On Metal-Atom Clusters IV. Photoionization thresholds and multiphoton ionization spectra of alkali-metal molecules

The investigation of electronic and structural parameters of metal molecules as a function of size may be decisive for understanding and control of heterogeneous catalysis with finely divided metals. Metal-atom clusters can be prepared by several methods, most of which yield a molecular mixture only. Expansion of an atomic vapour into vacuum through a supersonic nozzle creates a complex cluster-spectrum which has been investigated by photoionization using a mass-spectrometer as selective detector. Broad band single photoionization ( PI. ) yields the abundances and ionization thresholds for Na_x(x?16), K_x(x?12) and Na_xK_y(x+y?6). Rough indications about other deactivation channels of excited alkali-molecules are obtained from an analysis of the photoionization efficiency (PIE.) curves. Two-photon PIE. curves with narrow-band (laser) light sources give an accurate photoionization threshold value and detailed information on ionization processes. Two-photon ionization spectra via a real intermediate state reached by laser excitation are equivalent to normal absorption spectra, if the exciteation step is controlled by the true transition probabilities. By investigation of the power dependence of the ion current of Na as a function of the wavelength of the tunable cw dye laser (excitation) and of the ionizing Ar⁺- or Kr⁺-laser, conditions under which true spectra are obtained have been clarified, in good agreement with a photon-kinetic model of the processes involved. Vibronic and rovibronic spectra of several transitions in Na₂ and K₂ have been measured. Similarly a spectrum of Na₃ has been determined mass-selectively. The scope of the new method for an absorption spectroscopy in molecular beams is discussed.     

The radiation gauge static potential for non-abelian gauge fields

The static potential between a fermion and an anti-fermion in a group singlet state is calculated, through two loops, in the radiation gauge first order formalism. The results of this calculation imply that the Coulomb propagator is not sufficient to determine the static potential: a new function of the coupling constant α_s(?t) is also required.     

Anomalous resistivity of iodine-free 2H-NbSe2

Resistance ratios of crystals of 2H-NbSe₂ grown with and without iodine were measured over the temperature range 6K–40K. Iodine-free crystals had higher ratios than any NbSe₂ previously reported and exhibited an abrupt anomaly at the onset of the charge density wave phase. All crystals displayed a cubic temperature dependence of their resistivities below 18K.     

Application of a new three-dimensional k·p model for the A-15 crystals to the properties of V3 Si

The new three-dimensional k·p model for the electronic structure of A-15 compounds gives satisfactory results for the magnetic susceptibility; shear modulus; tetragonal strain at the transition temperature T_m; and the magnetic field effect on T_m and shear mode sound velocity.     

Laser Stark measurements on OCS including the observation of zero-field-forbidden ΔJ = 0, ±2 transitions

Laser Stark measurements have been made on the 02⁰000⁰0 and 03¹001¹0 vibrational transitions of ¹⁶O¹²C³²S, ¹⁶O¹²C³⁴S, and ¹⁸O¹²C³²S, and on the 03¹001¹0 transition of ¹⁶O¹³C³²S, using a CO₂ laser. In addition to providing dipole moment information for excited vibrational states, these measurements give vibrational band centers accurate to several megahertz. To aid in optical pumping experiments, several near coincidences between CO₂ laser transitions and OCS absorption lines are discussed. Electric-field-allowed ΔJ = 0 transitions are observed for the 2ν₂ band of ¹⁶O¹²C³²S and ¹⁶O¹²C³⁴S, as well as ΔJ = 2 transitions for the same band of ¹⁸O¹²C³²S.     

Ellipsometric analyses for an absorbing surface film on an absorbing substrate with or without an intermediate surface layer

Various ellipsometric analyses have been derived to characterize the optical properties of a single-layer or a double-layer surface film overlaid on a substrate material. The general numerical technique is independent of the method (or methods) used in the series of ellipsometric measurements which provide the raw data. The convergence to unambiguously determined values of the unknown parameters is systematically carried out in the numerical search procedure. Selected examples are presented to illustrate the validity of various analyses and the possible usage of these analyses to optimize the experimental conditions and measurement methods.     

PMMA stereocomplex: Study of the aggregation process by electron microscopy

The structure of stereocomplex aggregates formed from isotactic and syndiotactic poly (methyl methacrylate)s was studied in tetrahydrofuran (THF) by transmission electron microscopy (TEM). We have found that the primary stereocomplex particles are nearly spherical and, as the complexation advances, the particles lengthen. Eventually aggregates branch to form a three-dimensional network.     

Goals and Constraints in Decision-making<Superscript>†</Superscript>

Most problems in management involve multiple goals and two approaches to solving managerial problems have been suggested: optimizing and satisficing. The first covers methods of trade-offs, optimizing in tandem, conversion of goals into constraints and goal programming. The second mainly centres on norm setting and on interval programming. It is argued that cost-benefit analysis essentially belongs to the first group and that, contrary to some suggestions, the differences between the industrial and public sectors (as far as O.R. is concerned) are not related to differences between the optimizing and satisficing philosophies.