Absorption-line series in Lu I

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Absorption-line series in Lu I

P. Camus, F.S. Tomkins

To cite this version:

P. Camus, F.S. Tomkins. Absorption-line series in Lu I. Journal de Physique, 1972, 33 (2-3), pp.197-

201. �10.1051/jphys:01972003302-3019700�. �jpa-00207239�

ABSORPTION-LINE SERIES IN Lu I (*)

P. CAMUS

Laboratoire Aimé

Cotton,

C. N. R. S.

II, 91, Orsay,

^France

and F. S. TOMKINS

Chemistry ^Division, Argonne

^National

Laboratory, Argonne,

^{Illinois 60439}

(Reçu

^{le 24}

septembre 1971)

Résumé. ²⁰¹⁴ Le spectre

d’absorption

^{de la} vapeur de lutécium dans la

région

ultraviolette a été

photographié

^en utilisant le

spectrographe

^de 9,15 ^m

d’Argonne

^{et un} four chauffé _par induction.

Deux cents raies ont été mesurées avec une

précision

^{de ±} 0,004

Å

et environ 91

%

d’entre elles ont été classées comme les membres de six séries de

Rydberg

^encore inobservées. Quatre ^{de ces séries} font intervenir des transitions provenant des deux niveaux fondamentaux 5 d

6 s2(2D3/2, 5/2)

^et

deux autres, des transitions ^avec le

premier multiplet

excité, ⁶ s2 6

p(2P01/2, 3/2), lequel

^{est suffisam-}

ment

peuplé

^{à la}

température

utilisée dans

l’expérience.

Une valeur de la

première

^limite d’ionisation de Lu I a été obtenue _par

extrapolation

de la série 5 d 6

s2(2D5/2)-nf

⁶

s2(2F07/2) qui, mesurée jusqu’à

n ⁼ 36, ^est

pratiquement

exempte de

perturbations.

^La valeur trouvée est de : 43 762,39 ± 0,10 ^cm-1 Abstract. ²⁰¹⁴ The

absorption

spectrum of lutetium vapor in the ultraviolet

region

^{has been}

photo- graphed, using

^the

Argonne thirty-foot spectrograph

^{and an}

inductively

heated furnace. Two hundred lines have been measured with an accuracy of ± 0.004

Å,

^and

approximately

⁹¹

%

^{of these}

have been classified as members of six

previously

unobserved

Rydberg

series. Four of these involve transitions from the two lowest

lying

levels, ^{5 d 6}

s2(2D3/2, 5/2),

^{and two} from the first excited multi- plet, ^{6 s2 6}

p(2P01/2, 3/2),

^{which is}

sufficiently populated

^{at the} temperature used in the

experiment.

A value for the first ionization limit of Lu I has been derived from the

extrapolation

of the serie 5 d 6

s2(2D5/2)-nf

⁶

s2(2F07/2),

^{which was measured to n =} 36 and wich is

pratically unperturbed.

The value found was 43 762.39 ± 0.10 cm-1.

Classification

Physics Abstracts : 13.20

Introduction. ^- The

absorption spectrum

^{of lute-} tium vapor has

previously

^been

investigated by Bovey

and Garton

[1 ],

^{but in a}

wavelength

range ^too restricted

(2 600 A-6 000 Â)

^to include the

singly

excited series nl 6

s2.

Klinkenberg [2]

^has

provided

^the

general

^frame-

work of the energy level

system

^{of Lu}

I,

^{but without} sufncicnt information about the

higher lying

^levels

to

permit

^a

good spectroscopic

determination of the ionization

potential.

More

recently,

the Zeeman effect measurements of

Pinnington [3]

have confirmed the identification of the terms

belonging

^{to the low}

lying multiplet

structures, but no

assignments

^{to more}

highly

^excited levels have been made. The presence of wide

hyperfine

^structure

complicates

^{the observed Zeeman}

patterns

^and

greatly

reduces their value in the classification of this

spectrum.

(*) ^{Based on work} performed ^{under the} auspices of the U. S.

Atomic Energy Commission.

Expérimental.

^{- The}

spectra

^{were obtained}

using

^a

modification of the

inductively

^heated furnace des- cribed

by

^{one of us}

[4], [5],

^{with a}

high-current hydro-

gen

discharge

^tube

[6]

^{as the}

background

^{source. The}

tantalum furnace

tube,

^which gave ^an

absorbing

column of

approximately

^five

^inches,

^was

operated

at a

temperature

^{of 2 200 °C and with a} helium gas pressure ^{of 2 torr to}

prevent rapid

^{diffusion of the}

sample

^{out of the furnace. With a} slit width of

35 kt,

a

good

continuum exposure in the third order of the

spectrograph required ^{twenty minutes,} using

^Kodak

S. W. R.

plates.

^The

reciprocal dispersion

^was

0.3

A/mm.

Wavelength

^{standards in} the second order were

recorded

using

^an electrodeless thorium

lamp,

^and

the

wavelengths

taken from the measurements of Giacchetti

[7].

^The

wavelengths

^{of the}

absorption

lines were determined

using

^the

Argonne

^semi-

automatic

comparator

^and

computer

^reduction pro- gram

previously

^described

[8].

Two exposures ^were taken and each measured twice. For the

sharp

^lines

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:01972003302-3019700

198

without

hyperfine

structure, the agreement among the several measurements was, ^on the average, 0.004

A.

Results and

Interprétation.

^{- Two hundred new}

absorption

lines of Lu 1 were

measured,

^{of which 185}

can be

assigned

^{to six}

Rydberg

^{series. The}

spectrum

between 2 280

A

and 2 480

À

is shown in

figure

^1.

The

positions

^{of the} identified terms ns

’S,

np

2po,

nd

2D

and nf

2Fo

are

plotted

^{on the Grotrian}

diagram

in

figure

^{2. Each term of an nl 6}

^S2

series is based on one or two observable transitions

starting

^{from the}

fundamental 5 d 6

s2(2D)

^{or from the first excited}

state 6 p 6

S2(2PO).

The series member of maximum n observed for the various nl

configurations

^{is indicated at} the upper left for each series in

figure

2. The maximum value of n increases with

increasing

^values of the orbital

quantum

number

1,

^and the transitions 5 d 6

s2(2D)-nf

⁶

S2(2pO),

labelled

Ai, A2

^{and B in}

figure 1,

^{are the}

strongest

observed in the

absorption spectrum.

^The

split-

ting energies

^{of each doublet term}

(excepting

^the

ns 6

S2 series) proportional

^to

(21

^{1 +}

1) ’nl/2 (where Çnl

is the

spin-orbit integral)

^decrease

gradually

^{to zero as}

n

increases,

^{and all} the observed series _converge to the

same limit which is the

ground state,

⁶

s2 IS0,

^of

Lu II.

The

quantum

^defect variation for each series was

fitted

using

the method

suggested by

^Seaton

[9]

^and

previously reported [10].

The members of the B

series,

^{i. e. 5 d 6}

S2(2D5/2)-

nf 6

S2(2 F70/2),

^{from n = 12 to n =}

^36,

^are

practically

free from

perturbation.

^The

plot

^of

quantum

^defect

versus reduced term value T for this series is shown in

figure 3,

and fits well the Ritz formula n - n * = a

+ bt,

with a ⁼

2.111 8,

^{b =} 0.864 9 and a value of 43 762.39 for the 6

S2(lS0)

limit. In these

calculations,

^{the rms} deviation in the term values was less than 0.04

cm-1

in each case, and we have

adopted

^{an estimated error}

of 0.10

cm - 1

for the

extrapolated

^{value of the limit.}

The

wavelenghts

and classifications of the lines are

FIG. l. ^- Rydberg ^{series 5 d 6 s2} 2D-np ^{6 s2 2PO and 5 d 6} s2 2D-nf 6 s2 2Fo in Lu I.

FIG. 2. ^- Grotrian diagram ^{of Lu 1.}

FIG. 3. ^- Quantum defects of the Rydberg series nl 6 s2 in Lu I.

given

^{in Tables I-VI.}

Using

^the

proposed limit,

^we have

assigned

^{an effective}

quantum

number for each term.

Looking

^{further at}

figure 3,

^{it is obvious that}

only

the terms of the 5 d 6

SI(2 D5/2)-nf

⁶

S2(2 F7/2) 0

^series

are free of

strong perturbations.

^{We can} say ^more

precisely

^{that for each term of the nf 6}

S2(2 FO)

^series

the

ZFS/2

^is

^strongly

^affected

^by

^a

perturbing

^level

which appears between the terms with n ⁼ 16 and

n ⁼

18,

^{indicated on}

figure

¹

by Pi.

^The

approxi-

mate

unperturbed position

^{of the term for n = 17}

is indicated

by

^{a dashed}

line,

^{which is the center of}

gravity

^of the lines marked

Pi

^and

P2.

The effect of this

perturbation

^{is more}

clearly

^{shown in}

figure 4,

where the

splitting energies

^{of the}

^2F

^are

plotted against

n for each observed term. The values for the doublet

intervals,

^{in each case}

taking

^the

position

^{of the}

2F7/2

^{term as zero, show an} inverted doublet for n bet-

ween 18 and 22. A similar effect has been observed in

CsI,

^{for the terms 4 f and 5 f}

[11].

^We have indicated

FIG. 4. ^- Splitting energy of the two levels 2F7/2 ^and 2F5/2 along the series nf 6 S2 2F° in Lu I.

TABLE 1

Lu 1 : 5 d 6

s2 2D-nf

6

s2 2F50/2 ^{series ;}

Limit : 43 762.39

cm-l

200

TABLE II

Lu 1 : 5 d 6

s2 2DS/2-nf 6 ^S2 2F 12 ^{series ;}

Limit : 43 762.39

cm-l

by

^{a dashed line the estimated}

position

of the unper- turbed doublet.

There are

strong perturbations

^{around n = 19 for}

the series 5 d 6

s2(2D)-np

⁶

s’(’P03/2),

^{and the}

pertur- bing

^{lines are marked}

p3

^and

P4

ⁱⁿ

figure

^{1. The lines}

PS

^and

p6

ⁱⁿ

figure

^{1 indicate that the}

corresponding

levels are

mixed,

^{and that their center of}

gravity

^{is at}

approximately

^the

expected position of 21 p 6 S2(2p/2)

level. All the

perturbing

levels have not

yet

^{been iden-}

tified,

^but

they

may well

belong

^{to the}

configuration 5 d 6 s 7 p, predicted

^to be around 41000

cm - 1 .

The

quantum

defect values _Iln for the different series are consistent. Table VII summarizes them for the terms with n ⁼

12, showing

^that Iln decreases as 1 increases and the

eccentricity

^{of the electron orbit}

becomes less.

Several of the

low-lying

^levels

assigned by

^Klinken-

berg [2]

^{have been}

reclassified,

^{and we have}

^summa-

rized these in Table VIII. The level marked with an

TABLE III

Lu I : 5 d 6

S2 2D3/2-np

⁶

^S2 2p/2 ^{series ;}

Limit : 43 762.39

cm-l

TABLE IV

Lu 1 : 5 d 6

s2 2D-np

⁶

^S2 Zp32 ^{series ;}

Limit : 43 762.39

cm-1

TABLE V

Lu 1 : 6

s2

6 _p

2P°-nd

6

s2 2D3/2 ^{series ;}

Limit : 43 762.39

cm - 1

TABLE VIII

of 5.41 ± 0.02 V

[13] ]

^{and 5.32} ± ^{0.05 V}

[14], by

surface ionization.

Conclusion. ^- The new

technique

^for

obtaining

TABLE VI

Lu 1: 6

s2 6

_p

2P°-6 s2

ns

2S 1/2 ^{series ;}

Limit : 43 762.39

cm - 1

TABLE VII

Quantum defect

^variation

for

⁶

^{s’ 12}

¹

asterisk is

assigned

^{J =}

3/2,

ⁱⁿ

spite

^{of the}

interpre-

tation

given by Pinnington [3] of

the Zeeman effect of the line at 3 376.50

A.

Our value of

3/2

^{is in}

agreement

with the

hyperfine

^structure

splitting

^observed

recently by

^Gôbel

[12]

^{in level}

crossing experiments.

Our value for the ionization energy,

expressed

^{in electron} volts is 5.425 7 ± 0.000 2. This is in

good agreement

^{with two}

previous

determinations

atomic

absorption spectra

^has

given

^a

precise

spec-

troscopic

value for the ionization

potential

^{of Lu 1}

and has added

significantly

^{to the}

description

^and

classification of the

spectrum.

References [1] ^BOVEY

(L.

^F.

H.)

and GARTON

(W.

^R.

S.),

^Proc.

Phys.

Soc., 1954, 67, 231.

[2] KLINKENBERG

(P.

^F.

A.), Physica, 1954, 21,

^53.

[3] PINNINGTON

(E. H.),

^{Can. J.}

Phys.,

1963, 41, ^1294.

[4]

^TOMKINS

(F. S.)

and ERCOLI

(B.), Appl. Optics, 1967,

6, 1299.

[5]

^TOMKINS

(F. S.)

and ERCOLI

(B.),

^J. Opt. ^Soc. Am.,

1969, 59, 1547.

[6]

^GARTON

(W.

^R.

S.)

^{and TOMKINS}

(F. S.), Astrophys.

J.,

1969, 158, 1219.

[7]

GIACCHETTI

(A.),

Argonne ^Nat.

Laboratory

Report,

n° A. N. L. 7209,1966.

[8]

^TOMKINS (F.

S.)

^{and FRED}

(M.), Appl. Optics,

1963, 2, 715.

[9]

^SEATON

(M. J.),

^Proc.

Phys.

Soc., 1966, 18, ^815.

[10]

^CAMUS

(P.)

and TOMKINS

(F. S.),

^J.

Physique, 1969,

30, 545.

[11]

MOORE-SITTERLY

(C.),

^Atomic

Energy

Levels, ^{Vol. III.}

[12]

^GÖBEL

(L. H.),

^Z.

Naturforsch. A,

1971, ²⁶ a, 1559.

[13]

^ALEKSEEV

(N. I.)

and KAMINSKI

(D. L.),

^Soviet

Phys.-

Techn.

Phys., 1965, 9, 1177.

[14]

^HERTEL

(G. R.),

^{J. Chem.}

Phys., 1968, 48, 2053.