Nils Elander

Microwave-enhanced radiochemistry

The application of microwaves to synthetic organic chemistry is currently experiencing considerable growth. Here we show how the area of radiochemistry, with particular reference to the synthesis of 3H- (or T-), 11C- and 18F-labelled compounds, can benefit. Faster, cleaner, more selective reactions are possible with the formation of much reduced levels of radioactive waste.

Spectroscopic constants and radiative lifetimes for valence‐excited bound states in SiO

Using the self‐consistent polarization propagator approximation we have calculated the spectroscopic constants for the following bound states in silicon monoxide: a 3Σ+, b3Π, d3Δ, e 3Σ‐, C 1Σ+, D 1Δ, A 1Π, E 1Σ+, 3Σ+(II), 3Σ+(III), 3Π (III), F 1Σ+, H 1Σ+, and G 1Π. The molecular parameters for the seven lowest states agree very well with experiments, whereas the seven remaining levels were determined less accurately. The electronic transition moments were calculated for the dipole allowed transitions. The calculated radiative lifetime for the A 1Π state was found to be 49.5 nsec. With the experimental potential energy curves the corresponding lifetime was 31.6 nsec.

A finite element implementation of exterior complex scaling for the accurate determination of resonance energies

An implementation of exterior complex scaling using the finite elements method with high degree polynomials is presented. We apply the method to find the resonances of the potential 7.5r 2e−r and of a phenomenological coupled channel model of the CaH molecule. In both cases the method is quickly convergent and extremely stable numerically. Convergence could be pushed to the point where the real parts of most resonance energies were independent of the complex scaling angle and of the exterior scaling radius within machine precision (14 significant digits). All imaginary parts were stable to at least eight significant digits. Several resonances of CaH which had evaded searches with a finite difference method could be located.

The spectrum of SiO in the vacuum ultraviolet region

Abstract The absorption spectrum of SiO has been photographed at high resolution in the region 1200–1500 A. Several new electronic states have been observed, valence states as well as Rydberg states. Tables of the molecular constants of all the known states of SiO are given. Due to interactions between the electronic states, the constants of all states analyzed vary irregularly. From the Rydberg series a value of the ionization potential has been derived. It agrees with the value earlier reported, 11.6 ± 0.2 eV.

Titchmarsh–Weyl theory and its relations to scattering theory: Spectral densities and cross sections; Theory and applications

The radial equation (or set of equations) derived in scattering theory is analyzed by means of Titchmarsh–Weyl theory for singular second‐order differential equations. In particular we have focused on the spectral density concept and the corresponding relation to the scattering cross section. The method of complex deformations is brought in as a necessary ingredient in the evaluation of the underlying pole strings, which together with the background build up the actual dispersion relation data. The analysis is supported by numerical applications to a centrifugal family of simple potentials.

Lifetimes of Excited Levels in Some Important Ion-molecules Part I: NH+, OH+ and SH+

The spectra of NH+, OH+ and SH+ in the range 3 000-5 000 A have been studied at 0.2-0.4 A FWHM resolution using the High-Frequency Deflection technique. Radiative lifetimes of low-lying excited electronic states in these molecules were simultaneously measured and found to be of the magnitude of 400-1 100 ns.

Fast chemistry in microwave fields: Nucleophilic 18F-radiofluorinations of aromatic molecules

Abstract Nucleophilic aromatic radiofluorinations with [18F]fluoride in a microwave field were investigated in activated, partially deactivated and deactivated aromatic compounds. A coaxial resonance microwave cavity was used to produce a well-defined electromagnetic field in the samples. The leaving group on the aromatic rings as well as the ortho, meta and para orientation of electron-withdrawing and electron-donating substituents were varied. Yields comparable to or better than those reported for thermal treatments were obtained in very short reaction times (≤0.5 min, i.e. 1 20th – 1 40th the thermal times) with very low microwave intensity and followed the trend of reactivity expected from the substrates activation for nucleophilic substitution.

Microwave cavities: Some parameters affecting their use in radiolabelling reactions

Abstract The experimental conditions influencing the strength of the electromagnetic field delivered to the sample by a coaxial microwave resonance cavity were investigated. Radiofluorinations using this equipment indicate that this technique is useful for shortening reaction times and affecting the product distribution in radiolabelling reactions.

Solving the Coulomb scattering problem using the complex-scaling method

We present a rigorous formalism for solving the scattering problem for long-range interactions without using exact asymptotic boundary conditions. The long-range interaction may contain both Coulomb and short-range potentials. The exterior complex-scaling method, applied to a specially constructed inhomogeneous Schrodinger equation, transforms the scattering problem into a boundary problem with zero boundary conditions. The local and integral representations for the scattering amplitudes have been derived. The formalism is illustrated with numerical examples.

UV monitoring of microwave-heated reactions--a feasibility study.

UV/Visible spectroscopy has been used to monitor the progress of the formation of benzimidazole from the reaction between 1,2-diaminobenzene and formic acid. The reaction was performed at three concentration levels, each becoming more dilute so that at the most dilute level direct UV monitoring from the reaction sample was possible. At each level the reaction was conducted by conventional and by microwave heating. The success of the microwave reaction at the most dilute levels encourages the construction of a microwave reactor/UV/Vis spectrometer hybrid instrument for the monitoring of this and other reactions.