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Hellα photoelectron spectra of the valence p shells of K and Rb
Volu~ne 67. number I
CN3lICAL
PIIYSICS LLI-I-ERS
1 Novmber
1979
HeIIa PHOTOELECTRON SPECTRA OF THE \‘ALENCE p SHELLS OF K AND Rb A-W. POTTS 2nd E.P.F.
Rrcehcd
16 JuI)
LEE
1979
The IIcIIa photoelectron spcctrs ofatomic pot.Gurrt .utd rubidium arc reported. Valence p-’ ionization is discussed in terms of tinaf-st~tc configuration interxtion. Effects due to discharge contaniwtion b> the mersl rapours are noted.
I _ Introduction
We have recently reported the photoelectron specp sheli ionization in both atomic barium iI 1 and atomic caesium [2] _ In both these cases the spectrs differed considerably from those expected on the b,xis of simple p-l ionization ;LSa result of fin&state configuration interaction (CI) effects_ fisrtree-Fock cltIcuIations allowing for Ci have been carried out on the valence p-l states of K+ [3] and Rbf [4] ions. These indicate that the KII and Rbil states formed wiii also be subject to considerable CI effects. At the time of our caesium study [2], Heila spectra of rubidium and potassium were also recorded_ Ilowever. in both cases the spectra were considembly complicated by the presence cf valence shell S-I ionizstion on RbI and KI emission lines respectively. A similar effect had been observed in a previous Hero study of these metal vapours [5J _ In the case of potassium the spectrum was also complicated by the He Is-’ ionization line (fig_ I)_ Both of these effects arose from the fact tJlat in order to maximize He11 signa tile discharge tube is not efficiently isolated from the ionization region- The addition of differential pumping largely removed Iines due to both He Is-’ ionization and to RbI and Ki emission (figs. I. 2 and 3) and showed that the Mf p-’ states were well described by the Hartree-Fock calcuistions incIuding final state CL tra of valence
2. Experimental The experirnentd arrxgernent and techniques used were similar to those previously described [2 J_ However the 25.4 mm length by 1.5 mm diameter isolating capillary between the discharge and ionization region proved to be inadequate for the reasons aIready outlined. A number of lines in the spectra of both K and Rb were consistent with ionization of the metal ,lsl orbital by emission lines from the MI process ix* 2 S .- (11 - I)p5& ?P and Hitler Iines in this series [6,7] (figs. 1 and 3). It was assumed that these arose from diffusion of the metal vapour through the isotating capillary back to the hollow cathode discharge. This is surprising since a pseudo molecular beam apparatus was used with the discharge not on a Iine of si#t from the furnace tube. To test the assumption a further simiIar 25.4 mm isolating capillary ~3s introduced with a small diffusion pump providing differentkd pumping between the capillaries. This produced the improved spectra shown in figs. Ib, Zb and 3_ Spectra resuIting from the KI and RbI emission lines were Iargely eIiminated as was the He Is-’ ionization on HeMa. We note at this point that none of the Iines observed in the CsII spectmm [2] could be attributed to Csi emission lines which do not occur in the 5p-’ region_ In fact no such emission Iines were observed in this spectrum despite the absence of differential pumping Resolution in this work corresponded to measured half widths of 120 mV in the p-’ region. This value arises from 3 sIight Ioss of resolution as a result of con93
tanlination of the slit region by these rextire metal v+~urs old from use of iage sIit wi&hs for nr.r_xin~iun count mte. cl-_ figs. L-X
GenattI spectra of the r;lknce p-t region with rend without different&I pumping are shown in figs. I 2nd 2 anJ espalsions of the p-j region in fig, 3_ In Ule ~cnerd spectra. fkstures rfuc to IMa ionkrtion of K -ts ;urd Kb 5s cIcctrons are observed as well zs the previously identified K -KS-t autoionization on the UC& tIeIZi line [51_ The virtu31 absence of electron ener_* loss peaks associated with the principal pesks indiates that the beam pressure cannot be hi@ [S]_ lk principal features indicated in fig:. 3 are those associated with the valence p-t ionization_ As with the equivalent ionization for Cs tlartree-Fock c&x~kttions have shown that the final stxtrs correspoadin~ to this structure do not correspond to 0 simple (II - I)$‘& conf&rration but to states arising from interaction between the states formed by the configura-
20
22
24
26
IPCeVJ
Fig I_ General spectra of the 3p-’ ioniwtion region for K. (3) without differential pumping, (b) uith differential pumpins 94
tion (rrr- I)p’((rr - 1)d +ws)~ _ These caIcuIdtions have been used to m;lke assignments for Ii11 and RbiI emission spectrz Ionization potcntiaJs calculated from emission drtta are in esceknt agreement with the rcs&s obtained here (tables 1 and 2) and simikr assignments for the ionized st3tes are therefore assumed.
F%_ 3. DelSled
He&
&owin~ theoretinl
spectra of (a) Ii 3p-’ relative intensities-
and, (b)
Rb 4p-*
\‘oJumc 67. number I
CIK\IICAL
-I-.ibIe I Obser%ed ionization potenti.&
PIIYSJCS
I Norember
1979
(cV) and rehthe
intensity of the pflotoelectron peaks corresponding to various strttes is given by the percentage of tile state which can be assigned to tJle simple (H - l)p5nsf configuration witI an allowance for the 3_1 t I degeneracy of the state_ Relative intensities calculated in tJlis way taken from MtinsfieJd [3] for I(11 and Reader and Epstein [4] for RbJJ are given in tables 1 and 2 respectively together with the experimentaL intensities deduced from band areas. In botll czses the totnl intensities have been normaked to 100. In is clear tJlst agreement is excellent and well within the experimental error which could be 8s J&h 3s 10%. This justifies tJle origins1 assignments and indicates tJlat within tile sensitivity of tJle experiment the in-
Table 2 Observed ionization potenti.ds and rchtivr This r1ork IP (eV)
LC-ITCRS
rel. int.
f
intensities for the 4p-J
tensities are governed by final state configuration interaction effects. Theoretical relative intensities are aJso represented as bar spectra in fig_ 3 and can be seen to give a good representation of tile partially resolved structure for wJvilicJ1experimental intensities Jlave not been deduced. One apparent difference between the spectra reported here and tJlose for Cs ~3s the observation of 3 number of weak bands corresponding to states where the (II - l)p5,zs1 configuration played only B minor part. The absence of these states for I( and Rb possibly indicates the greater importance of CI for the heavy stem.
ionization of rubidium
Reader and Ep,tem
[4 J
IF (eV) 3)
xl_ int.
% 4p55s’
J
::*;;
4 16 I ‘12
48% 3P
0
4p54d’Szz
31%3P+15%~P
1
4p54d’
52% 3P
2
4p54d’
89% 3P
- _ 22.03
z
4%IP
m3jor
3P
a) Observed RbII energp IebeIs by Reader and Epstein [4]; Rb 5s -1 ionization taken to be 4.18 eV_ b)i - I notation brloss to the 4~~5s’ confi~untion_ 9.5
Vdumt
67. number
-I_ c011c1ti011
96
E
CWEM ICAL
PIfYSiCS
LIXITrRS
References
I x:or~,rnfxr
1979
CN3lICAL
PIIYSICS LLI-I-ERS
1 Novmber
1979
HeIIa PHOTOELECTRON SPECTRA OF THE \‘ALENCE p SHELLS OF K AND Rb A-W. POTTS 2nd E.P.F.
Rrcehcd
16 JuI)
LEE
1979
The IIcIIa photoelectron spcctrs ofatomic pot.Gurrt .utd rubidium arc reported. Valence p-’ ionization is discussed in terms of tinaf-st~tc configuration interxtion. Effects due to discharge contaniwtion b> the mersl rapours are noted.
I _ Introduction
We have recently reported the photoelectron specp sheli ionization in both atomic barium iI 1 and atomic caesium [2] _ In both these cases the spectrs differed considerably from those expected on the b,xis of simple p-l ionization ;LSa result of fin&state configuration interaction (CI) effects_ fisrtree-Fock cltIcuIations allowing for Ci have been carried out on the valence p-l states of K+ [3] and Rbf [4] ions. These indicate that the KII and Rbil states formed wiii also be subject to considerable CI effects. At the time of our caesium study [2], Heila spectra of rubidium and potassium were also recorded_ Ilowever. in both cases the spectra were considembly complicated by the presence cf valence shell S-I ionizstion on RbI and KI emission lines respectively. A similar effect had been observed in a previous Hero study of these metal vapours [5J _ In the case of potassium the spectrum was also complicated by the He Is-’ ionization line (fig_ I)_ Both of these effects arose from the fact tJlat in order to maximize He11 signa tile discharge tube is not efficiently isolated from the ionization region- The addition of differential pumping largely removed Iines due to both He Is-’ ionization and to RbI and Ki emission (figs. I. 2 and 3) and showed that the Mf p-’ states were well described by the Hartree-Fock calcuistions incIuding final state CL tra of valence
2. Experimental The experirnentd arrxgernent and techniques used were similar to those previously described [2 J_ However the 25.4 mm length by 1.5 mm diameter isolating capillary between the discharge and ionization region proved to be inadequate for the reasons aIready outlined. A number of lines in the spectra of both K and Rb were consistent with ionization of the metal ,lsl orbital by emission lines from the MI process ix* 2 S .- (11 - I)p5& ?P and Hitler Iines in this series [6,7] (figs. 1 and 3). It was assumed that these arose from diffusion of the metal vapour through the isotating capillary back to the hollow cathode discharge. This is surprising since a pseudo molecular beam apparatus was used with the discharge not on a Iine of si#t from the furnace tube. To test the assumption a further simiIar 25.4 mm isolating capillary ~3s introduced with a small diffusion pump providing differentkd pumping between the capillaries. This produced the improved spectra shown in figs. Ib, Zb and 3_ Spectra resuIting from the KI and RbI emission lines were Iargely eIiminated as was the He Is-’ ionization on HeMa. We note at this point that none of the Iines observed in the CsII spectmm [2] could be attributed to Csi emission lines which do not occur in the 5p-’ region_ In fact no such emission Iines were observed in this spectrum despite the absence of differential pumping Resolution in this work corresponded to measured half widths of 120 mV in the p-’ region. This value arises from 3 sIight Ioss of resolution as a result of con93
tanlination of the slit region by these rextire metal v+~urs old from use of iage sIit wi&hs for nr.r_xin~iun count mte. cl-_ figs. L-X
GenattI spectra of the r;lknce p-t region with rend without different&I pumping are shown in figs. I 2nd 2 anJ espalsions of the p-j region in fig, 3_ In Ule ~cnerd spectra. fkstures rfuc to IMa ionkrtion of K -ts ;urd Kb 5s cIcctrons are observed as well zs the previously identified K -KS-t autoionization on the UC& tIeIZi line [51_ The virtu31 absence of electron ener_* loss peaks associated with the principal pesks indiates that the beam pressure cannot be hi@ [S]_ lk principal features indicated in fig:. 3 are those associated with the valence p-t ionization_ As with the equivalent ionization for Cs tlartree-Fock c&x~kttions have shown that the final stxtrs correspoadin~ to this structure do not correspond to 0 simple (II - I)$‘& conf&rration but to states arising from interaction between the states formed by the configura-
20
22
24
26
IPCeVJ
Fig I_ General spectra of the 3p-’ ioniwtion region for K. (3) without differential pumping, (b) uith differential pumpins 94
tion (rrr- I)p’((rr - 1)d +ws)~ _ These caIcuIdtions have been used to m;lke assignments for Ii11 and RbiI emission spectrz Ionization potcntiaJs calculated from emission drtta are in esceknt agreement with the rcs&s obtained here (tables 1 and 2) and simikr assignments for the ionized st3tes are therefore assumed.
F%_ 3. DelSled
He&
&owin~ theoretinl
spectra of (a) Ii 3p-’ relative intensities-
and, (b)
Rb 4p-*
\‘oJumc 67. number I
CIK\IICAL
-I-.ibIe I Obser%ed ionization potenti.&
PIIYSJCS
I Norember
1979
(cV) and rehthe
intensity of the pflotoelectron peaks corresponding to various strttes is given by the percentage of tile state which can be assigned to tJle simple (H - l)p5nsf configuration witI an allowance for the 3_1 t I degeneracy of the state_ Relative intensities calculated in tJlis way taken from MtinsfieJd [3] for I(11 and Reader and Epstein [4] for RbJJ are given in tables 1 and 2 respectively together with the experimentaL intensities deduced from band areas. In botll czses the totnl intensities have been normaked to 100. In is clear tJlst agreement is excellent and well within the experimental error which could be 8s J&h 3s 10%. This justifies tJle origins1 assignments and indicates tJlat within tile sensitivity of tJle experiment the in-
Table 2 Observed ionization potenti.ds and rchtivr This r1ork IP (eV)
LC-ITCRS
rel. int.
f
intensities for the 4p-J
tensities are governed by final state configuration interaction effects. Theoretical relative intensities are aJso represented as bar spectra in fig_ 3 and can be seen to give a good representation of tile partially resolved structure for wJvilicJ1experimental intensities Jlave not been deduced. One apparent difference between the spectra reported here and tJlose for Cs ~3s the observation of 3 number of weak bands corresponding to states where the (II - l)p5,zs1 configuration played only B minor part. The absence of these states for I( and Rb possibly indicates the greater importance of CI for the heavy stem.
ionization of rubidium
Reader and Ep,tem
[4 J
IF (eV) 3)
xl_ int.
% 4p55s’
J
::*;;
4 16 I ‘12
48% 3P
0
4p54d’Szz
31%3P+15%~P
1
4p54d’
52% 3P
2
4p54d’
89% 3P
- _ 22.03
z
4%IP
m3jor
3P
a) Observed RbII energp IebeIs by Reader and Epstein [4]; Rb 5s -1 ionization taken to be 4.18 eV_ b)i - I notation brloss to the 4~~5s’ confi~untion_ 9.5
Vdumt
67. number
-I_ c011c1ti011
96
E
CWEM ICAL
PIfYSiCS
LIXITrRS
References
I x:or~,rnfxr
1979