Orbit Distortion Research Articles

ChemInform Abstract: Secondary Orbital Interaction vs. Orbital Distortion in Stereoselectivity.

AbstractFrontier orbital theory is applied on reactions such as electrophilic additions to norbornene and reductions of 2‐methylcyclohexanone and 2,7‐dimethylbenzocycloheptenone.

Secondary orbital interaction vs. orbital distortion in stereoselectivity

Stereoselectivities in reactions such as electrophilic additions to norbornene and 1-methoxycyclohexene-2, and reductions of cyclohexanone derivatives and a benzocycloheptenone one have been interpreted using frontier orbital theory. We concluded that the secondary orbital interaction is more important for the selectivities than the orbital distortion at the reaction center. This conclusion may be a motive for reexaminations of factors in stereoselectivities which could not be interpreted by the orbital distortion at the reaction center.

Direct measurement of ion phase-space orbits in an electrostatic field.

Ion orbits are followed in phase space by means of a new scheme of the optical tagging plasma diagnostic technique. An orbit distortion for ions interacting resonantly with an ion acoustic wave is clearly observed even in the low excitation regime, where the plasma response and the corresponding macroscopic fields exhibit linear behavior.

Orbit distortion due to UVSOR wiggler

A three-pole wiggler with a maximum magnetic field of 4 T was installed in the UVSOR electron storage ring. The insertion effect on the tune and the closed orbit of the stored beam is not negligible. The measured tune shifts are in good agreement with the values estimated from results of the magnetic field measurement. Compensation of the vertical closed orbit distortion due to misalignment of coils of the wiggler was tried with a vertical steering magnet. However, compensation is not perfect at the maximum excitation level because the distance between the steering magnet and the wiggler is not sufficiently short.

Spin–orbit distortion of the hyperfine structure in heavier molecules: Breakdown of the case (aβ) formalism in the B 3Φ–X 3Δ system of gaseous NbN

A detailed analysis of the rotational and hyperfine structure of the (0,0) band of the B 3Φ–X 3Δ electronic transition of NbN has been performed from sub-Doppler spectra taken with linewidths of about 50 MHz. The Nb hyperfine structure is impressively wide in both states, but particularly so in X 3Δ where one of the unpaired electrons occupies a σ orbital derived from the metal 5s orbital. The electron spin and hyperfine structures do not follow the expected case (aβ ) coupling because of extensive second order spin-orbit effects. It is shown that the asymmetry in the spin–orbit structure of X 3Δ is explained almost quantitatively by interaction with a 1 Δ state from the same electron configuration (which lies at 5197 cm−1); also cross terms between the spin–orbit and Fermi contact interactions in the matrix element 〈3Δ2‖H‖1Δ〉 produce a large correction to the apparent coefficient of the I⋅L magnetic hyperfine interaction in X 3Δ2. The hyperfine structure in a triplet state turns out to be extremely sensitive to the details of the electron spin coupling, and reversals in the sense of the hyperfine structure in the 3Φ4–3Δ3 and 3Φ2–3Δ1 subbands are shown to be consistent with the3Δ state being a regular spin–orbit multiplet (A>0). Particular care has been taken with the calibration, which has meant that extra terms have needed to be added to the magnetic hyperfine Hamiltonian to account for the spin–orbit distortions: instead of the usual three parameters needed in case (aβ ) coupling, the B 3Φ state has required four parameters and the X 3Δ state has required five. The model explains the data very well, and the standard deviation in the least-squares fit to more than 1000 hyperfine line frequencies was 0.000 58 cm−1 (17 MHz).

Low emittance and positron storage operation at the Photon Factory (invited)

The Photon Factory ring has been successfully in operation with a lower horizontal emittance of 127-nm rad since February 1987. It was previously 404-nm rad. There have been many kinds of beam instabilities and the closed orbit distortions observed. These causes have been studied diagnostically in order to find a solution. Positron storage has also been achieved as the next step. In positron storage, the two-stream instability caused by ion trapping has completely disappeared and the abrupt decrease of the beam lifetime presumably due to dust trapping has not been observed since.

ChemInform Abstract: Optical Activities of Saturated Ketones: Nonplanarities of Carbonyl Chromophores and Chiral Perturbational Effects of Substituents

Abstract The optical activities of a series of saturated ketones having the bicyclo [2,2,1] heptan-2-one skeleton were investigated by the rotatory strength calculation using the semiempirical MNDOC-SCF-MO method. It was found from geometrical optimization based on the energy gradient method that the out-of-plane bending of the carbonyl chromophores is an important factor in determining the optical activities of saturated ketones, and further that the chiral perturbational effects of substituents are closely correlated with the out-of-plane bending of the carbonyl chromophores through the distortion of the carbonyl orbitals.

Optical activities of saturated ketones: Nonplanarities of carbonyl chromophores and chiral perturbational effects of substituents

The optical activities of a series of saturated ketones having the bicyclo [2,2,1] heptan-2-one skeleton were investigated by the rotatory strength calculation using the semiempirical MNDOC-SCF-MO method. It was found from geometrical optimization based on the energy gradient method that the out-of-plane bending of the carbonyl chromophores is an important factor in determining the optical activities of saturated ketones, and further that the chiral perturbational effects of substituents are closely correlated with the out-of-plane bending of the carbonyl chromophores through the distortion of the carbonyl orbitals.

Steering Magnet Power Supply Control System for the TRISTAN AR

The closed orbit distortion of TRISTAN Accumulation Ring (AR) is corrected by the steering magnets1-2 (correction dipole magnets). These magnets are excited by the bipolar power supplies with the rated power of about 1 KVA. The power supplies are controlled remotely through the serial camac dataway3. The camac modules which include the microprocessor are developed for this system and these modules send out the reference current patterns to the individual power supply.

Undulator and Wiggler of UVSOR

A 600 MeV electron storage ring whose nickname is UVSOR (Ultra Violet Synchrotron Orbital Radiation) was constructed at Institute for Molecular Science to be a synchrotron radiation source for the research of molecular science and its related fields. New light sources, a permanent magnet undulator and a wiggler were installed in the ring. The undulator has 35 periods and its maximum magnetic field is 0.3 T . The maximum magnetic field of the wiggler is 4 T. Electron beam could be injected and stored in the ring when these devices were excited with the maximum magnetic fields, individually. Results of the measurement of the magnetic field distributions of them, and tune shifts and closed orbit distortions due to them are presented.

Nu Shifts in Betatron Oscillations from Uniform Perturbations in the Presence of Non-Linear Magnetic Guide Fields

Uniform magnetic field perturbations cause a closed orbit distortion in a circular accelerator. If the magnetic guide field is non-linear these perturbations can also cause a Nu shift in the betatron oscillations. Such a shift in radial Nu values has been observed in the Bevalac while studying the low energy resonant extraction system. In the Bevalac, the radial perturbation comes from the quadrants being magnetically about 0.8% longer than 900. The normal effect of this type of perturbation is a radial closed orbit shift and orbit distortion. The nu shift, associated with this type of perturbation in the presence of a non-linear guide field, is discussed in this paper. A method of handling the non-linear n values is discussed as well as the mechanism for the associated Nu shift. Computer calculations are compared to measurements.

Study of Random and Systematic Multipoles in the SSC Lattice

The expression for the tune shift and an orbit distortion is derived by the first order canonical transformation. The program based on these formulas is described and used for numerical camparison of the non-linear effects in the SSC lattices. The results are compared with analytic estimations. The choice of the main parameters of the SSC lattices is discussed.

Statistics of Dipole Steering in the Tevatron

Methods of calculating the expected rms orbit distortion and the expected peak orbit distortion for a large FODO synchrotron are described. An expression for the expected rms correction element dipole strength necessary to correct the closed orbit of a large FODO synchrotron is derived. The uncorrected closed orbit of the FNAL Tevatron accelerator is determined from beam position data and operational settings of the correction element dipole magnets. The uncorrected orbit and correction element dipole strengths are compared to the results of the Tevatron design study. Use of these expressions for SSC lattices is discussed.

Operational Results of Optics Handling and Closed Orbit Correction in the Tristan Accumulation Ring

The optics handling system of the TRISTAN accumulation ring (AR) is facilitated by the general purpose computer of KEK as well as the machine control computers and has been dealing with many kinds of optics successfully since November 1983. Also a series of correction procedures has reduced r.m.s. values of closed orbit distortion(c.o.d.) at position monitors from 8.5mm to 0.6mm horizontally, and from 2.3mm to 0.3mm vertically in the typical optics of AR. Using the estimated errors, the pre-correction facility has been installed in AR to make an orbit correction possible in a completely new optics before beam injection.

The effect of beam-cavity interaction on the closed orbit and the beam shape

Analytic formulas for the closed orbit distortion (COD) and the beam shape distortion (BSD) due to the beam-cavity interaction are obtained with the cumulative, i.e., the multi-turn effect taken into account. The formulas are extended so that they are applicable to storage rings with many cavities and several counter-rotating bunches. In particular, the COD and the BSD of the bunches at the collision point are estimated for the case of TRISTAN. The effect of the COD and the BSD on the luminosity is found to be small. The beam-cavity interaction causes a difference between the closed orbits of the electron bunches and the positron bunches of almost 10% of the closed orbit due to magnet imperfections.

The light curve of a variable star subject to orbital tidal distortion

The light curve of a variable star subject to orbital tidal distortion

New Method for Inverting the Closed Orbit Distortion Problem

A certain class of magnet misalignments in storage rings and other accelerators produces closed orbit distortions (CODs). Quite often the CODs are measured at a fewer number of locations (N) than the number of misalignment parameters (M). There is a linear relation between COD measurements, u(j), j= l, ..., N and the misalignment parameters e(k), k= l, ..., M. Hence the c(k)' s are underdetermined. If M < 2N, one can obtain an overdetermined set of equations by measuring the COD at two quadrupole settings. There are several ways of inverting the COD measurements to get the misalignment parameters that are fairly insensitive to errors in the measured CODs. A computer program called CODINV has been written to test some of these schemes. Two schemes give fairly good results when applied to the lattice of the Los Alamos Proton Storage Ring (PSR). The first scheme requires measurements at two nearby tunes and the use of singularvalue decomposition methods. The second scheme requires measurements of the CODs in the FODO and DOFO cell arrangements but is easier mathematically.

Polarization Measurements at PETRA

Recent measurements of beam polarization in the electron-positron storage ring PETRA are presented. A method is described for compensating the depolarizing effects caused by vertical closed orbit distortions. This technique has been successfully applied, and reproducible polarization up to 80 % has been obtained both in single beam and colliding beam operation with luminosities of about 3 · 1030 cm-2S-1· Polarization measurements as a diagnostic tool for studying other beam parameters such as absolute energy and momentum compaction factor are also briefly described. These latter measurements have been performed with the help of a fast depolarizing device.

Nonexistence of a positron-hydrogen-atom bound state

The problem of the existence of bound states for the e+-H system was investigated by A~o~soN, KLEIN~AN and SrRucI~ (1), by AR~ou~ and SCRAD~R (~) and by ARMOUR (2). These papers conclude that the fundamental state of the hydrogen atom does not support a bound state with a positron. A lower bound to the so-called critical mass of the positron is given. Although the last results are believed to be very accurate, the matter can be still considered to be settling down. For this reason, a further proof of the nonexistence of a positron-hydrogen bound state is still of interest. In this paper we confirm the nonexistence of such a bound state through the use of a simple approximate model and a direct calculation method. Both the model and the related calculation will be used in subsequent work to study the existence of positron-atom resonances. The calculation method consists in the determination of the e+-H potential with an adiabatic, close-coupling approximation. In this approximation the positron is considered to approach the atom so slowly that the atom can be considered to be fully distorted for each position of the positron. The energy levels eventually supported by the potential well are determined. The calculation scheme closely follows the one used by STON~ (4). The potential is buil t as an expansion in which the static (repulsive) term is dominant. The polarization potential is introduced as the finite sum of the terms representing the atomic distortion of several excited orbitals. The practical l imitations of the close-coupling technique are well known (4). As a matter of fact a correct expan-

Electronic Structure of Oxide Surfaces

Electronic structures of oxide surfaces are discussed based on the results of recent DV (Discrete-Variational) -Xα cluster calculations. Surface electronic structures of oxide crystals with mixed ionic and covalent attributes are achieved by the following : A) reduction of the Madelung potential compared to the bulk, B) strong field on the surface ionic site and the distortion of the ionic orbitals, C) the lack of orbital mixing between the surface ions and its nearest removed counter ions, and D) the reduction of the ionicity of surface ions and the enhanced covalency on the remaining bonds around it.The localized electronic states associated with surface defects are clarified and their significance to surface chemical activity is discussed. The origin of the compensating charge of the polar surfaces is made clear and their peculiar electronic properties are studied.