HIGH RESOLUTION STUDY OF RYDBERG STATES
OF BARIUM
E. Eliel, W. Hogervorst
To cite this version:
E. Eliel, W. Hogervorst.
HIGH RESOLUTION STUDY OF RYDBERG STATES
OF BARIUM. Journal de Physique Colloques, 1982, 43 (C2), pp.C2-443-C2-446.
<10.1051/jphyscol:1982236>. <jpa-00221848>
HAL Id: jpa-00221848
https://hal.archives-ouvertes.fr/jpa-00221848
Submitted on 1 Jan 1982
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JOURNAL DE PHYSIQUE
Colloque
C2, supplément
au n°ll,
Tome 43, novembre
1982
page
C2-443
HIGH RESOLUTION STUDY OF RYBBERG STATES OF BARIUM
E.R. Eliel and W. Hogervorst
Natuurkundig
Holland
Laboratorium,
Vrije
Univevs-iteit,
PB 7161 1081 HV
Amsterdam,
Résumé. - Nous avons étudié les séries 6snl, S, P, D et F de 1 atome de baryum avec
des lasers à colorant monomodes. La structure de la série F est analysée en tenant
compte des interactions électrostatiques, spin-orbite et hyperfine. On montre que
l'adjonction d'une interaction effective du type spin-orbite à 2 corps est nécessaire. La structure des niveaux de Rydberg est très sensible à la présence de niveaux perturbateurs ce que l'on démontre dans les séries S et F.
Abstract. - We have studied the 6snl S-, P~, D- and F-Rydbergseries of Barium
using CW dye lasers. The structure of the F-seri'es is analyzed in terms
of the
electrostatic repulsion between the two valence electrons, the spin-orbit interaction and the hyperfine interaction. However, an effective two-body
spin-orbit
interaction has to be included. The structure of the Rydbergstates is sensitive
to the presence of perturbing configurations, as shown in the S- and F-series.
We have performed a high resolution study
of the S-, P-, D- and F- Rydbergseries of the alkaline-earth element Barium. The
level structure reflects the
interaction between the two valence electrons outside closed shells. Configuration interaction with doubly excited states, which influence level positions',
Lande-factors and radiative properties ' , affect this structure as was recently
shown by Beigang et al.->>° for the D-series of Strontium and by Rinneberg et al.
for the S-series of Barium.
The even-parity Rydbergstates were populated by two-step excitation from the
ground state using two stabilized CW dye lasers. In our experimental set-up.which
is described elsewhere", the laserbeams perpendicularly intersect a
well-collimated atomic beam of natural Barium. The first laser is tuned to the
6s 2 1 S 0 •+
l
6s6p ~?i resonance transition at 553.5 nm and locked to individual hyperfine
or
isotopic components. The second laser then excites the atoms to the Rydbergstate.
Excitations take place in a field free region and the Rydbergatoms are detected
downstream using a field ionization detector. Absorption spectra are obtained by
scanning the second laser.
The odd-parity Rydbergseries were directly excited from the metastable 3 D j - and
3
D2-states at 9034 and 9216 cm
with our frequency-doubled CW ring dye laser.9
These states are efficiently populated in a discharge in front of the beam producing oven.
In this contribution we limit ourselves to a discussion
of some results obtained for the 1 S - and 3F-series.
The structure of the Rydbergstates is expected to be mainly determined
by
three interactions'^1, the electrostatic^repulsion
between the 6s- and nl 12
electron, the spin-orbit interaction £ i.s of the
n£-electron
and the
hyperfine contact interaction a I.s of the 6s-electron (only for the odd isotopes
135
Ba and 1 3 7 Ba with nuclear spin I = 3/2). These interactions are
diagrammatically shown in the upper part of Fig. 1. In a hydrogenic model it is
predicted that electrostatic repulsion and spin-orbit interaction scale as n*
,
where n* is the effective main quantum number. Since the Hyperfine interaction of
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982236
JOURNAL DE PHYSIQUE
1 -
the 6s-electron is constant, at higher
65
65
values of n* the
three interactions
- - - - :6;
}---o-;
have to be
treated
simultaneously.
A consequence of the decreasing elecf
trostatic repulsion and spin-orbit inel,,t,,,
,,,,
,,,,-,,
,,,
hyportlno
teraction is that the structure of the
65
odd-isotope Rydbergstates willtonverge
to the hyperfine
structure of the
2
ground-state of the Ba -ion. This
is
k=nll
illustrated in Fig. 2. In the up er
part a recording of the transition %l
+ 30f is shown. in the lower Dart
of
the transitionT3D1+50f. The -assign merit to the two
isotopes 1 3 5 , 1 3 7 ~ ~
FIG. 1 . DIAGRAMMATIC REPRESENTATION OF
and the single components of the even
THE INTERACTIONS.
isotopes 136'138~aare indicated. The
hyperfine and spin-orbit interaction in the odd isotopes strongly mix the '~3,
3~2,3,4-termsresulting in a complicated hyperfine spectrum. With increasing n a
doublet. Each
clear grouping appears at the high frequency side of the 136'138~a
group corresponds to a transition from a specific hyperfine level in 6s5d3Dl. The
residual structure within a group reflects the excited state sp$itting,decreasing
notably with increasing n and showing the convergence to the Ba - ground
state.
In Fig. 2 this grouping does not yet appear at the low-frequency side of
the
spectrum.
The analysis of the 6sns1s -series is
particularly simple due to thg absence of
spin-orbit-interactions. In Fig. 3
the
measured position of the odd i s o t ~ ~ e ~ ~ ~ B a
with respect to the
138~a-isotope is
plotted, showing an increasing separation
as a function of n, whereas the pure isotope shift is expected to become constant.
The observed effect is due to the hyperfine induced mixing of the two levels
with total angular momentum F = 312
longing to the
- and 3 ~ -1 termbg-,
expressed by the +nZn -zero matrixelement
i 1 ~ 0 , F = 3 / 2 1 a I . s 1 3 ~ 1 , F = 3 / 2 >With
.
increasing n thecsinglet-triplet separation decreases, resulting in a
stronger
repulsion between the two F= 312- levels.
A calculation along these lines,
using
known singlet-triplet splittings, results
in the smooth
curve
in Fig. 3. The
difference between experimental and calculated values in the interval n = 20-30
is constant and equals the isotope shift.
The irregularity at n = 18 is ascribed to
the perturber 5d7d1p0, as earlier observed
We observe theonset
by Rinneberg et al.
of a marked irregularity in the interval
n = 35 - 40, which is still under study.
The perturber is 5d7d3p1,which interacts
strongly with the 3~1-stateand thus via
the hyperfine interaction, also with the
+v
lsO-state.
The analysis of the F-series is more
FIG. 2. RECORDINGS OF THE TRANSITION
complicated. An
attempt
to fit
the
3 ~ +
1 nf
experimental spectra with the three afore
g: LASER GHOST.
mentioned interactions with corresponding
interaction constants (Slater
exchange
nd
O ~ I . C ~ ~ Y Ot w o - b o d y
.
.
S D I ~ I - ~ r b ,~tn t o r a c t m n
integral G3, spin-orbit coupling constant Snf
and
hyperfine constfnt a , assumed to be constant at the
value of the Ba -grognd state) was not succesful. For
40 good agreement it proved to be necessary to
include
n
an effective two-body spin-orbit interaction,diagrammatically shown in the lower part of Fig. 1, with
interaction constant a. This second order contribut30.
ion effectively accounts for the configuration interaction with all neighbouring Rydbergstates of
the
same series. With the three interaction constants G3,
25 a
Snf and a, shown as a function of n* in Fig. 4 in
log-log-plot, the experimental spectra were generally
20.
reproduced within 5-10 MHz. As can be seen from this
figure, where for convenience the functions n*-3 and
n*-4 (n* = n - 0.17) are also plotted, only for high
values of n* the limiting situation of the hydrogenic
Isotope shlft (GHZ C
is
Another interesting way of representing the resultsof
FIG. 3 . POSITION OF 1 3 7 ~ ~the F-series is given in Fig. 5. Here part of the
hyperfine level structure is shown as a function of n.
WITH RESPECT TO 13sBa IN
This figure is constructed in such a way that the F =
THE Gsns lSo-SERIES.
FULL
CURVE CALCULATED FROM lS0112-levels fall on a vertical line.
This hyperfine
3~ l
- ~ ~ ~ ~ ~ ~quantumnumber
l ~ ~ .occurs only in the 3~p-state,thus this
hyperfine level is unaffected by hyperfine interactions
levelswith 3~3,qand' ~ 3 . The F = 512, 712 and 912
which start in the lower left section of Fig. 5 cross repeatedly in the region
between n = 22 and 35 due to repulsions by nearby F = 512, 712 and 912-1evels.The
group of levels F=5/2-1112, which bend off at the right hand side of Fig.5 belong
to 3 ~ 4 ,the four levels at the top at the right of F = 112 belong to 3 ~ 3 while
the remaining levels are 3 ~ 2 .Not shown is the quartet
of
levels with
character. A marked irregularity appears around n = 20, again showing thepresence
of a perturber, probably of the type 5d8p3p2.
.
IF^-
Acknowledgement. - This work was financially supported by the Stichting voor Fundamenteel Onderzoek der Materie.
-+
Inn*
FIG. 4. THE INTERACTION CONSTANTS G ~ ,
Enf AND a AS A FUNCTION OF n* FOR THE
F-SERIES
.
FIG. 5. THE HYPERFINE STRUCTURE OF
F-STATES AS A FUNCTION OF n.
JOURNAL DE PHYSIQUE
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