Published in Appl. Opt. 54 B177-B184 in 2015
G.P. Können
The radiance distribution of light scattered by randomly oriented ice crystals differs fundamentally from the radiance distribution of light scattered by spherical raindrops or by preferentially oriented ice crystals. A formalism for light scattering by randomly oriented crystals is given and applied to four examples, among them the circular 22° halo and the antisolar halospot, the latter being the glory analogue for ice crystals. A long-standing misconception about the nature of the radiance distribution of circular halos is quantified and discussed.
Published in Nederlands Tijdschrift voor Natuurkunde 80, 253 (Translated from Dutch) in 2014
G.P. Können
A ‘broken rainbow’ teaches us that seawater is salt – in the same way that the Venus rainbow once taught us that the cloud drops on Venus are sour.
Published in Geophys. Res. Lett. 35, L23702, doi:10.1029/2008GL035967 in 2008
H.W. van den Brink and G.P. Können
A general expression for the statistical distribution of the probability of the highest event occurring in a record is presented. This result can be empirically applied to situations where records are available for multiple geographical locations. The empirical estimation of the probability of the highest events provides a means to assess whether the assumed (extreme value) distribution is appropriate for extrapolation or not. The approach allows for combining the highest events from different records and to validate estimated return periods in the order of the length of the combined records. The method is illustrated with an analysis of the annual extreme wind speeds over the North Atlantic area according to the ERA40 dataset, showing that the Gumbel distribution is in favor of the GEV distribution to describe the (appropriately transformed) extreme wind speeds up to return periods of 104 years.
Published in Appl. Opt. 42, 379-389, doi:10.1364/AO.42.000379 in 2003
Siebren Y. van der Werf, Günther P. Können, Waldemar H. Lehn, Frits Steenhuisen, and Wayne P.S. Davidson
Ray-tracing analyses show that the NZ effect distorted the relative positions of Jupiter and the Moon in such a way that the looked-for fingerprint of the 1597 conjunction occurred almost 2 h after the true conjunction. The quoted direction for the apparent Moon-Jupiter conjunction is then found to be accurate to within 1°. This delay of the apparent conjunction largely explains the error of 29° in their longitude determination. The truthfulness of the observations brackening the first recording of the NZ effect, debated for four centuries, now appears to be beyond doubt.
Published in J. Opt. Soc. Am. A 4, 601-608, doi:10.1364/JOSAA.4.000601 in 1987
G. P. Können
The polarization distribution in the sky during a total solar eclipse is calculated with a simple secondary light scattering model. The model can explain various observations during totality, including the measurements by Shaw of the polarization distribution of the sky in the solar vertical during the 1973 total eclipse.
Published in Q. J. Mechanics Appl. Math. 34, 311-325doi:10.1093/qjmam/34.3.311 in 1981
J. H. de Boer and G. P. Können
A differential-geometric approach is applied to study the approximation of the Airy integral by a Fresnel integral.
Published in Chem. Phys. Lett. 30, 11-16, doi:10.1016/0009-2614(75)85486-8 in 1975
G. P. Können, A. Haring, and A.E. de Vries
Cross sections for ion formation in C + O2 collisions have been measured as a function of kinetic energy up to 15 eV. Charge transfer gives rise to C+, O2-, C+, O2-, and free electrons. Five processes leading to these products has been identified. Reactive ionisation is taking place according to three processes: C + O2 -> CO+ + O + e-; CO+ + O-; CO + O+ + e-.
Published in Rad. Eff. 26, 23-29, doi:10.1080/00337577508237415 in 1975
G. P. Können, A. Tip and A.E. de Vries
Our previous model for dimer sputtering is extended to the formation of larger clusters. A simple analytical expression is obtained for the energy distribution of any cluster in the high energy limit. Comparison with experimental data on ionic tungsten clusters shows agreement. Indications are found that for the ionic crystal KI sputtering of non-adjacent K and I atoms from the lattice gives an important contribution to dimer formation.
Published in University of Amsterdam in 1974
G. P. Können
Experiments are described on negative surface ionization of eV halogens, on sputtering from alkalihalide surfaces, on ionization and fragmentation in eV halide-aniline collisions, and on reactive ionization in C-O2 collisions. A theoretical expression is obtained for the energy distribution of sputtered polyatomic particles.
Published in Rad. Eff. 21, 269-274, doi:10.1080/00337577408232416 in 1974
G. P. Können, A. Tip and A.E. de Vries
A theoretical expression is obtained for the energy distributions of sputtered dimers. The model assumes recombination of neighbouring atoms sputtered according their individual single particle energy distribution functions. A comparison with the experimental results for K2 and KI sputtered from polycrystalline K and KI surfaces, respectively, shows a good agreement.
Published in Rad. Eff. 21, 171-179, doi:10.1080/00337577408241459 in 1974
G. P. Können, J. Grosser, A. Haring, A. E. de Vries and J. Kistemaker
Velocity selected beams of atoms and molecules are produced by sputtering from alkalihalide surfaces under 6 keV Ar+ bombardment. Monoatomic as well as polyatomic particles are found, the latter's fraction decreasing with energy. Above a few eV the energy distribution of a given alkali or halogen atom is independent on the target from which it is sputtered. Some sputtered atoms and molecules seem to be formed in long lived exited states.
Published in Chem. Physics 6, 205-216, doi:10.1016/0301-0104(74)85061-5 in 1974
G. P, Können, J. Grosser, A. Haring, F. Eerkens, A. E. de Vries and J. Kistemaker
Ionisation and fragmentation of aniline, n-propylbenzene, CH4, C6H6, propane and cyclohexane is studied under halogen impact. The results show an analogy with photon impact. They are discussed in terms of potential curve crossing in the halogen-organic molecule system.
Published in Chem. Phys. Lett. 21, 445-447, doi:10.1016/0009-2614(73)80279-9 in 1973
G. P. Können, J. Grosser, A. Haring and A. E. de Vries
Negative surface ionisation of hyperthermal halogen atoms was studied as function of kinetic energy on thoriated tungsten and niobium wires. The transition from a thermal equilibrium process to direct reflection causes the ionisation to increase drastically above thermal energies: efficiencies up to 40% were found for 30 eV Cl atoms impinging on thoriated tungsten.
Published in Nederland Tijdschrift voor Natuurkunde 38, 265-271 and 283-287 in 1972
G. P. Können
The optical phenomena in the sky - coronas, rainbows, halos and glories - all have their analogue in particle scattering. Examples are shown of these phenomena in the angular pattern of atom-atom scattering experiments.
Published in University of Amsterdam and FOM Institute for Atomic and Molecular Physics, Amsterdam in 1970
G. P. Können
An apparatus is build that efficiently generate beams of halogen atoms in the eV range. Potential experiments about electron transfer in atom-molecule collisions are outlined.  The results of an experiment to explore the detection of thermal halogen atoms by means of negative surface ionization are presented.
Published in FOM Institute for Atomic and Molecular Physics, FOM Report 27323/AMOLF 68/338, Amsterdam in 1968
G. P. Können
A survey is given of positive and negative surface ionization. It includes tables, with handwritten updates, of ionization potentials and electron affinities of various atoms and molecules, workfunctions of metals, surface ionization efficiencies, and energies of vaporization of atoms and ions from various metal surfaces. .