Transitions W ithin the n = 4 Com plex of K rV II Obtained from a Theta-Pinch Light Source

T h e spectru m o f six tim es ion ized k ryp ton (K r V II) has been ob served in th e 4 3 0 -1 0 0 0 A w avelen gth range and 23 lines have been identified a s transition s b etw een levels o f the 4 s2, A sA d . A p 2 and A sA p con figu ra tion s. F o r 13 o f the lin es th e c la ssifica tion is new . R ev ised va lu es are prop osed for three leve ls w h ile for th e rest th e u n certain ty in the ex ist in g level v a lu e s has been co n s id era b ly decreased . T h e resu lts are su p p orted by iso elec tro n ic com p arison s a lo n g th e Z n 1 iso e lec tro n ic seq uence. T h e con figu ra tion s are interpreted by fittin g the th eo retica l energy exp ression s to the ob served energy levels u sin g leastsq u a res tech n iq u es. T h e param eter va lu es are com p ared w ith resu lts from H a r tr e e -F o c k ca lcu la tion s.


Introduction
The K r6* ion belongs to the Zn I isoelectronic sequence.The knowledge of the spectra in this sequence with the exception of the Z n l spectrum was for a long time limited [1].A small number of levels were reported for G a ll-B r V I [1], but for K r V II and more highly ionized ions, no information was available.For Zn I the analysis presented in Atomic Energy Levels [1] has been extended [2][3][4], and a few levels of G a ll [5] were added by Denne et al.Recently Isberg and Litzen revised and extended the analysis of Ga II [6].The analyses of SeV and B rV I have also been extended [7,8].For more highly ionized ions the 4 s-4p resonance transition of Rb V III-M o X III and R u X V -D y X X X V II was observed by Reader and Acquista [9,10].Litzen and Ando reported the 4 s-4 p transitions including intercombination lines in Z rX I, N b X II and Mo X III [11].Observations of the K r V II spectrum were reported by Fawcett et al. using a zeta-pinch [12].Several reports on observations of K r V II spectra using the beam-foil technique [13][14][15][16] have appeared.The Zn I isoelec tronic sequence has been studied theoretically in a number of papers [17][18][19][20].
The present work concerns the study of the 4r, 4s4d, 4p 2 and 4s4p configurations in K rV II.
The revival of the interest in data on the Zn I isoelectronic sequence is due to observations of impurity-lines from highly ionized heavy ions with few valence electrons in high tem perature plasmas [21,22]

Experimental arrangements
The light source used in the present work is a theta-pinch discharge built at Lund Institute of Technology [24], The spectra were recorded using a 3 m normal-incidence spectrograph equipped with a 1200 lines/mm grating blazed for 1380 A. The plate factor in the first diffraction order is 2.77 A mm-1.
To distinguish between different stages of ionization, a number of experimental parameters, i.e., gas pressure, dis charge voltage and number of discharges, were varied.A well developed K r V II spectrum was obtained with the following parameters: 4mTorr, 13kV and 800 discharges.
The spectra were exposed on Kodak SW R plates and lines from C III, N III, O III, K r I I and K r I I I were used as internal standards.The plates were measured with a semi-automatic comparator with a photoelectric setting device [25].For sharp lines the settings are reproducible to within ± 0.5 p m .Third order interpolation formulas, together with correction curves, were employed to reduce the comparator settings to wavelength values.The accuracy of the wavelength values is estimated to be ±0.01 A.

Analysis
The K r V II lines observed in the present work are given in Table 1,13 of them being without previous classification.The intensity figures given in the table are based on visual estimates.
The energy levels derived from the observed lines are given in Table II, and the general structure of the term system is shown in Fig. 1

. When establishing the energy levels, we were guided by isoelectronic comparisons taking into account Zn I [1], G a ll [6], G e III [1], A s IV [1], SeV [7] and B rV I [7, 8].
When performing the analysis we also used theoretical predictions of the structures of the configurations.The predictions were obtained by diagonalizing the energy matrices with appropriately scaled Hartree-Fock (HF) values for the energy parameters.For this purpose the computer code developed by Cowan [26] was used.A comparison with the level system given by Pinnington et al. [16] shows that eight of their levels values have been confirmed, although the accuracy has been considerably improved.However, for three levels we propose new identifications as discussed below. For

.
Such lines have been used for diagnostic purposes.The resonance transition 4s* ,S0-4s4p ]P, has been observed for a large range of Z values in the Zn I isoelectronic sequence [9, 23].* P e r m a n e n t ad d ress: U N 1 C A M P , I n stitu to d e F ísica D E Q -P la sm a , 1 3 1 0 0 C a m p iñ a s S P , B rasil.* P e r m a n e n t ad d ress: C e n tr o d e I n v e stig a c io n e s O p tic a s (C IO p ), L a P la ta .A r g e n tin a .

Fig. I .
Fig. I.The gross structure of the lower part o f the KrVIII energy level system.

the level 4s4p yP 0 we propose the new value 117389 cm-1. The level is established from a line at 617.18 A, classified as the 4s4p 3P0-4p2 \P, transition. This position is in reasonable agreement with the value predicted by Curtis [20]. For the level 4j4rf3Z>, we propose a new value at 349973 c m '1 . The level is determined by a line at 558.22 A Table I. Identified lines o f Kr VII Intensity ¿(À) a (cm 1 )
* Asymmetric line.classified as the 4s4p 'P t-4 s4 d 3D { transition.

This identifi cation is confirmed by the lines at 435.01 A and 447.60 A corresponding to the 4s4p
[19]-4 s4 d 3£>, and 4s4p 3P2~4s4d iD ] transitions.This new level value is in agreement with the theoretically predicted value by Ivanova et al.[19].For the level 4p 2 'D 2 we

propose the value 279 714 cm"1 , determined by a line at 918.45 A and classified as the 4s4p 'P, - 4p2 lD 2 transition. The identification is confirmed by a line at 626.48 A classified as 4s4p
3P l-4p2 lD 2 and a line at 652.90A classified as 4s4p 3P 2-4 p 2 'D 2. This

Table III . Energy parameters for the 4s4p configuration o f Kr VII Parameter HF value (cm-1) Fitted value* (cm -1)
* The rms deviation of the fit is 17cm" 1 for 4 observed levels.*The