Table of contents

A CO₂ TEA laser was used for optical pumping of ¹⁴NH₃. Thirteen CO₂ lines, which deviate by 0.05 cm^-1 or less from transitions in ¹⁴NH₃, were effective in producing submillimeter laser transitions. Most of the 24 emitted lines have wavelengths between 70 and 400 μm and represent rotation-inversion transitions in the ν₂ state of NH₃. A few short wavelength lines (30-70 μm) are 2ν₂ transitions obtained by pumping from the ν₂ state.

The influence of pressure, resonator length and outcoupling on the appearance of the submillimeter lines was investigated. The choice of parameters was not critical for observing the lines, which in general had high gain. Each pump pulse delivered 1-50 mJ in 150 ns to the NH₃ gas. Some submillimeter lines persisted up to an NH₃ pressure of 30-70 torr or to 300-400 torr in a mixture of NH₃ and He.

The technique of longitudinal phase space analysis has been used to investigate the possible single and double dissociation in the reaction pp → pp π⁺π^-π⁰ at 19 GeV/c. The hypothesis of factorization has been tested and found to be in agreement with the data for the single dissociation process.

The peak-to-valley ratio in the bremsstrahlung induced fission of ²³⁸U has been measured at E_max = 800 MeV. The value obtained, 1.95±0.15, is in good agreement with earlier measurements at this laboratory. Current data on the peak-to-valley ratios at different maximum photon energies are presented and the discrepancies existing above 100 MeV discussed.

The ⁴¹K(α,nγ)⁴⁴Sc reaction has been studied at 10, 12 and 14 MeV incident energy. By use of single spectra, γγ-coincidence measurements and yield functions, the decay modes of several excited states have been obtained and spins have been assigned. On theoretical grounds a K = 0^- band has been proposed in ⁴⁴Sc. In the present work the following members of this band are suggested: 68 keV (1^-), 235 keV (2^-), 425 keV (3^-), 532 keV (3^-), 631 keV (4^-). Two possible candidates for the 5^- state are discussed.

A theoretical investigation of the 2p⁴(s+d) configurations in F I and Ne II is reported. The configurations have been interpreted by fitting the theoretical energy expressions to the observed energy levels using least-squares techniques. All parameter values are compared to the results of Hartree-Fock calculations. In the fitting procedure some parameters, notably all those representing configuration interaction, have been fixed at values equal to or slightly modified from the Hartree-Fock values. Eigenvalues and eigenvector compositions are given.

The influence of configuration interaction is most pronounced for 2s²2p⁴(¹D)3d²S_1/2 and is caused by interaction with 2s2p⁶²S_1/2 and 2s²2p⁴(¹S)3s²S_1/2. With this one exception the p⁴s ↔ p⁴d interaction is small for F I, but for Ne II considerable perturbations are found. The introduction of configuration interaction in the calculations for Ne II improves the description of the s configurations substantially whereas the improvement is less pronounced for the d configurations. The effect of introducing term-dependent Slater parameters has been studied in the 3d configuration in Ne II. It is found empirically that introduction of configuration interaction together with a correction of the (³P)3d⁴D term gives a marked improvement of the fit.

A tandem accelerator has been used for beam-foil excitation of chlorine and oxygen with beam energies from 6 MeV up to 42 MeV. Hydrogen-like transitions in ClVI to ClXIV and OVI to OVIII have been observed in the wavelength region 2 000-5 700 Å. The variation in the intensity of the lines with the beam energy has been used to determine the ionization stage of the ions producing the lines.

By using a model-independent statistical method, term values were determined for the rotational and vibrational levels of the X²Π, A²Δ, B²Σ^-, and C²Σ⁺ electronic states of CH, and the X¹Σ⁺ and A¹Π states of CH⁺. Molecular parameters were obtained from a least squares fit to these term values. A method based on exact numerical diagonalization of the respective perturbation matrices yielded parameters for the X²Π and B²Σ^- states of CH and the A¹Π and X¹Σ⁺ states of CH⁺, while the A²Δ and C²Σ⁺ states of CH had to be treated according to a polynomial model. In the case of CH several arguments indicate that the Λ-doubling of the X²Π ground state arises from interaction with the B²Σ^- state. A discussion of the influence of the predissociation observed for the B²Σ^- state on the X²Π Λ-doubling is also included. For CH⁺ good agreement was found between observed and pure precession values of the X¹Σ⁺ - A¹Π interaction matrix element.