuclear polarized fuel, i.e. polarized D, T or 3He, for coming fusion reactors promises to increase their energy output and to optimize the complete fusion process in various ways. But before these advantages can be utilized, several questions must be answered and technical issues must be overcome. Among others, the members of the PREFER collaboration started to investigate the different challenges of “polarized fusion”
Photofragment angular momentum distributions in the molecular frame. II. Single state dissociation, multiple state interference, and nonaxial recoil in photodissociation of polyatomic molecules
No full textWe present an aqk(s) polarization-parameter model to describe product angular momentum polarization from the one-photon photodissociation of polyatomic molecules in the molecular frame. We make the approximation that the final photofragment recoil direction is unique and described by the molecular frame polar coordinates (α,φi), for which the axial recoil approximation is a special case (e.g., α = 0). This approximation allows the separation of geometrical and dynamical factors, in particular, the expression of the experimental sensitivities to each of the aqk(s) in terms of the molecular frame polar angles (χi,φi) of the transition dipole moment μi. This separation is applied to the linearly polarized photodissociation of polyatomic molecules (asymmetric, symmetric, and spherical top molecules are discussed) and to all dissociation mechanisms that satisfy our recoil approximation, including those with nonaxial recoil and multiple state interference, giving important insight into the geometrical properties of the photodissociation mechanism. For example, we demonstrate that the ratio of polarization parameters A0k(aniso)/A0k(iso) = β (where β is the spatial anisotropy parameter) is an indication that the dynamics can be explained by a single dissociative state. We also show that for asymmetric top photodissociation, the sensitivity to the a1k(s) parameters, which can arise either from single-surface or multiple-surface interference mechanisms, is nonzero only for components of the transition dipole moments within the v-d plane of the recoil frame
