1,664 research outputs found
Ground-state electric quadrupole moment of 31Al
Ground-state electric quadrupole moment of 31Al (I =5/2+, T_1/2 = 644(25) ms)
has been measured by means of the beta-NMR spectroscopy using a spin-polarized
31Al beam produced in the projectile fragmentation reaction. The obtained Q
moment, |Q_exp(31Al)| = 112(32)emb, are in agreement with conventional shell
model calculations within the sd valence space. Previous result on the magnetic
moment also supports the validity of the sd model in this isotope, and thus it
is concluded that 31Al is located outside of the island of inversion.Comment: 5 page
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Tipping the balance: theoretical interrogation of divergent extended heterolytic fragmentations.
Herein we interrogate a type of heterolytic fragmentation reaction called a 'divergent fragmentation' using density functional theory (DFT), natural bond orbital (NBO) analysis, ab initio molecular dynamics (AIMD), and external electric field (EEF) calculations. We demonstrate that substituents, electrostatic environment and non-statistical dynamic effects all influence product selectivity in reactions that involve divergent fragmentation pathways. Direct dynamics simulations reveal an unexpected post-transition state bifurcation (PTSB), and EEF calculations suggest that some transition states for divergent pathways can, in principle, be selectively stabilized if an electric field of the correct magnitude is oriented appropriately
Synthetic Studies toward Biologically Active Quinones and Alkaloids
Part 1 describes the synthesis and biological evaluation of small-molecule phosphatase inhibitors. The targets for the synthesized compounds are mainly Cdc25 phosphatases, which play a key role in regulating cell cycle and are often over-expressed in cancers. Highlights of the synthesis are the amide bond formation, the synthesis of secondary amines via o-Ns chemistry, the ring opening of the lactam by the amine, the preparation of various (iso)quinolinediones and the substitution reactions of (iso)quinolinediones with amines and thiols. The synthesis and reaction of isoquinonlinediones are particularly highlighted in the total synthesis of caulibugulones A-E. Biological assays established the (iso)quinolinediones as new phosphatase inhibitors with considerable selectivity against the Cdc25 family of DSPases.Part 2 describes the synthetic studies toward the total synthesis of parvistemonine, which represents one of the most challenging synthetic targets among Stemona alkaloids. The studies are mainly focused on the development of a fragmentation strategy aimed at the total synthesis of parvistemonine. Highlights of these studies are the synthesis of vinyl azides, the fragmentation reaction of tertiary alcohols and the use of the trimethylsilyl-methylene group as a directing group in the fragmentation reaction. These studies demonstrate a novel vinylogous azido alcohol fragmentation reaction in simple model systems and a regioselective fragmentation reaction of hydroxy indolines
Shape and structure of N=Z 64Ge; Electromagnetic transition rates from the application of the Recoil Distance Method to knock-out reaction
Transition rate measurements are reported for the first and the second 2+
states in N=Z 64Ge. The experimental results are in excellent agreement with
large-scale Shell Model calculations applying the recently developed GXPF1A
interactions. Theoretical analysis suggests that 64Ge is a collective
gamma-soft anharmonic vibrator. The measurement was done using the Recoil
Distance Method (RDM) and a unique combination of state-of-the-art instruments
at the National Superconducting Cyclotron Laboratory (NSCL). States of interest
were populated via an intermediate-energy single-neutron knock-out reaction.
RDM studies of knock-out and fragmentation reaction products hold the promise
of reaching far from stability and providing lifetime information for excited
states in a wide range of nuclei
Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy
The Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet were used to measure
the free neutrons and heavy charged particles from the radioactive ion beam
induced 32Mg + 9Be reaction. The fragmentation reaction was simulated with the
Constrained Molecular Dynamics model(CoMD), which demonstrated that the
of the heavy fragments and free neutron multiplicities were observables
sensitive to the density dependence of the symmetry energy at sub-saturation
densities. Through comparison of these simulations with the experimental data
constraints on the density dependence of the symmetry energy were extracted.
The advantage of radioactive ion beams as a probe of the symmetry energy is
demonstrated through examination of CoMD calculations for stable and
radioactive beam induced reactions
Magnetic Moment of the Fragmentation Aligned 61Fe(9/2)+ Isomer
We report on the g factor measurement of the isomer in (). The isomer was produced and spin-aligned via a projectile-fragmentation
reaction at intermediate energy, the Time Dependent Perturbed Angular
Distribution (TDPAD) method being used for the measurement of the g factor. For
the first time, due to significant improvements of the experimental technique,
an appreciable residual alignment of the isomer has been observed, allowing a
precise determination of its g factor: . Comparison of the
experimental g factor with shell-model and mean field calculations confirms the
spin and parity assignments and suggests the onset of deformation due
to the intrusion of Nilsson orbitals emerging from the .Comment: 4 figures. Submitted to Phys. Rev. Let
Computational Study of the Photochemical Fragmentation of Hydantoin
The mechanism of the photochemical fragmentation reaction is investigated theoretically using the model system, hydantoin, using the CAS(22,16)/6-31G(d) and MP2-CAS-(22,16)/6-311G(d)//CAS(22,16)/6-31G(d) methods. The model investigation demonstrates that the preferred reaction route for the photofragmentation reaction is as follows: hydantoin → Franck-Condon region → conical intersection → fragment photoproducts (i.e., CO, isocyanic acid, and methylenimine). The theoretical finding additionally suggests that no organic radicals exist during the fragmentation reaction. Moreover, due to the high activation energy, the theoretical evidences suggest that it would be difficult to yield the three fragments under the thermal reaction. All the above theoretical observations are consistent with the available experimental results
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