Ireneusz Linert

Measurements of differential cross sections for elastic electron scattering in the backward direction by molecular oxygen

Absolute differential cross sections have been measured for elastic electron scattering by molecular oxygen in the backward direction over the scattering-angle range 100°–180°, at selected incident energies in the range 7–20 eV. These measurements employed the magnetic angle-changing technique with a newly designed conical-solenoid source for the localized magnetic field. The measured differential cross sections are presented together with previous experimental work and the results of theoretical calculations. Integrated elastic and momentum transfer cross sections have been deduced using the measured differential cross sections for backward scattering together with existing differential cross sections for forward scattering.

A study of electron impact excitation of molecular oxygen at a scattering angle of 180

Abstract Excitation of molecular oxygen by electron impact has been observed at the backward scattering angle of 180°. For these studies a new solenoid system with a conical geometry has been designed to implement the angle-changing technique. Energy loss spectra have been measured to deduce differential cross-sections for vibrational excitation of the X 3 Σ g − ground state and excitation of the a 1 Δ g state at 180°. Excitation of the b 1 Σ g + state has not been observed at 180° in agreement with the theoretically predicted selection rule Σ − ←↦Σ + at that angle.

Electronic states of tetrahydrofuran molecules studied by electron collisions

Electronic states of tetrahydrofuran molecules were studied in the excitation energy range 5.5-10 eV using the technique of electron energy loss spectroscopy in the gas phase. Excitation from the two conformations, C(2) and C(s), of the ground state of the molecule are observed in the measured energy loss spectra. The vertical excitation energies of the (3)(n(o)3s) triplet state from the C(2) and C(s) conformations of the ground state of the molecule are determined to be 6.03 ± 0.02 and 6.25 ± 0.02 eV, respectively. The singlet-triplet energy splitting for the n(o)3s configuration is determined to be 0.31 eV. It is also found that excitation from the C(s) conformation of the ground state has a higher cross section than that from the C(2) conformation.

Differential cross sections for electron impact vibrational excitation of molecular oxygen in the angular range 15°–180°

Absolute differential cross sections have been measured for excitation of the v = 1–4 vibrational levels of the X3Σg− ground state of molecular oxygen at an electron impact energy of 10 eV in a wide scattering angle range, from 15° to 180°. In the measurements, a recently constructed double hemispherical electron spectrometer has been used which employs the magnetic angle-changing technique to observe the backward scattering of electrons. The integral excitation cross sections for the above vibrational levels have been also determined through integration of the measured differential cross sections. A detailed comparison of the obtained cross sections has been made with the results of previous measurements.

Differential cross sections for electron elastic scattering and vibrational v = 1 excitation in nitrogen in the energy range from 5 to 20 eV measured over an angular range of 10°–180°

Absolute differential cross sections for elastic electron scattering and vibrational, v = 0 → 1, excitation in nitrogen have been measured in the scattering angle range from 10° to 180° and at incident electron energies between 5 eV and 20 eV. The magnetic angle-changing technique has been applied to access the range of scattering angles between 90° and 180°. Integral and momentum cross sections have also been derived by integration of the measured differential cross sections. A comparison with recent theoretical calculations of elastic and vibrational cross sections is presented.

Ionization and fragmentation of furan molecules by electron collisions

Cation mass spectra obtained by electron impact were measured to investigate the ionization and ionic fragmentation of furan, C4H4O, molecules in the gas phase. The most abundant cations, with comparable intensities in the mass spectra, were the parent, C4H4O+, cation (68 amu) and the C3H3+ fragment (39 amu). The appearance energies of most of the observed ionic fragments were determined and the possible fragmentation processes are discussed. The electron-impact absolute total and partial ionization cross sections in furan were measured using the total ion collection technique over the energy range from the respective ionization thresholds to 150 eV.

Electron impact fragmentation of pyrrole molecules studied by fluorescence emission spectroscopy

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Elastic electron scattering in neon in the 110 degree sign -180 degree sign scattering angle range

Differential cross sections for elastic electron scattering in neon have been measured in the angular range of backward scattering from 110 degree sign -180 degree sign at incident energies of 7, 10, and 15 eV. These measurements combined the use of a magnetic angle changer and an electrostatic electron spectrometer. The differential cross sections measured in the above scattering angle range, together with results obtained previously in the range below 110 degree sign , have been integrated to obtain integral elastic and momentum transfer cross sections. Detailed comparison is presented of the measured differential and integral cross sections with the results of various theoretical calculations.