Excitation functions of Cd III 4d85s2 (Beutler) states by electron impact on Cd atoms

Volume l14A, number 4

PHYSICS LETTERS

17 February 1986

E X C I T A T I O N F U N C T I O N S OF Cd III 4dS5s" (BEUTLER) STATES BY E L E C T R O N I M P A C T O N Cd A T O M S S. I N A B A

a,

K. H A N E b and T. G O T O b

a Department of Electrical Engineering, Gifu National College of Technology, Motosu, Gifu 501-04, Japan h Department of Electronics, Faculty of Engineering, Nagoya University, Nagoya 464, Japan

Received 25 September 1985; revised manuscript received 3 December 1985; accepted for publication 4 December 1985

Emission cross sections for the lines from Cd III 4d85s2 (Beutler) states by single electron impact on Cd atoms have been measured in the electron energy region of 40-250 eV. The measured values are of the order of 10-19 cm2.

For the quantitative studies on the excitation mechanisms of various devices using a rare gas-Cd mixture discharge such as the He-Cd laser, it is important to measure the excitation cross sections for excited states of Cd ions by electron impact. Many investigations have been performed on emission cross sections of spectral lines transiting from Cd II excited states formed by single electron impact between Cd atoms and electrons [ 1 - 4 ] . However, the investigations on those from Cd III states have never been performed because of the weakness of the spectral lines. Previously, we have measured the direct-excitation cross sections for Cd II excited states by electron impact by using a photon-counting system of high sensitivity controlled by a minicomputer and have obtained the fact that the shapes of the optical excitation functions for the 441.6,325.0 and 353.5 nm lines from the 4d95s 2 (Beutler) states are different from those for the lines from the 4dl°nl states [5]. In this work, optical excitation functions of Cd III 4d 85 s2 (Beutler) states by single electron impact on Cd atoms have been measured in the electron energy region of 4 0 250 eV. Moreover, the absolute values of the emission cross sections at the electron energy of 160 eV have been determined. The experimental apparatus was the same as that used in our previous investigations [5,6]. The details were described there. Cd atoms were excited by single electron impact in the energy region of 4 0 - 2 5 0 eV. Photons emitted from the Cd III 4d85s 2 states were 0.375-9601/86/$ 03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

measured with the photon counting technique. In order to determine the absolute value of the emission cross sections Qi/for one Cd III line transiting from the state i to the state j, the photon count rate of the Cd II 274.9 nm line was also measured as a reference. The absolute emission cross section of this line was determined to be 7.4 X 10 -19 cm 2 with an uncertainty of-+24% at the electron energy of 160 eV in our previous work [6]. The relative sensitivity of the optical detection system was calibrated with a tungsten lamp and a deuterium lamp. The uncertainty of this relative calibration was estimated to be -+3.5% at 2 1 0 700 um and -+5% at 190-210 nm. Since the signal count was proportional to the Cd vapour pressure (of the order of 10 -5 Torr) and electron current, it was confirmed that only single collision processes occurred dominantly. Fig. 1 shows the optical excitation functions for six lines from Cd III 4d85s 2 states. The shapes were independent of the Cd vapour pressure under our experimental conditions. The uncertainty of the shape of each optical excitation function is less than +-3% in the region of 100-200 eV. All of them reach maxima around 150 eV and then are almost constant. It should be noticed that the shapes of these optical excitation functions are similar to those for the 441.6,353.5 and 325.0 nm lines from the Cd II 4d95s 2 inner-sheU electron excitation states (Cd II Beutler ground states) and are very different from those for lines from the Cd II 4dl°nl states [5]. It would be expected that the Cd III 201

Volume 114A, number 4

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Fig. 1. Excitation functions for the lines from 4da5s 2 states: 276.7 ( a F 4 - 5 p aDa), 250.0 (3F4-5 p aF4) , 208.8 (aF3-5 p aF3) , 280.6 ( 3 F 3 - 5 p 1D2), 261.9 ( a F 2 - 5 p 3D1) and 303.6 ( 3 F 4 - 5 p 1F3).

4d 85s 2 states are formed exclusively by the removal of two electrons of the inner-shell 4d 10 electrons (Cd III Beutler ground states). Then the shapes of these optical excitation functions should be those normally ascribed to ionization. Table 1 shows the absolute values of the emission cross sections Qi] for 10 lines from the 4d85s 2 (Beutler) states, which were measured at an electron

Table 1 Emission cross sections Qij for the lines from 4d85s 2 states at the electron energy of 160 eV. Transition

Wavelength (rim)

Qi/ (10 -19 cm 2)

erel (%)

Cabs (%)

5s 2 1D2 - 5 p 1P 1 5s 2 1D2 - 5 p XF3

190.92 191.00 j

3.23

12.0

27

5s2 3F 2 - 5 p aD 1 5s 2 3 F 3 - 5 p l D 2 5s23Fa-5paD3 5s 2 a F 3 - 5 p a F 3 5s2 3 F 3 - 5 p a F 4 5s2 a F 4 - 5 p 3 D a 5s 2 a F 4 - 5 p 1F3 5s 2 3 F 4 - 5 p a F 4

261.9 280.6 242.6 208.8 221.8 276.7 303.6 250.0

2.41 2.61 1.09 4.54 1.03 6.61 1.49 5.93

4.8 4.6 4.8 5.8 10.4 4.6 5.3 4.5

24 24 24 25 26 24 25 24

202

energy of 160 eV. The ere 1 is the uncertainty of the relative value of Qi/which was obtained by combining in quadrature uncertainties of the calibrated relative sensitivity of the detection system and the signal count S. In this paper, the uncertainty of S is defined as (N +S)1/2/S, where N is the noise count and (N + S)I/2 is the standard deviation of the Poisson statistics of the total count N + S. The uncertainty Cab s of the absolute value of Qli was obtained by combining in quadrature ere 1 and the uncertainty (+--24%) of the absolute emission cross section of the Cd II 274.9 nm line used as a reference. The authors would like to express their thanks to Mr. T. Kito for his assistance in this experiment. [1] R.J. Anderson and E.T.P. Lee, J. Chem. Phys. 53 (1970) 754. [2] P. Varshavskii, A.A. Mityureva and N.P. Penkin, Opt. Spectrosc. 29 (1970) 111. [3] V.S. Aleinikov and V.V. Vshakov, Opt. Spectrosc. 29 (1970) 111. [4] I.P. Bogdanova, S.V. Ryazantseva and V.E. Yakhontova, Opt. Speetrosc. 45 (1978) 622. [5] T. Goto, K. Hane, M. Okuda and S. Hattori, Phys. Rev. A27 (1983) 1844. [6] T. Goto, K. Hane and S. Hattori, Phys. Rev. A29 (1984) 111.