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Cross sections and angular distributions of the photoelectron correlation satellites of the the Xe atom
Journal of Electron Spectroscopy and Related Phenomena 79 (1996) 315-318
Cross sections and angular distributions of the photoelectron correlation satellites of the the Xe atom S. B. Whitfield~, B. Langerb, J. Viefhaus¢, R. Wehlitzd, N. Berrah b , U. Becker c , B. M. Lagutine, I. D. Petrov e and V. L. Sukhorukov¢ ~Department of Chemistry, University of Nevada, Las Vegas NV, 89154-4003 bDepartment of Physics, University of Western Michigan, Kalamazoo MI, 49009 eFritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin, Germany dDepartment of Physics, University of Tennessee, Knoxville TN, 37996 eRostov State University of Transport Communication, Rostov-on-Don 344017, Russia A high resolution electron spectrometry study of the sub-valence 5s-photoelectron correlation satellites of Xe is presented. We report both absolute partial cross sections and angular distributions of several selected satellite lines recorded at photon energies from 40.8 eV up to 150 eV. Our high resolution results are compared to earlier lower resolution measurements and to our calculations which incorporate both configuration interaction and many-body perturbation theory techniques.
The 5s-photoionization satellite spectrum of Xe has attracted both experimental and theoretical interest for nearly twenty years. With the advent of tunable synchrotron radiation sources, the experimental spectra of these satellites has improved steadily revealing ever more detailed and and complicated structure. Concurrently, refinement in theoretical models and methods has also progressed so that the behavior of the same correlation satellites in the lighter rare gases Ne and Ar, is quite well understood. However, a correct description of the behavior of these satellites in the heavier rare gases, Kr and in particular Xe, poses a more serious challenge to theory. In this report we will present additional results from our recent high-resolution measurements of Xe that were not published earlier [1]. We will compare our absolute partial cross sections, a, and angular distribution parameters, /3, of selected satellites with previous lower resolution measurements and with our calculations which incorporate both many-body perturbation theory, configuartion interaction and inter-shell correlations.
undulator beam line BW3 utilizing a high resolution SX-700 monochromator [2]. The measurements were carried out during single- and double-bunch operation of the electron storage ring. Electrons produced in the interaction region were simultaneously detected by two time-offlight (TOF) electron spectrometers with a nominal resolving power of about 100 which was significantly enhanced by application of a strong retarding potential to the entrance of the TOF analyzers. Both analyzers are mounted on a rotatable chamber perpendicular to the axis of the incoming radiation to Mlow for the determination of angular distributions. In order to compare previous lower resolution data with our high resolution results, it was necessary to rescale the lower resolution data in order to remove the contribution of neighboring satellite lines. This rescaling procedure was carried out only for the experimental data above a photon energy of 40.8 eV, since we recorded no spectra below that energy. Finally, measured intensities between the satellite lines and the 5s-main line were placed on an absolute scale by using measured values of the 5s-cross section [3-5]
2. E X P E R I M E N T
3. T H E O R Y
The experiment was performed at the Hamburger Synchrotronstrahlungslabor (HAYSLAB) on the
To obtain photoionization cross sections and angular distribution parameters for the correlation
1. I N T R O D U C T I O N
0368-2048/96/$15.00 ~ 1996 Elsevier Science B.V. All rights reserved PII S0368 2048 (96) 02862-9
316
satellites, it was necessary to calculate energies and wave functions of the initial Xe I and final Xe II states and to determine the transition amplitudes between these states accounting for many-body effects. Several techniques have been applied in the present calculations: configuration interaction theory, many-body perturbation theory, and non-orthogonal orbital theory. All bound-state wave functions were constructed using the non-relativistic Hartree-Fock approximation, while the continuum electron wave functions were obtained from the relativistic ttartee-FockPauli equation. A detailed description of the theoretical methods used in our calculations will be published elsewhere [6].
.8 eV
~1
.0
lJ r A
x4
h~ = 6 0 . 0 e V
A x,
h
~
x4
.
A
x4
I^
-,20.v
h~ = SS.0 eV
I~ = I00.0 eV
h~ = 1 2 5 . 0
4. R E S U L T S A N D D I S C U S S I O N Magic angle spectra recorded at each photon energy investigated, following a time-to-energy conversion and transmission correction are displayed in figure 1. Spectra recorded at the magic angle are independent of angular distribution effects, and serve as a direct measure of relative partial cross sections providing the spectra have been corrected for transmission effects. As the resolution of the TOF analyzer varies monotonically as a function of kinetic energy, the full-widthhalf-maximum (FWttM) of every line in a given spectrum is different. Thus, the 5s-main line in the spectrum recorded at 72 eV has a FWHM of 138(5) meV, while the peak with a binding energy of about 31.5 eV has a FWHM of 86 meV. Because the spectrum recorded at 150 eV coincides with the second Cooper minimum in the Xe 5s-cross section, where the overall spectral intensity is nearly two orders of magnitude lower than at 85 eV [5], it was necessary to alter both the incident photon flux and the retarding voltage to obtain a measurable signal. Both effects led to a significant degradation in the resolution. Figure 1 illustrates the change of the satellite lines as the photon energy is varied from 40.8 to 150.0 eV. From about 60 eV up to 125 eV, the overall structure of the satellites with respect to the main line remains essentially the same. The largest changes occur between 40.8 and 60 eV and between 125 and 150 eV. While the appearance of much of the spectrum at 150 eV is similar to those recorded between 60 and 125 eV, several .
eV
x4
23
24
.
25
26
27
28
^
29
eV
h~ = 1 5 0 . 0 e V
30
31
32
33
Binding Energy (eV) Figure 1: Overview of the Xe 5s-PES recorded at the magic angle and various photon energies.
satellite lines which were much weaker in intensity are now of a magnitude comparable to the strongest satellite lines. For example, those satellites between a binding energy of about 26 and 27 eV, and those between about 30 and 31 eV. This behavior is undoubtedly related to the appearance at this photon energy of the second Cooper minimum in the 5s-photoionization cross section. In figure 2 we compare our calculated 5s-PES at a photon energy of 72 eV with our measured spectrum recorded at the same energy. All satellites have been designated according to the scheme of Krause el al. [7]. Lines without numbers indicate features that we clearly observe that were not seen in the spectrum of ref. [7]. The calculated spectrum in the upper portion of figure 2 has been convoluted by a Gaussian of varying FWHM to simulate the resolution of the TOF spectrometer. As can be seen, there is rather good agreement between theory and experiment. However, there are several noticeable differences. For example, theory predicts almost no intensity for satellite 4, which is of comparable magnitude
317
to satellite 3. Theory also predicts satellite 7 to be substantially stronger than satellite 6, which is clearly not observed in the experimental spectrum. The calculated energies and strengths of the odd and even satellite 9 do not match experiment where only one feature is seen. This inaccuracy has been traced to our calculated energies of the (3p)5d 2D5/~ and the (1D)5d 2P3/2 configurations which comprise the theoretical peak 9% Presumably, improved calculations will redistribute the components of this peak into its neigbours, satellites 9 ° and 10. Additional discrepancies between theory and experiment will be addressed below.
2.0 ~-
1.6 1.2
! .
.
.
.
Sat. 13
0.10 -~ :~
~" 0.0S 0.00 2 ¢~. t 0 -1 10"1 10.= t~
/
~
.
/
,.
.
~
A - '~
/ _
t
.\
.
.
.
.
~
e,o..t.l.~]
:
:
I
. , h = , r [0]
:
.
• °xp.--o,,k3. "~ n Fahlman gtm£ [4)
' ~ ~(3 ~ ~ .
exp.--~IQ.
[] Fahirmm,B,"a/.[4]-'
\
•
10-s
•
,'t BrlonetaL[8] Kratmeetnl[7] .
.
.
.
.
.
.---.,..
qe
.
2
I 5s I
I ' I Xe 5s-PES hv = 7 2 e V
I
I
¢~"
theory
0
t o~..--=,. J
/'~
10"2! ~ 10"s . ] 10"41. i 7
~3 j 1~5
10
26
,
: 50
c
24
1
[ . . . .
~ :
. . . .
~-t---.
9e
I
X4
O Knmteeta/. [7}
28
~
experiment
2[
30
32
100
150
P h o t o n e n e r g y (eV)
34
Figure 3: Comparison of our calculated a and/~ values (solid curve) to our measurements (filled circles) and earlier measurements for sats. 13, 9 and 8. Calculations were performed for the primary component only of each satellite.
Binding Energy (eV)
Figure 2: Calculated 5s-PES for an incident photon energy of 72 eV compared to our experimental 5s-PES. Of particular interest is the behavior of the various satellite cross sections and angular distributions as a function of photon energy. This is illustrated in figure 3 by a representative satellite from three different satellite "groups," namely an even satellite with a total final-ionic momentum of J = 1/2 (sat. 13), an odd satellite (sat. 9) and an even satellite with J > 1/2 (sat. 8). The upper portion of figure 3 compares our calculated cr and ~ values for satellite 13, primary component 5p4(1D)5d 2S1/2 , with our measured values and those of earlier experiments. The agreement between our high resolution results and the rescaled cross sections of the lower resolution data is excel-
lent. In the case of/3, however, our value at 40.8 eV does not agree with the trend of the data from Fahlman et al. [4]. This is due to the overlap of the second order 4d3/2 photoline with satellite 13 at this energy. Although we have corrected for this overlap by subtracting this photoline from the data, we still do not consider our ~ value at this energy to be very reliable. Discrepancies with the measurements of Mahler [9] are due to the contribution of unresolved lines in his spectra which have ~ values different from satellite 13. The results of our theoretical calculations are in reasonable agreement with the experimental data. The difference between the calculated and measured maximum of satellite 13 is mainly due to inaccuracies in the calculation of the multiconfiguration ionic eigenfunction for this satellite. In the case of ~, the reason for the discrepancies
318 are less clear, but may be related to the use of non-relativistic atomic-core orbitals. The middle panel of figure 3 corresponds to satellite 9 whose primary configuration according to our calculations is 5p4(3P)6p 2D3/2. Again there is excellent agreement between the various experimental values. Despite the fact that our our calculation consistently underestimates the cross section of this line, the agreement with experiment is nevertheless quite satisfactory. It is not as good for/3, although the qualitative behavior is quite well reproduced. The/3 and ~ behavior for this line is primarily determined by the interference of two outgoing partial waves, es and ed in contrast to satellite 13, and all even satellites with J = 1/2, where only an outgoing ep wave is allowed. For this reason this satellite should behave very similarly to the 5p lines, which is infact the case [6]. Satellites with even ionic states and J > 1/2 are characterized by two possible outgoing partial waves, ep and el. Thus, as in the case of the odd satellites, their cr and fl behavior should be qualitatively different from that of the even satellites with J - 1/2. This is shown in the bottom panel of figure 3 for satellite 8 whose assignment corresponds to the 5p4(1D)5d 2F5/2 configuration. Due to the very weak nature of this line, see figure 2, it was only possible to obtain accurate experimental values of ~ and/3 up to 85 eV. There is considerable discrepancy between our measurement and that of Krause et al. [7] at 72 eV. The reason for this discrepancy is not clear, but probably attributable to the lower resolution in their work. Although there is good qualitative agreement between theory and experiment, our experimental ~r values are consistently lower than theory, and our j3 values indicate larger variations. However, for such a weak satellite, an accurate determination of the background can often be very difficult. Hence, a systematic overestimation of the background for this line could explain some of the discrepancies with theory. 5. S U M M A R Y We have presented a high resolution electron spectrometry study of the Xe sub-valence correlation satellites from a photon energy of 40.8
to 150.0 eV. We have also carried out a theoretical treatment of these satellites which simultaneously incorporates configuration interaction, many-body perturbation theory and inter-shell correlations. We have compared our experimental results for a few select satellites with qualitatively different a and/~ behavior to earlier, lower resolution measurements and to our calculations. In most instances there is excellent agreement amongst the various experiments and generally good accord between theory and experiment. AKNOWLEDGMENTS As the work for this project took place in Germany, SBW and NB would like to thank the Humboldt foundation for a fellowship, BML the Deutsche Forschungsgemeinschaft for financial support and VLS the Max-Planck-Society for a fellowship. This work was also supported by the Bundesministerium fiir Forschung und Technologic under contract no. 05 5EBFXB 2. REFERENCES
1. S. B. Whitfield, B. Langer, J. Viefhaus, R. Wehlitz, N. Berrah, W. Mahler and U. Becket, J. Phys B: At. Mol. Opt. Phys. 27, L359 (1994). 2. T. MSller, Synchrotron Radiat. News 6, 16 (1993). 3. M. Y. Adam, F. Wuilleumier, N. Sandner, V. Schmidt and G. Wendin, J. Physique 39, 129 (1978) 4. A. Fahlman, M. O. Krause, T. A. Carlson and A. Svensson, Phys. Rev. A 30, 812 (1994). 5. U. Becker, D. Szostak, H. G. Kerhoff, M. Kupsch, B. Langer, R. Wehlitz, A. Yagishita and T. Hayaishi, Phys. Rev. A 39, 3902 (1989). 6. B. M. Lagutin, I. D. Petrov, V. L. Sukhorukov, S. B. Whitfield, B. Langer, J. Viefhaus, R. Wehlitz, N. Berrah and U. Becker, submitted to J. Phys B: At. Mol. Opt. Phys. 7. M. O. Krause, S. B. Whitfield, C. D. Caldwell, J-Z. Wu, P. van der Meulen, C. A. de Lange and R. W. C. Hansen, J. Elec. Spec. Rel. Phen. 58, 79 (1992). 8. C. E. Brion, A. O. Bawagan and K. H. Tan, Can J. Chem. 66, 1877 (1988). 9. W. Mahler, Diplomarbeit Technische Universit~t Berlin, unpublished.
Cross sections and angular distributions of the photoelectron correlation satellites of the the Xe atom S. B. Whitfield~, B. Langerb, J. Viefhaus¢, R. Wehlitzd, N. Berrah b , U. Becker c , B. M. Lagutine, I. D. Petrov e and V. L. Sukhorukov¢ ~Department of Chemistry, University of Nevada, Las Vegas NV, 89154-4003 bDepartment of Physics, University of Western Michigan, Kalamazoo MI, 49009 eFritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin, Germany dDepartment of Physics, University of Tennessee, Knoxville TN, 37996 eRostov State University of Transport Communication, Rostov-on-Don 344017, Russia A high resolution electron spectrometry study of the sub-valence 5s-photoelectron correlation satellites of Xe is presented. We report both absolute partial cross sections and angular distributions of several selected satellite lines recorded at photon energies from 40.8 eV up to 150 eV. Our high resolution results are compared to earlier lower resolution measurements and to our calculations which incorporate both configuration interaction and many-body perturbation theory techniques.
The 5s-photoionization satellite spectrum of Xe has attracted both experimental and theoretical interest for nearly twenty years. With the advent of tunable synchrotron radiation sources, the experimental spectra of these satellites has improved steadily revealing ever more detailed and and complicated structure. Concurrently, refinement in theoretical models and methods has also progressed so that the behavior of the same correlation satellites in the lighter rare gases Ne and Ar, is quite well understood. However, a correct description of the behavior of these satellites in the heavier rare gases, Kr and in particular Xe, poses a more serious challenge to theory. In this report we will present additional results from our recent high-resolution measurements of Xe that were not published earlier [1]. We will compare our absolute partial cross sections, a, and angular distribution parameters, /3, of selected satellites with previous lower resolution measurements and with our calculations which incorporate both many-body perturbation theory, configuartion interaction and inter-shell correlations.
undulator beam line BW3 utilizing a high resolution SX-700 monochromator [2]. The measurements were carried out during single- and double-bunch operation of the electron storage ring. Electrons produced in the interaction region were simultaneously detected by two time-offlight (TOF) electron spectrometers with a nominal resolving power of about 100 which was significantly enhanced by application of a strong retarding potential to the entrance of the TOF analyzers. Both analyzers are mounted on a rotatable chamber perpendicular to the axis of the incoming radiation to Mlow for the determination of angular distributions. In order to compare previous lower resolution data with our high resolution results, it was necessary to rescale the lower resolution data in order to remove the contribution of neighboring satellite lines. This rescaling procedure was carried out only for the experimental data above a photon energy of 40.8 eV, since we recorded no spectra below that energy. Finally, measured intensities between the satellite lines and the 5s-main line were placed on an absolute scale by using measured values of the 5s-cross section [3-5]
2. E X P E R I M E N T
3. T H E O R Y
The experiment was performed at the Hamburger Synchrotronstrahlungslabor (HAYSLAB) on the
To obtain photoionization cross sections and angular distribution parameters for the correlation
1. I N T R O D U C T I O N
0368-2048/96/$15.00 ~ 1996 Elsevier Science B.V. All rights reserved PII S0368 2048 (96) 02862-9
316
satellites, it was necessary to calculate energies and wave functions of the initial Xe I and final Xe II states and to determine the transition amplitudes between these states accounting for many-body effects. Several techniques have been applied in the present calculations: configuration interaction theory, many-body perturbation theory, and non-orthogonal orbital theory. All bound-state wave functions were constructed using the non-relativistic Hartree-Fock approximation, while the continuum electron wave functions were obtained from the relativistic ttartee-FockPauli equation. A detailed description of the theoretical methods used in our calculations will be published elsewhere [6].
.8 eV
~1
.0
lJ r A
x4
h~ = 6 0 . 0 e V
A x,
h
~
x4
.
A
x4
I^
-,20.v
h~ = SS.0 eV
I~ = I00.0 eV
h~ = 1 2 5 . 0
4. R E S U L T S A N D D I S C U S S I O N Magic angle spectra recorded at each photon energy investigated, following a time-to-energy conversion and transmission correction are displayed in figure 1. Spectra recorded at the magic angle are independent of angular distribution effects, and serve as a direct measure of relative partial cross sections providing the spectra have been corrected for transmission effects. As the resolution of the TOF analyzer varies monotonically as a function of kinetic energy, the full-widthhalf-maximum (FWttM) of every line in a given spectrum is different. Thus, the 5s-main line in the spectrum recorded at 72 eV has a FWHM of 138(5) meV, while the peak with a binding energy of about 31.5 eV has a FWHM of 86 meV. Because the spectrum recorded at 150 eV coincides with the second Cooper minimum in the Xe 5s-cross section, where the overall spectral intensity is nearly two orders of magnitude lower than at 85 eV [5], it was necessary to alter both the incident photon flux and the retarding voltage to obtain a measurable signal. Both effects led to a significant degradation in the resolution. Figure 1 illustrates the change of the satellite lines as the photon energy is varied from 40.8 to 150.0 eV. From about 60 eV up to 125 eV, the overall structure of the satellites with respect to the main line remains essentially the same. The largest changes occur between 40.8 and 60 eV and between 125 and 150 eV. While the appearance of much of the spectrum at 150 eV is similar to those recorded between 60 and 125 eV, several .
eV
x4
23
24
.
25
26
27
28
^
29
eV
h~ = 1 5 0 . 0 e V
30
31
32
33
Binding Energy (eV) Figure 1: Overview of the Xe 5s-PES recorded at the magic angle and various photon energies.
satellite lines which were much weaker in intensity are now of a magnitude comparable to the strongest satellite lines. For example, those satellites between a binding energy of about 26 and 27 eV, and those between about 30 and 31 eV. This behavior is undoubtedly related to the appearance at this photon energy of the second Cooper minimum in the 5s-photoionization cross section. In figure 2 we compare our calculated 5s-PES at a photon energy of 72 eV with our measured spectrum recorded at the same energy. All satellites have been designated according to the scheme of Krause el al. [7]. Lines without numbers indicate features that we clearly observe that were not seen in the spectrum of ref. [7]. The calculated spectrum in the upper portion of figure 2 has been convoluted by a Gaussian of varying FWHM to simulate the resolution of the TOF spectrometer. As can be seen, there is rather good agreement between theory and experiment. However, there are several noticeable differences. For example, theory predicts almost no intensity for satellite 4, which is of comparable magnitude
317
to satellite 3. Theory also predicts satellite 7 to be substantially stronger than satellite 6, which is clearly not observed in the experimental spectrum. The calculated energies and strengths of the odd and even satellite 9 do not match experiment where only one feature is seen. This inaccuracy has been traced to our calculated energies of the (3p)5d 2D5/~ and the (1D)5d 2P3/2 configurations which comprise the theoretical peak 9% Presumably, improved calculations will redistribute the components of this peak into its neigbours, satellites 9 ° and 10. Additional discrepancies between theory and experiment will be addressed below.
2.0 ~-
1.6 1.2
! .
.
.
.
Sat. 13
0.10 -~ :~
~" 0.0S 0.00 2 ¢~. t 0 -1 10"1 10.= t~
/
~
.
/
,.
.
~
A - '~
/ _
t
.\
.
.
.
.
~
e,o..t.l.~]
:
:
I
. , h = , r [0]
:
.
• °xp.--o,,k3. "~ n Fahlman gtm£ [4)
' ~ ~(3 ~ ~ .
exp.--~IQ.
[] Fahirmm,B,"a/.[4]-'
\
•
10-s
•
,'t BrlonetaL[8] Kratmeetnl[7] .
.
.
.
.
.
.---.,..
qe
.
2
I 5s I
I ' I Xe 5s-PES hv = 7 2 e V
I
I
¢~"
theory
0
t o~..--=,. J
/'~
10"2! ~ 10"s . ] 10"41. i 7
~3 j 1~5
10
26
,
: 50
c
24
1
[ . . . .
~ :
. . . .
~-t---.
9e
I
X4
O Knmteeta/. [7}
28
~
experiment
2[
30
32
100
150
P h o t o n e n e r g y (eV)
34
Figure 3: Comparison of our calculated a and/~ values (solid curve) to our measurements (filled circles) and earlier measurements for sats. 13, 9 and 8. Calculations were performed for the primary component only of each satellite.
Binding Energy (eV)
Figure 2: Calculated 5s-PES for an incident photon energy of 72 eV compared to our experimental 5s-PES. Of particular interest is the behavior of the various satellite cross sections and angular distributions as a function of photon energy. This is illustrated in figure 3 by a representative satellite from three different satellite "groups," namely an even satellite with a total final-ionic momentum of J = 1/2 (sat. 13), an odd satellite (sat. 9) and an even satellite with J > 1/2 (sat. 8). The upper portion of figure 3 compares our calculated cr and ~ values for satellite 13, primary component 5p4(1D)5d 2S1/2 , with our measured values and those of earlier experiments. The agreement between our high resolution results and the rescaled cross sections of the lower resolution data is excel-
lent. In the case of/3, however, our value at 40.8 eV does not agree with the trend of the data from Fahlman et al. [4]. This is due to the overlap of the second order 4d3/2 photoline with satellite 13 at this energy. Although we have corrected for this overlap by subtracting this photoline from the data, we still do not consider our ~ value at this energy to be very reliable. Discrepancies with the measurements of Mahler [9] are due to the contribution of unresolved lines in his spectra which have ~ values different from satellite 13. The results of our theoretical calculations are in reasonable agreement with the experimental data. The difference between the calculated and measured maximum of satellite 13 is mainly due to inaccuracies in the calculation of the multiconfiguration ionic eigenfunction for this satellite. In the case of ~, the reason for the discrepancies
318 are less clear, but may be related to the use of non-relativistic atomic-core orbitals. The middle panel of figure 3 corresponds to satellite 9 whose primary configuration according to our calculations is 5p4(3P)6p 2D3/2. Again there is excellent agreement between the various experimental values. Despite the fact that our our calculation consistently underestimates the cross section of this line, the agreement with experiment is nevertheless quite satisfactory. It is not as good for/3, although the qualitative behavior is quite well reproduced. The/3 and ~ behavior for this line is primarily determined by the interference of two outgoing partial waves, es and ed in contrast to satellite 13, and all even satellites with J = 1/2, where only an outgoing ep wave is allowed. For this reason this satellite should behave very similarly to the 5p lines, which is infact the case [6]. Satellites with even ionic states and J > 1/2 are characterized by two possible outgoing partial waves, ep and el. Thus, as in the case of the odd satellites, their cr and fl behavior should be qualitatively different from that of the even satellites with J - 1/2. This is shown in the bottom panel of figure 3 for satellite 8 whose assignment corresponds to the 5p4(1D)5d 2F5/2 configuration. Due to the very weak nature of this line, see figure 2, it was only possible to obtain accurate experimental values of ~ and/3 up to 85 eV. There is considerable discrepancy between our measurement and that of Krause et al. [7] at 72 eV. The reason for this discrepancy is not clear, but probably attributable to the lower resolution in their work. Although there is good qualitative agreement between theory and experiment, our experimental ~r values are consistently lower than theory, and our j3 values indicate larger variations. However, for such a weak satellite, an accurate determination of the background can often be very difficult. Hence, a systematic overestimation of the background for this line could explain some of the discrepancies with theory. 5. S U M M A R Y We have presented a high resolution electron spectrometry study of the Xe sub-valence correlation satellites from a photon energy of 40.8
to 150.0 eV. We have also carried out a theoretical treatment of these satellites which simultaneously incorporates configuration interaction, many-body perturbation theory and inter-shell correlations. We have compared our experimental results for a few select satellites with qualitatively different a and/~ behavior to earlier, lower resolution measurements and to our calculations. In most instances there is excellent agreement amongst the various experiments and generally good accord between theory and experiment. AKNOWLEDGMENTS As the work for this project took place in Germany, SBW and NB would like to thank the Humboldt foundation for a fellowship, BML the Deutsche Forschungsgemeinschaft for financial support and VLS the Max-Planck-Society for a fellowship. This work was also supported by the Bundesministerium fiir Forschung und Technologic under contract no. 05 5EBFXB 2. REFERENCES
1. S. B. Whitfield, B. Langer, J. Viefhaus, R. Wehlitz, N. Berrah, W. Mahler and U. Becket, J. Phys B: At. Mol. Opt. Phys. 27, L359 (1994). 2. T. MSller, Synchrotron Radiat. News 6, 16 (1993). 3. M. Y. Adam, F. Wuilleumier, N. Sandner, V. Schmidt and G. Wendin, J. Physique 39, 129 (1978) 4. A. Fahlman, M. O. Krause, T. A. Carlson and A. Svensson, Phys. Rev. A 30, 812 (1994). 5. U. Becker, D. Szostak, H. G. Kerhoff, M. Kupsch, B. Langer, R. Wehlitz, A. Yagishita and T. Hayaishi, Phys. Rev. A 39, 3902 (1989). 6. B. M. Lagutin, I. D. Petrov, V. L. Sukhorukov, S. B. Whitfield, B. Langer, J. Viefhaus, R. Wehlitz, N. Berrah and U. Becker, submitted to J. Phys B: At. Mol. Opt. Phys. 7. M. O. Krause, S. B. Whitfield, C. D. Caldwell, J-Z. Wu, P. van der Meulen, C. A. de Lange and R. W. C. Hansen, J. Elec. Spec. Rel. Phen. 58, 79 (1992). 8. C. E. Brion, A. O. Bawagan and K. H. Tan, Can J. Chem. 66, 1877 (1988). 9. W. Mahler, Diplomarbeit Technische Universit~t Berlin, unpublished.