PHYSICAL REVIEW A 86, 052706 (2012) Electron excitation of the 4 1 P 1 state of a zinc atom Mariusz Piwi´ nski, * Lukasz Klosowski, Dariusz Dziczek, and Stanislaw Chwirot Nicolaus Copernicus University, Institute of Physics, Grudzia ˛dzka 5/7, 87-100 Toru´ n, Poland Tapasi Das and Rajesh Srivastava Department of Physics, Indian Institute of Technology, Roorkee 247 667 Uttranchal, India A. D. Stauffer Department of Physics and Astronomy, York University, Toronto, Ontario, Canada M3J 1P3 Christopher J. Bostock, Dmitry V. Fursa, and Igor Bray ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia (Received 27 September 2012; published 19 November 2012) Experimental results of Stokes parameters and electron-impact coherence parameters for excitation of 4 1 P 1 state of zinc atoms are presented. The electron-photon coincidence method in the coherence-analysis version was applied to obtain data for scattering angles in the range from 5 ◦ to 40 ◦ for incident electron energy 100 eV. The experimental results are presented together with convergent-close-coupling-method and relativistic-distorted-wave-approximation theoretical predictions. DOI: 10.1103/PhysRevA.86.052706 PACS number(s): 34.80.Dp, 34.80.Pa I. INTRODUCTION Alkaline-earth metals and other atoms with two valence electrons outside a relatively inert core such as Zn, Ca, Cd, and Hg are very interesting objects for theoretical and experimental investigations of electronic collisions. The most detailed information about inelastic-scattering processes can be obtained in electron-photon coincidence measurements [e.g., Stokes parameters or electron-impact coherence parameters (EICPs)]. Due to the complexity and long time required for such experiments, the amount of available data on such collision systems is rather limited [1–11]. Therefore, more experimental results are still needed to test and develop the theoretical models. The present work is a continuation of our previous coincidence studies of electron scattering on Ca and Cd atoms [12–14]. The next target—zinc—has been investigated in experimental and theoretical studies of interactions with polarized electrons. Very interesting information on spin- dependent effects in formation of negative ions has been summarized in Ref. [15]. Some unexpected effects have been also revealed in 3 S 1 state excitation by polarized electrons [16], providing additional justification for coincidence experiments on Zn. The first set of coherence parameters for Zn atoms excited to the 4 1 P 1 state by electrons with incident energy of 100 eV is presented in this paper. The theoretical relativistic- distorted-wave approximation (RDWA) and convergent-close- coupling (CCC) predictions for the full range of scattering angles are also shown. II. APPARATUS The experimental setup used in the present work was essentially the same as the one used in experiments on * Mariusz.Piwinski@fizyka.umk.pl electron-impact excitation of cadmium atoms [14,17]. A diagram of the apparatus is shown in Fig. 1. The geometry of the experiment was typical for the coherence-analysis version of electron-photon coincidence measurements. The electron-atom collisions took place in a vacuum chamber with typical pressure of 5 × 10 −7 mbar with the Zn atomic beam effusing from a magnetically shielded oven. The electron and atomic beams were cross-fired, creating an interaction region of a diameter 1.5–2 mm located 22 mm above the two-stage collimator of the atom source. The typical operating temperatures of the oven were 341 ◦ C for the main reservoir and 355 ◦ C for the nozzle. Number density of the Zn atoms was of the order of 10 10 atoms/cm 3 in the interaction region. The electron beam of energy 100 eV and 3–6 μA of current was produced by a Comstock EG-402EL electron gun. A Comstock AC-901 electrostatic electron-energy analyzer was used for energy selection of the electrons scattered by atoms and observed at the fixed scattering angle . During coincidence measurements the analyzer transmitted electrons which had lost the energy corresponding to the excitation of Zn atoms from their ground to the 4 1 P 1 state. The combined energy resolution of the electron gun and the energy analyzer was about 0.7 eV. The acceptance angle of the electron detection channel was 0.06 rad. A typical energy-loss spectrum is shown in Fig. 2. Photons of the wavelength 213.8 nm emitted spontaneously by atoms relaxing from the 4 1 P 1 to their ground state were detected in the direction perpendicular to the scattering plane defined by the momenta of the impacting and the observed scattered electrons. The polarization state of the emitted radiation was determined with a custom-made pile-of-plates polarizer and a zero-order quartz retardation plate (Melles Griot). The acceptance angle of the photon detection channel was approximately 0.2 rad. The coincidence circuitry used in the experiment was the same as in the previous experiments on cadmium atoms [14]. A typical accumulated coincidence spectrum is shown in Fig. 3. 052706-1 1050-2947/2012/86(5)/052706(5) ©2012 American Physical Society