The valence photoelectron satellite spectra of Kr and Xe

Journal of Electron Spectroscopy and Related Phenomena 114–116 (2001) 141–146 www.elsevier.nl / locate / elspec

The valence photoelectron satellite spectra of Kr and Xe ¨ T. Matila, K. Vaarala, H. Aksela, S. Aksela S. Alitalo*, A. Kivimaki, Department of Physical Sciences, P.O. Box 3000, FIN-90014 University of Oulu, Oulu, Finland Received 8 August 2000; received in revised form 31 August 2000; accepted 6 September 2000

Abstract Photoelectron spectra of Kr and Xe were measured with high resolution in the region of ns 2 np 4 n9l (n54 for Kr, n55 for Xe) states. Experimental results are compared with optical data, with previous photoelectron studies and with configuration interaction calculations. A number of previously unobserved photoelectron satellites were detected. Some new assignments for the photoelectron satellite lines, particularly for Kr, are suggested.  2001 Elsevier Science B.V. All rights reserved. Keywords: Photoionization; Photoelectron satellites; Kr; Xe

1. Introduction The electronic states of rare gases in different electronic configurations are of special interest in atomic and molecular physics since they are relatively simple and thus serve as tests for different theoretical approaches. In addition to optical spectroscopies, photoelectron spectroscopy is one of the most important methods when studying singly ionized atoms. It was found in the 1960s that multiple excitation and ionization events may occur during photoionization [1]. These events can be divided into correlation and shakeup transitions. The former are due to a strong interaction between the close lying states of different configurations but the same parity while the latter normally arise from nl → ml (m . n) monopole shake-up transitions accompanying photoionization. Satellite transitions are observed in photo*Corresponding author. Tel.: 1358-8-553-1329; fax: 1358-8553-1287. E-mail address: [email protected] (S. Alitalo).

electron spectra as peaks with lower kinetic energies than that of the related main photoelectron line. A large collection of the photoelectron satellite spectra of the rare gases excited with monokromatized Al K a radiation was published by Svensson et al. [2]. More recently, the valence photoelectron spectra have mostly been studied using synchrotron radiation. Krause et al. [3] presented photoelectron spectra of Ne, Ar, Kr and Xe for low excitation energies of about 65 eV and resolved in each case about 30 ns 2 np 4 n9l correlation satellites (n signifies the principal quantum number of the highest occupied orbital and n9 $ n). The measurements of Kikas et al. [4] were performed with still higher overall instrumental resolution and they also covered the ns 1 np 5 n9l and ns 0 np 6 n9l correlation satellites. ¨ Carlsson-Gothe et al. [5] measured the Xe 5s photoelectron spectrum with He II a (40.8 eV) radiation and observed almost 80 5s 2 5p 4 n9l correlation satellites. In the present paper, the outermost correlation satellites (ns 2 np 4 n9l) of Kr and Xe were measured at hn 5125 eV. Despite the higher photon energy, a

0368-2048 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0368-2048( 00 )00277-2

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higher total instrumental resolution was achieved than in the previous studies [3–5]. Consequently, a number of previously unobserved correlation satellites were detected.

2. Experimental The experiments were performed on the new undulator beamline I411 [6] at the 1.5 GeV MAX–II storage ring at Lund, Sweden. Radiation in the photon energy range from 50 eV to well above 1000 eV is monochromatized by a modified SX–700 plane grating monochromator. The Kr 4s and Xe 5s photoelectron satellite spectra were measured at 125 eV photon energy in the binding energy regions of 43.65–27.12 and 38.56–22.53 eV, respectively. The use of a 10-mm exit slit for the monochromator resulted in a photon resolution of | 15 meV. Electrons ejected at 54.78 upwards from the electric vector of the incident light were recorded with a

rotatable SES–200 hemispherical analyzer. A 10 eV pass energy gave a kinetic energy resolution of about 20 meV. The total line widths of the main photoelectron lines were found to be | 27 meV. The spectra were corrected for the spectrometer transmission which was determined with the method described in Ref. [7]. The binding energy scale was calibrated using the energy values given by Minnhagen et al. [8] and Hansen and Persson [9].

3. Results The photoelectron spectra of Kr 4s and Xe 5s are presented in Fig. 1(a) and (b), respectively. A leastsquares fit of Voigt functions was applied to determine the energies and intensities of the lines. The line shapes were constrained to be the same for all lines in each spectrum. The satellite lines in the photoelectron spectra were identified by comparing the fit results to the designations given by Moore

Fig. 1. (a) The Kr 4s and (b) Xe 5s photoelectron satellite spectra measured at 125.0 eV photon energy. Intensities are scaled so that the Kr 4s and Xe 5s photoelectron lines have peak heights of 100.

S. Alitalo et al. / Journal of Electron Spectroscopy and Related Phenomena 114 – 116 (2001) 141 – 146

[10], Minnhagen et al. [8], Hansen and Persson [9] and Kikas et al. [4], and to the results of configuration interaction (CI) calculations. The consistency of the assignments was also checked by comparing the results for Kr and Xe with each other. The energies, intensities and assignments of the photoelectron satellite lines of Kr and Xe are presented in Tables 1 and 2, respectively. The energies of previously unobserved satellites and the new assignments are written in boldface. We performed a CI calculation including LSJ states from the ns 1 np 6 and ns 2 np 4 (nd 2 20d,(n 1 1)s 2 21s) configurations using the Cowan’s code [11] and the method described in Ref. [12]. For ns 2 np 4 n9 p states, which were not calculated, we used the assignments found in resonant Auger spectroscopy [13–16]. Only few of the states can be assumed to be nearly pure LS states. Usually they are a complex mixture of several LS states and / or different configurations. Mixing between the states given in Tables 1 and 2 is denoted with a ‘‘1’’ sign while overlapping states are separated by commas. The most intense satellites are the ( 1 D)nd( 2 S1 / 2 ) lines which gain intensity because of strong configuration interaction with the ns 1 np 6 ( 2 S1 / 2 ) state. It was possible to identify several such satellites even with high n values. Also the other states (np 4 n9s,n9d, J51 / 2) arising from CI are quite strong. The intensities of the shake-up satellites (np 4 n9 p, J51 / 2,3 / 2) are slightly lower than those of the CI satellites. Furthermore, many satellites of the same configurations as given above, but with higher J values were found. Their appearance relates to the influence of channel interactions in which scattering wavefunctions that include the escaping electron can mix leading to the mixing of the ionic states with the different angular momentum. The photoelectron satellites appearing through CI have about 75% of the satellite intensity while 20% and 5% remain for the shake-up satellites and the channel interaction states, respectively. The total relative intensity of all the ns 2 np 4 n9l satellites is much higher in Xe (122) than in Kr (62). This can be explained by the greater overlap of the wavefunctions of Xe (Z554) as compared to Kr (Z536). The many-electron effects therefore become stronger with increasing Z. In conclusion, high-resolution photoelectron spectra for Kr 4s and Xe 5s were recorded and analysed

143

Table 1 The assignment of lines in the Kr 4s photoelectron spectrum Eb / eV

Int.

Kr assignment

27.512 28.270 28.579 28.688 28.999 29.817 29.852 30.056

100.00 0.12 0.28 0.09 0.15 0.19 0.33 0.08

30.228 30.318 30.487 30.651 30.689

1.01 0.04 0.10 0.03 0.16

30.998 31.156 31.224 31.374 31.571 31.605 31.655 31.949 32.080 32.496 32.538 32.561 32.623

0.17 0.68 0.59 0.21 0.10 0.17 0.07 0.05 2.04 0.10 0.47 0.11 3.66

4s4p 6 ( 2 S1 / 2 ) 4p 4 ( 3 P)5s( 4 P3 / 2 ) ( 3 P)5s( 4 P1 / 2 ) ( 3 P)5s( 2 P3 / 2 ) ( 3 P)5s( 2 P1 / 2 ),( 3 P)4d( 4 D3 / 2 ) ( 1 D)5s( 2 D3 / 2 ) ( 1 D)5s( 2 D5 / 2 ),( 3 P)4d( 4 F7 / 2 ) ( 3 P)4d( 2 P1 / 2 ) 1 ( 4 P1 / 2 ) 1( 1 D)4d( 2 P1 / 2 ) ( 3 P)4d( 4 P1 / 2 ) 1 ( 2 P1 / 2 ) ( 3 P)4d( 2 F7 / 2 ) ( 3 P)4d( 2 P3 / 2 ),( 4 P5 / 2 ) ( 3 P)5p( 4 P3 / 2 ) ( 3 P)4d( 2 D3 / 2 )1( 1 D)5s( 2 D3 / 2 ) 1( 1 D)4d( 2 D3 / 2 ),( 3 P)4d( 2 F 5 / 2 ) ( 3 P)4d( 2 D5 / 2 )1( 1 D)4d( 2 D5 / 2 ) ( 3 P)5p( 2 D3 / 2 ) ( 3 P)5p( 2 P1 / 2 ) ( 3 P)5p( 4 D5 / 2 ),( 2 P3 / 2,1 / 2 ) ( 3 P)5p( 4 S3 / 2 ) ( 3 P)5p( 4 D3 / 2 ) ( 3 P)5p( 4 D1 / 2 )

32.823 32.874

0.28 2.69

33.573 33.935 34.013

0.03 17.98 0.03

34.068 34.154 34.213 34.386 34.468 34.598 34.697 34.821 34.858 34.906 34.946 35.028

2.92 1.10 0.11 3.17 0.12 0.32 0.11 0.06 0.19 0.12 0.34 0.25

35.062

0.02

( 1 S)5s( 2 S1 / 2 ) ( 1 D)5p( 2 F5 / 2 ) ( 1 D)4d( 2 D5 / 2 )1( 3 P)4d( 2 D5 / 2 ) ( 1 D)5p( 2 F7 / 2 ) ( 1 D)5p( 2 P3 / 2 ), ( 1 D)4d( 2 P3 / 2 )1( 3 P)4d( 2 P3 / 2 ) ( 1 D)4d( 2 D 3 / 2 ) ( 1 D)4d( 2 P1 / 2 )1( 3 P)5d( 2 P1 / 2 ) 1( 3 P)4d( 2 P1 / 2 ), ( 1 D)5p( 2 D3 / 2 ),( 2 P1 / 2 ),( 2 D5 / 2 ) ( 3 P)6s( 2 P3 / 2 ) ( 1 D)4d( 2 S1 / 2 ) ( 1 S)4d( 2 D3 / 2 )1( 3 P)5d( 4 P3 / 2 ) 1( 3 P)5d( 4 D3 / 2 ),( 3 P)5d( 4 D5 / 2 ) ( 3 P)6s( 4 P1 / 2 ),( 4 P3 / 2 ) 1 ( 4 D3 / 2 ) ( 3 P)5d( 4 D1 / 2 ) 1 ( 4 P1 / 2 ),( 2 F 7 / 2 ) ( 3 P)6s( 2 P1 / 2 ) ( 1 S)6s( 2 S1 / 2 ) ( 3 P)5d( 4 P3 / 2 ),( 3 P)6p( 4 D5 / 2 ) ( 3 P)6p( 4 D1 / 2 ) ( 3 P)5d( 2 P1 / 2 ),( 4 F 3 / 2 ),( 2 F5 / 2 ) ( 3 P)5d( 2 P3 / 2 ) ( 1 S)5p( 2 P1 / 2 ),( 3 P)4f ( 3 P)6p,( 3 P)4f ( 1 S)5p( 2 P3 / 2 ) ( 3 P)6p, ( 3 P)5d( 2 D5 / 2 )1( 3 P)6d( 2 D5 / 2 ) ( 3 P)6p

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S. Alitalo et al. / Journal of Electron Spectroscopy and Related Phenomena 114 – 116 (2001) 141 – 146

Table 1. Continued Eb / eV

Int.

Kr assignment

35.146

0.31

35.185 35.321 35.521 35.811 35.868 35.996 36.037 36.105

0.27 0.07 0.02 0.02 0.07 0.03 0.04 0.06

( 3 P)6p,( 3 P)5d( 2 D3 / 2 ) 1( 3 P)6d( 2 D3 / 2 )1( 1 S)4d( 2 D3 / 2 ) ( 3 P)6p ( 3 P)6p,( 1 D)6s( 2 D3 / 2 ) ( 3 P)7s( 2 P3 / 2 ),( 3 P)4f ( 1 D)5d( 2 G7 / 2 ), ( 3 P)6d( 4 F7 / 2 )

36.129 36.161 36.186 36.238 36.277 36.325 36.372 36.468 36.520 36.635 36.723 36.756 37.131 37.181 37.214 37.310 37.368 37.542 37.576 37.725 37.763 37.795 37.831 37.893 37.955 38.023 38.150 38.480 38.507 38.542 38.587 38.628 38.982 39.030 39.267 39.300 39.459 39.489 39.609 39.645 39.700 39.775 39.839

0.02 0.04 0.11 0.36 0.19 0.01 0.80 7.45 0.09 0.69 0.18 0.18 0.04 0.04 0.02 0.03 0.02 0.21 0.08 0.15 0.10 0.17 3.19 0.20 0.07 0.04 0.19 0.09 0.19 1.55 0.07 0.13 1.00 0.08 0.58 0.07 0.39 0.04 0.35 0.03 0.25 0.21 0.16

( 1 D)5d( 2 P3 / 2 )1( 3 P)6d( 2 P3 / 2 ) ( 1 D)5d( 2 D5 / 2 )1( 3 P)6d( 2 F5 / 2 ) 1( 3 P)6d( 4 F5 / 2 ) ( 1 D)5d( 2 P1 / 2 ) ( 3 P)7s( 2 P1 / 2 ) 1 ( 4 P1 / 2 ) ( 1 D)6p ( 1 D)6p,( 3 P)7p ( 3 P)7p ( 1 D)5d( 2 S 1 / 2 ) ( 3 P)7p ( 3 P)7p ( 3 P)8p ( 3 P)8p ( 3 P)9p ( 3 P)9p ( 3 P)8p

( 1 D)7p ( 1 D)7p ( 1 D)7p ( 1 D)6d( 2 S 1 / 2 ) ( 3 P)9p ( 3 P)10p ( 1 S)6p ( 1 D)7d( 2 S 1 / 2 ),( 1 D)8p ( 1 D)8d( 2 S 1 / 2 ) ( 1 D)10p ( 1 D)9d( 2 S 1 / 2 ) ( 1 D)10d( 2 S 1 / 2 ) ( 1 D)11p ( 1 D)11d( 2 S 1 / 2 ) ( 1 D)12d( 2 S 1 / 2 ) ( 1 D)13d( 2 S 1 / 2 ) ( 1 D)14d( 2 S 1 / 2 )

Table 2 The assignment of lines in the Xe 5s photoelectron spectrum Eb / eV

Int.

Xe assignment

23.398 23.670 23.738 23.840 23.872 23.915 23.968 24.009 24.036 24.150 24.456 24.562 24.598 24.674 24.718 25.057

100.00 0.07 0.39 0.61 0.20 0.07 0.14 0.06 0.26 0.11 0.08 0.06 0.20 5.67 0.15 0.88

5s5p 6 ( 2 S1 / 2 ) 5p 4 ( 3 P)6s( 4 P5 / 2 ) inelastic peak inelastic peak

25.185

0.28

25.268 25.335 25.387 25.440 25.522 25.715 26.103 26.134 26.201 26.231 26.359 26.380 26.613 26.899 27.061 27.115 27.156 27.211 27.416 27.516 27.545

3.98 0.09 2.87 0.04 0.12 0.21 0.14 0.50 0.03 0.11 0.16 1.04 3.11 0.10 0.08 0.07 0.06 0.06 0.87 0.48 0.47

27.578 27.881 27.945 28.109 28.157 28.209 28.258 28.489 28.523 28.590 28.650

0.29 10.41 0.23 0.36 3.27 4.39 0.36 0.48 0.05 5.36 0.02

( 3 P)6s( 2 P3 / 2 ) 1 ( 4 P3 / 2 ) ( 3 P)5d( 4 D5 / 2,7 / 2 ) ( 3 P)5d( 4 D3 / 2 ) ( 3 P)5d( 4 D1 / 2 ) ( 3 P)5d( 4 F9 / 2 ) ( 3 P)6s( 4 P1 / 2 ) ( 3 P)5d( 2 F7 / 2 ) 1 ( 4 F7 / 2 ) ( 3 P)5d( 2 P1 / 2 )1( 3 P)6s( 2 P1 / 2 ) 1( 1 D)5d( 2 P1 / 2 ) ( 3 P)5d( 2 D3 / 2 )1( 1 D)5d( 2 D3 / 2 ) 1( 3 P)5d( 4 F3 / 2 ) ( 3 P)5d( 4 P1 / 2 ) ( 3 P)5d( 4 F5 / 2 ) ( 3 P)6s( 2 P1 / 2 ) ( 3 P)5d( 4 F3 / 2 ) ( 3 P)5d( 4 P3 / 2,5 / 2 ) ( 1 D)6s( 2 D5 / 2 ) ( 3 P)5d( 2 F5 / 2 ) ( 1 D)6s( 2 D3 / 2 ) ( 3 P)6p( 2 D5 / 2 ) ( 3 P)6p( 2 S1 / 2 ),( 4 D7 / 2 ) ( 1 D)5d( 2 D5 / 2 ) ( 1 D)5d( 2 G9 / 2,7 / 2 ) ( 3 P)6p( 2 P3 / 2 ) ( 1 D)5d( 2 F5 / 2 ) ( 3 P)6p( 2 P1 / 2 ) ( 1 D)5d( 2 F7 / 2 ) ( 3 P)6p( 4 P1 / 2 ) ( 3 P)6p( 2 D3 / 2 ) ( 3 P)6p( 4 S3 / 2 ) ( 1 D)5d( 2 P3 / 2 )1( 3 P)5d( 2 P3 / 2 ) ( 3 P)6p( 4 D3 / 2 ),( 3 P)5d( 2 D5 / 2 ) 1( 1 D)5d( 2 D5 / 2 )1( 3 P)6d( 2 D5 / 2 ) ( 3 P)6p( 4 D1 / 2 ) ( 1 D)5d( 2 P1 / 2 )1( 3 P)6d( 2 P1 / 2 ) ( 1 D)5d( 2 D3 / 2 ) ( 1 D)6p( 2 F5 / 2 ) ( 1 S)6s( 2 S1 / 2 ) ( 1 D)6p( 2 P3 / 2 ) ( 1 D)6p( 2 F7 / 2 ) ( 1 D)6p( 2 D3 / 2 ) ( 1 D)6p( 2 D5 / 2 ) ( 1 D)6p( 2 P1 / 2 ) ( 3 P)7s( 2 P3 / 2 )

S. Alitalo et al. / Journal of Electron Spectroscopy and Related Phenomena 114 – 116 (2001) 141 – 146 Table 2. Continued

Table 2. Continued Eb / eV

Int.

Xe assignment

Eb / eV

Int.

28.877 29.007 29.062

17.81 0.04 6.91

29.246 29.331 29.383

0.12 13.77 0.11

29.447

0.12

29.492 29.528 29.609 30.228

0.22 0.27 1.23 0.02

( 1 D)5d( 2 S1 / 2 ) ( 3 P)6d( 4 F9 / 2 ) ( 3 P)6d( 2 P1 / 2 ) 1 ( 4 D1 / 2 ), ( 1 S)5d( 2 D5 / 2 ),( 3 P)6d( 2 F7 / 2 ) ( 1 S)5d( 2 D3 / 2 ) ( 3 P)6d( 4 P1 / 2 ) ( 3 P)6d( 2 D5 / 2 ) 1 ( 2 F5 / 2 ) 3 2 3 4 1( P)7d( D5 / 2 ),( P)4f( D5 / 2 ), 3 4 ( P)7p( D5 / 2,3 / 2 ) ( 3 P)6d( 4 P3 / 2 ) 1 ( 2 D3 / 2 ), ( 3 P)7p( 4 P5 / 2,7 / 2 ) ( 3 P)7p( 4 P1 / 2 ) ( 3 P)4f( 4 P3 / 2 ) ( 3 P)7s( 4 P1 / 2 ),( 3 P)7p( 4 P3 / 2 ) ( 3 P)6d( 2 D3 / 2 ) 1 ( 2 P3 / 2 ) 1( 4 D3 / 2 ) 1 ( 4 F3 / 2 ) ( 3 P)6d( 4 P5 / 2 )1( 3 P)6d( 2 F5 / 2 ) ( 3 P)8s( 2 P3 / 2 ),( 3 P)7p, ( 3 P)4f( 2 F5 / 2 ),( 2 P7 / 2 ) ( 3 P)7p 1 2 3 ( S)6p( P1 / 2 ),( P)7p, 3 2 ( P)6d( P3 / 2 )1( 1 D)6d( 2 P3 / 2 ) 1( 3 P)7d( 2 D3 / 2 )

32.525 32.550 32.644 32.705 32.745 32.770 32.799 32.823 32.857 32.890 32.918 32.972 33.059 33.180 33.241 33.441 33.468 33.531 33.561 33.590 33.645 33.673 33.795 33.882 33.921 34.004 34.032 34.086 34.316 34.390 34.510 34.549 34.650 34.749 34.826 34.886 34.937

0.06 0.08 0.05 0.05 0.14 0.18 1.34 0.91 1.05 0.26 0.24 0.43 0.33 0.14 0.08 0.09 0.08 0.25 0.54 1.29 0.17 0.16 0.27 0.38 0.22 0.52 0.83 0.14 0.80 0.07 0.48 0.14 0.40 0.32 0.25 0.22 0.20

30.271 30.427

0.02 0.07

30.470 30.506

0.07 0.35

30.578 30.648 30.676 30.706 30.760 30.785 30.834 30.892 31.072 31.170

0.16 0.63 0.55 0.03 0.19 1.08 0.03 0.38 0.08 0.07

31.222 31.270 31.407 31.490 31.591 31.624

0.01 1.32 1.99 8.97 0.42 0.95

31.796 31.832 31.893 31.922 31.940 31.977 32.026 32.071 32.200 32.248 32.392 32.428

0.09 0.32 0.11 0.19 0.08 0.08 0.22 0.25 0.20 0.07 0.11 0.07

145

1

2

1

2

1

2

3

2

( S)6p( P3 / 2 ),( P)4f( P7 / 2 ) 3

( D)7s( D3 / 2 ),( P)4f [3]5 / 2 3 ( P)5f [5]9 / 2 3 ( P)8p 3 ( P)8p ( D)6d( G7 / 2,9 / 2 ) ( 1 D)6d( 2 P3 / 2 ) 1 ( 2 D3 / 2 ) 3 2 1 2 1( P)7d( D3 / 2 ),( D)6d( F5 / 2 ) 1 2 2 ( D)6d( F7 / 2 ),( D5 / 2 ) 1 2 ( D)6d( P1 / 2 ) 1 1 2 ( D)7p,( D)4f( D3 / 2 ) 1 2 ( D)6d( S 1 / 2 ),( 1 D)7p,( 3 P)9p ( 3 P)6g ( 3 P)8s( 2 P1 / 2 ),( 1 D)7p, ( 3 P)9p,( 1 D)4f ( 3 P)8p

Xe assignment

( 3 P)9p ( 1 D)8p ( 1 D)8p ( 1 D)7d( 2 S 1 / 2 ),( 1 D)8p ( 1 D)8p ( 1 D)8p ( 1 D)8p,( 3 P)10p ( 1 D)8p,( 3 P)10p

( 1 D)9p ( 1 D)9p ( 1 D)9p ( 1 D)8d( 2 S 1 / 2 ),( 1 D)9p ( 1 D)9p ( 1 D)9p

( 1 S)7p ( 1 D)9d( 2 S 1 / 2 ), ( 1 S)7p, ( 1 D)10p ( 1 D)10p ( 1 D)10d( 2 S 1 / 2 ) ( 1 D)11d( 2 S 1 / 2 ) ( 1 D)12d( 2 S 1 / 2 ) ( 1 D)13d( 2 S 1 / 2 ) ( 1 D)14d( 2 S 1 / 2 ) ( 1 D)15d( 2 S 1 / 2 ) ( 1 D)16d( 2 S 1 / 2 )

in detail. Many new satellites and assignments were found. These results provide an important reference for further theoretical studies.

( 3 P)5g( 4 P7 / 2,9 / 2 )

Acknowledgements

( 3 P)9p ( 3 P)9p

The staff of MAX-laboratory is acknowledged for assistance during the measurements. This work has been supported by the Research Council for the Natural Sciences of the Academy of Finland.

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