Orbital Confinement Research Articles

Molecular orbital confinement effect of mesoporous silica of MCM-41 on conjugated polymer

A set of conjugated polymers with different molecular diameters was incorporated into channels of mesoporous silica of MCM-41. Study on UV-Vis and photoluminescent (PL) spectra of these composites revealed regular variation of band gap of frontier orbital along with the variation of diameter of the polymers by comparison with UV-Vis and PL spectra of the polymers in CHCl 3 solution. The results showed evidence in support of the molecular orbital confinement effect in the composite of the conjugated polymer/mesoporous silica.

Observation of azo chromophore fluorescence and phosphorescence emissions from DBH by applying exclusively the orbital confinement effect in siliceous zeolites devoid of charge-balancing cations.

The molecular orbital (MO) confinement theory predicts that the HOMO and LUMO of an organic guest may become distorted when the dimensions of the host cavity approach closely those of the MO (Corma, A.; García, H.; Sastre, G.; Viruela, P. M. J. Phys. Chem. B 1997, 101, 4575-4582). Generally, quantum chemical calculations assume that the MO extends over all the space. However, the fact that a molecule is confined within a restricted cavity might impose certain limits to its MO. In agreement with this theory, we have observed for the first time the phosphorescence emission from 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) upon incorporation in zeolites devoid of charge-balancing cations, even at room temperature. This observation may be rationalized on the basis of two possible effects: (i) Decrease of the HOMO-LUMO gap induced by confinement of the azo np* chromophore favors ISC, and (ii) inhibition of radiationless deactivation pathway by the immobilization of DBH within the zeolite host favors long lifetimes.

Molecular orbital confinement of a Schiff base molecule in the nanoporous channels of MCM-41 host

A new Shiff base molecule N, N ′-bis(2-hydroxy-5-methylbenzylidene)-1,2-ethanediamine ( 1) has been successfully encapsulated in the nanoporous channels of MCM-41 host. The bathochromic shifts of the 0–0 transitions have been correlated with the reduction of the HOMO–LUMO band gap accompanying by the increased energies of the frontier orbitals. This trend indicates that the molecular orbital confinement of organic molecules is indeed realized in larger cavities, such as nanoporous MCM-41. The variations in the 0–0 transitions observed here have also been confirmed by theoretical calculations.

Spectroscopic Evidence in Support of the Molecular Orbital Confinement Concept: Case of Anthracene Incorporated in Zeolites

Spectroscopic Evidence in Support of the Molecular Orbital Confinement Concept: Case of Anthracene Incorporated in Zeolites

Environmental effects on molecular response in materials for non-linear optics

The concept of a molecule in a material is discussed. The properties of such entities differ from those of the free molecules. These differences are explored with particular reference to non-linear optical response. Molecular distortion induces changes exemplified by a non-zero static first hyperpolarizability β for the S8 molecules in the crystalline complex CHI3·3S8, which dominates the net response. Strong permanent electric fields modify the response, but for urea can be calculated accurately enough to reproduce the refractive indices and quadratic susceptibility reasonably accurately. Non-uniform fields also have significant effects especially in combination with non-uniform response, as shown by calculations on model Langmuir–Blodgett films and on surface-induced second-harmonic generation (SHG). Orbital confinement tends to suppress response but may be less important in large molecules. In general, good quantitative theories of these factors are now available.

On a temporary confinement of chaotic orbits of four dimensional symplectic mapping: A test on the validity of the synthetic approach

Poincare maps for Hamiltonian systems with 3 degrees of freedom lead to the study of four dimensional symplectic mappings. As a test for the validity of a synthetic mapping of order 3 using gradient informations, we study the evolution with time of Liapounov Indicators in the case of the four dimensional standard map with chaotic and stable zones. Both Liapounov Indicators show the same behaviour for the real and synthetic mappings. They reveal exploding diffusion phenomena for temporarily confined chaotic orbits. The distribution of the time of explosion fits well with a Poisson law for the real mapping, but not for the synthetic one. However the mean time of explosion is essentially the same in both cases.

Equilibrium, Stability, and Deeply Trapped Energetic Particle Confinement Calculations for l = 2 Torsatron/Heliotron Configurations

This paper studies confinement properties of 1 = 2 torsatron/heliotron configurations with number of toroidal field periods, M, in the range of 10 to 14. This involves the calculation of zero-current and flux-conserving equilibria; stability against Mercier modes and low-n ideal modes, with n denoting the toroidal mode number; and orbit confinement of deeply trapped energetic particles. Optimization of both magnetohydrodynamic (MHD) and transport properties is pursued under the condition of plasma aspect ratio A = R/a {ge} 7, with R denoting the major radius and a the average plasma radius. For configurations with M, {le} 12, an average MHD beta limit of 4 to 5% is possible. The addition of a quadrupole field improves the confinement of trapped particles at zero pressure, but particle losses increase with increasing beta. This loss is less severe if the vacuum magnetic axis is shifted slightly inward. A configuration with M = 10, a coil pitch parameter p{sub c} in the range 1.25 to 1.30, and an added quadrupole field satisfies the beta and energetic particle confinement requirements for the next generation of large torsatron/heliotron devices.

Alpha-Particle Losses in Compact Torsatron Reactors

Loss of alpha particles in compact torsatron reactors is studied. For 6, 9, and 12 field period reactors, the direct loss is a relatively weak function of radius and energy and varies from approx. =33% for M = 6 to approx. =18% for M = 12. Loss of alpha particles through scattering into the loss region is calculated using the Fokker-Plank equation for fast ions and found to contribute an additional alpha-particle energy loss of approx. =15%. The consequences of these relatively large losses for torsatron reactor design are discussed. The relationship between the direct particle losses and the magnetic field structure is also studied. Orbit losses from a variety of stellarator configurations are calculated and a figure-of-merit that characterizes the orbit confinement of a magnetic configuration is deduced from these calculations. This figure-of-merit is used to show how the direct losses might be reduced at low aspect-ratio. Effects of finite beta on the direct particle losses are also addressed, and are shown to significantly increase the direct losses in some configurations. 15 refs., 8 figs.

Stability of motions near resonances in quasi-integrable Hamiltonian systems

Nekhoroshev's theorem on the stability of motions in quasi-integrable Hamiltonian systems is revisited. At variance with the proofs already available in the literature, we explicitly consider the case of weakly perturbed harmonic oscillators; furthermore we prove the confinement of orbits in resonant regions, in the general case of nonisochronous systems, by using the elementary idea of energy conservation instead of more complicated mechanisms. An application of Nekhoroshev's theorem to the study of perturbed motions inside resonances is also provided.

Neutral Beam Injection for the Doublet III Device

Neutral beam injection into Doublet III has been considered with regard to the calculation of non thermalizing particle orbits and the confinement of such orbits. Injected particle loss, based upon these orbits, toroidal gyro-radius effects, and plasma transparency, is calculated to be on the order of 5 percent for coinjection. Near-perpendicular injection at 80 keV has been chosen with the resulting available injection window of 1014 cm-3 ⩽ n(0) ⩽ 3 × 1014 cm-3. Injection into plasmas with n(0) ⩽ 1014 cm-3 will yield large losses due to the increasing transparency of the plasma, whereas injection into plasmas with n(0) ⩾ 3 × 1014 cm-3 shifts the deposition profile toward the plasma edge.