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STUDY OF FINE STRUCTURES OF He+ AND Ne
BY BEAM-GAS SPECTROSCOPY
N. Billy, C. Lhuillier, J. Faroux
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C1, suppldment au
n o
2 , Tome 40, fdvrier 1979, page C1-20
STUDY OF FINE STRUCTURES OF ~ e + AND Ne PY BEAM-GAS SPECTROSCOPY
N. B i l l y , C. L h u i l l i e r and J.P. Faroux
L a b o r a t o i r e de Spectroscopic Vertzienne de lkE.N.S., 24 rue Lhomond, 75231 PARIS Cedex 05, France. Resume
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La technique des croisements de niveaux associ6e .3 une e x c i t a t i o n p a r j e t atovique a 6t.e u t i l i s e e :i ) oour l a d e t e r p i n a t i o n de 1 'ensevble 6e l a s t r u c t u r e en c h a ~ r nu1 du v u l t i p l e t n = 4 de He+. Ces determinations s o n t en bon accord avec l e s p r e v i s i o n s theo- r i q u e s .
i i ) pour l ' e t u d e des doublets 235nd&d( e t 2o5ndidY du Neon ( n = 3, 4 ) . Le conside- r a b l e p a i n de p r e c i s i o n dir i3 c e t t e technique nous a permis une etude f i n e de l ' e f f e t Zeeiran de ces niveaux. Des r e s u l t a t s i n a t t e n d u s a ~ p a r a i s s e n t dans l ' e t u d e de l a c o n f i n u r a t i o n 4d.
A b s t r a c t
-
Level c r o s s i n g resonances have been detected i n v a r i o u s gaseous t a r g e t s e x c i t e d by transverse bombardment. We here r e p o r t on two s e t s o f exoeriments :i ) on He+. From a whole s e t o f measurerents o f c r o s s i n g and a n t i c r o s s i n p resonances we have deduced t h e values o f a l l t h e f i n e s t r u c t u r e s p l i t t i n g s . A l l o u r r e s u l t s are i n good agreement w i t h t h e t h e o r e t i c a l p r e d i c t i o n s .
i i ) on Ne. Ue have achieved a p r e c i s e study o f t h e Zeenan e f f e c t o f t h e 2p5ndld&' atid 2p5ndidY l e v e l s ( n = 3, 4). The ~ e t h o d leads t o a n o t a b l e ~ a i n i n p r e c i s i o n i n t h e e x ~ e r i m e n t a l knowledpe o f these s t a t e s . Some unexpected r e s u l t s appear i n t h e Zeeman e f f e c t o f the 4d c o n f i v u r a t i o n .
INTPOPUCTION
here r e p o r t on l e v e l c r o s s i n g e x p e r i - The i n t e n s i t y ( o r p o l a r i z a t i o n ) o f the fluorescence r e n t s i n v o l v i n g : i ) t h e n=4 ~ u l t i p l e t o f He'; i i ) 1 in h t i s monitored i n two d i r e c t i o n s , p e r p e n d i c u l a r t h e d l e v e l s o f Neon. T h i s k i n d o f exoeriments on t o t h e m a r n e t i c f i e l d and r e s p e c t i v e l y a t 90° and one and two e l e c t r o n s atoms presents two c o n s t r a i n - 45' o f the beam a x i s .
i n n f e a t u r e s : f i r s t l y a l a r g e energy gap between The most severe l i n i t a t i o n o f such an t h e nround s t a t e and t h e f i r s t e x c i t e d s t a t e s and e x p e r i n e n t i s t h e weakness o f t h e a1 i gnment induced secondly l a r g e f i n e s t r u c t u r e s o f t h e order o f by c o l l i s i o n s . The p o l a r i z a t i o n r a t i o s o f t h e f l u o -
1 cm-l. The f i r s t c o n s t r a i n t e x p l a i n s why c o l l i s i o - rescence l i g h t are u s u a l l y r a t h e r weak (between n a l e x c i t a t i o n remains a p r i v i l e g e d t o o l t o e x c i t e
l o - *
t o and t h e l e v e l c r o s s i n n s i g n a l s appear t h e one and two e l e c t r o n s atoms * ) . The second one a g a i n s t a l a r ~ e backaround. I n o r d e r t o improve t h e favours l e v e l - c r o s s i n 7 ( o r a n t i - c r o s s i n g ) techniques s i g n a l - t o - n o i s e r a t i o , we use l o c k - i n d e t e c t i o n as compared t o time-resolved spectroscooy techniques. ( w i t h modulation e i t h e r o f t h e ~ a g n e t i c f i e l d , o r The l e v e l c r o s s i n ? aethod i n v o l v e s t h e use o f l a r o e o f t h e p o l a r i z a t i o n o f t h e fluorescence l i g h t ) . magnetic f i e l d s (up t o 20 kG f o r a 1 cm-I s t r u c t u - Each run, of t h e o r d e r o f a few v i n u t e s , i s accumu- r e ) , hence t h e absolute n e c e s s i t y o f a n e u t r a l beam l a t e d i n t o a s i g n a l averager u n t i l a s a t i s f a c t o r y f o r t h e c o l l i s i o n a l e x c i t a t i o n . s i g n a l - t o - n o i s e r a t i o i s obtained. During a l l t h e'Our experimental apparatus was described experiment, t h e magnetic f i e l d i s measured by a i n some previous references (1). An RF i o n source R.M.N. 5aussmeter which d r i v e s t h e signal-averager. produces an i o n i c beam (H+ o r He') which i s accele- A s p e c i a l care was devoted t o t h e s t a b i l i t y o f t h e r a t e d (between 30 and 50 keV), and then n e u t r a l i z e d beam; t h e
lone
tern; s t a b i l i t y i s o f t h e o r d e r of a by a charre exchange process i n a gaseous t a r g e t . few percent and we have achieved s h o r t term s t a b i - The n e u t r a l i z a t i o n e f f i c i e n c y i s between 60% and l i t y of the order o f upon a few minutes. For90%. Then t h e n e u t r a l beam e n t e r s t h e c o l l i s i o n a l t h e d i f f e r e n t r e s u l t s presented here t h e i n t e g r a - chamber p e r p e n d i c u l a r l y t o t h e h i g h magnetic f i e l d . t i o n t i m e v a r i e d from 1 hour ( f o r t h e f i r s t l e v e l -
...
* )
i t
i s l i k e l y t h a t within a feu yearsi t
w i l l be concurrenced by two photons spectroscopy and new U.V. lasers.c r o s s i n ~ s o f the 3d l e v e l s o f Neon) t o 10 hours ( f o r t h e r e s u l t s on He').
A . FINE STEUCTUZE OF THE n=4 *IULTIPLET OF t!e+ A n t i - c r o s s i n g s i g n a l s : t h e observa- I n t h e l a s t years, the f i n e s t r u c t u r e t i o n of a n t i - c r o s s i n g s i g n a l s i s a s p e c i a l f e a t u r e of ~ e ' (and most s p e c i a l l y o f t h e n=4 n u l t i p l e t ) o f hydronenoid species. b'e rrust renenber t h a t t h e has been t h e s u b j e c t o f many experimental studies; He+ i o n s a r e produced by c o l l i s i o n a l e x c i t a t i o n o f b u t these s t u d i e s have been mainly devoted t o t h e the atoms o f t h e t a r n e t ; i n such a process the p r o - measurement o f t h e L a ~ , b - s h i f t o f the J=1/2 l e v e l s j e c t i l e leaves a l i t t l e p a r t o f h i s momentum t o and o f t h e S%
-
PM s p l i t t i n g . i i l i t h t h e techniques t h e t a r g e t . So t h e ~ e ' io n s under study have a r e - described above, we have been a b l e t o deterpine the c o i l v e l o c i t y c f t h e o r d e r o f 4 kw/s; i n t h e l a r p e value o f a l l the f i n e s t r u c t u r e s p l i t t i n g s o f t h e magnetic f i e l d s we are considering, they experience c u l t i p l e t . By the study o f AL=@ l e v e l - c r o s s i n o s , we a motional e l e c t r i c f i e l d . Because o f t h e quasideqe were a b l e t o ~ a k e t h e f i r s t d i r e c t d e t e r m i n a t i o n o f neracy, i n hydrogenic spectra, o f l e v e l s o f d i f f e - t h e energy s p l i t t i n g s between same L l e v e l s , whereas r e n t p a r i t i e s , t h e induced S t a r k e f f e c t i s s u f f i - the study o f a n t i c r o s s i n g s and AL=2 l e v e l - c r o s s i n g s c i e n t t o mix p o p u l a t i o n s and coherences and t o allows us t o measure a l l the energy s p l i t t i n g s w i t h a l l o w the d e t e c t i o n o f a n t i c r o s s i n g s i g n a l s ( o f AL = 1, 2, 3. The whole c h a r a c t e r i s t i c s o f these f i r s t and h i g h e r o r d e r s ) .s i g n a l s have been s t u d i e d i n r e f . ( 2 ) ; we s h a l l here Results : we have measured t h e o o s i - b r i e f l y r e c a l l t h e i r ~ a i n f e a t u r e s . t i o n s of 8 c r o s s i n g s and a n t i c r o s s i n g s o f t h e
L e v e l - c r o s s i n n s i g n a l s : w i t h our geo- Zeeman diasram o f t h e n=4 w u l t i p l e t ( 2 ) . The corn- m e t r i c a l arrannerent, we c o u l d o n l y study two types p l e t e a n a l y s i s o f these r e s u l t s i n v o l v e s t h e study o f l e v e l - c r o s s i n g s : i ) AL=O, AHJ=2; i i ) AL=2, o f the r o t i o n a l Stark e f f e c t and t h e d e t e r m i n a t i o n AM,=O o r 3. The shape o f these s i p n a l s i s g e n e r a l l y o f t h e mean r e c o i l v e l o c i t y o f t h e i o n s ( 4 km/s); a m i x t u r e o f L o r e n t z i a n and d i s p e r s i o n curves ; i n i t leads t o t h e experimental values o f t h e f i n e t h e case o f AL=O crossings, i t s reduces t o the w e l l - s t r u c t u r e which a r e auoted i n Table I, t o g e t h e r known aspects ( L o r e n t z i a n f o r a d e t e c t i o n a t r i ~ h t w i t h t h e o r e t i c a l p r e d i c t i o n s and previous e x p e r i - angle w i t h t h e beam, pure d i s ~ e r s i o n f o r a d e t e c t i o n mental determinations.
a t 45' o f t h e bean).
TABLE I
E x ~ e r i m e n t a l and t h e o r e t i c a l values of t h e f i n e s t r u c t u r e o f ~ e + (n=4) ( i n MHz) t h i s work t h e o r e t i c a l r e s u l t s p r e v i o u s experimental
determinations
A t our knowledge, these r e s u l t s repre- B. -
NEON
c
1-22
JOURNAL DE PHYSIQUE of these c o n f i g u r a t i o n s r e s t on c l a s s i c a l o p t i c a l ~ ( d ; ) = 1.25*
'd4d4 = 1.778 cm-I s t u d i e s o f Paschen ( 8 ) and Green and People ( 9 ) ; g(d,) = 1.035
t h e p r e c i s i o n achieved i n these experiments was p(d;)
= 1.25
*
1one o r two orders o f maanitude lower than what can g(d;) = 0.9488 E ~ I ~ , , 1 1 = 1.7905 crr- be achieved w i t h l e v e l - c r o s s i n n techniques
.
Fromt h e t h e o r e t i c a l p o i n t o f view, Liberman's work ( l o ) The p r e c i s i o n o f these r e s u l t s i s o f t h e o r d e r o f p r o v i d e d us w i t h a r a t h e r good d e s c r i p t i o n o f t h e ; the p r e s e n t l i m i t a t i o n o f t h e p r e c i s i o n i s energy s p e c t r a of t h e d c o n f i g u r a t i o n s . From t h i s s o l e l y due t o t h e crudeness o f the t h e o r e t i c a l mo- study, i t appears t h a t t h e c o u p l i n g was very near d e l . ble can hope t o reach
a
p r e c i s i o n o f o r Racah's coupling. So we intended t o study t h e dou- b e t t e r w i t h t h e e x a c t parametric study o f t h e whole b l e t s o f s p i n l a b e l l e d dl,d, and did; i n Paschen c o n f i p u r a t i o n . A t t h i s staoe, we can conclude t h a t n o t a t i o n , which a r e i n Racah's c o u p l i n g ( j l , K; J) : Racah's c o u p l i n p i s a very good d e s c r i p t i o n o f t h e dl4 (3/2, 7/2; 4) d4 (3/2, 7/2; 3) 3d l e v e l s o f Neon.dol (3/2, 512; 3) d ' i (3/2, 512; 2) 2)
The Zeeman e f f e c t of these two doublets has been We have measured the f i v e f i r s t AM=2 s t u d i e d i n the n=3 and n=4 c o n f i a u r a t i o n s . l e v e l crossings o f t h e d4d4 s t r u c t u r e ( t h e s i x t h
1)
n=3
c o u l d n o t be measured because o f a poor s i g n a l t o Me have neasured t h e whole s e t o f AP:=2 n o i s e r a t i o ) , and the f o u r AE=2 l e v e l crossinas of l e v e l crossinqs ( 6 f o r t h e d o u b l e t d{d,; f o r t h ed o u b l e t d i d ? ) . Our r e s u l t s a r e shown on t a b l e 11.
Table I 1
P o s i t i o n s o f the AN=2 l e v e l crossings ( i n Gauss) 3d4, 3d4 s t r u c t u r e
experiment theor. f i t (see t e x t )
13245,6 13247,8 14621,7 14621,2 16170,9 16169,O 17901,4 17899,O 19818,3 19814,O 21905,l 21911,3 3 d i , 3dy s t r u c t u r e
experiment theor. (two l e v e l s sys tem) 14055,8 14054,8 16291,5 16293 ,O 18949,5 18950,5 22043,O 22041,4 t h e d r d i s t r u c t u r e . T h e i r p o s i t i o n s are shown i n Table 111. Table I11
P o s i t i o n s o f t h e AM=2 l e v e l crossings ( i n Gauss) 4d4, 4dt s t r u c t u r e exneriment t h e o r e t i c a l p r e v i s i o n s 8202,8 8189 9536,5 9019 11089,9 9951 12759,9 10990 14695 ,O 12138 4 d i , 4dy s t r u c t u r e experiment t h e o r e t i c a l p r e v i s i o n s
The s i g n a l t o n o i s e r a t i o was s u f f i c i e n t t o c l a i m I n t h e r i g h t column, we have w r i t t e n t h e r e s u l t s a p r e c i s i o n b e t t e r than 5 . 1 0 - ~ f o r t h e whole s e t o f a two l e v e l s c a l c u l a t i o n based on previous expe- o f measurements. For comparison, we have quoted r i m e n t a l knowledge o f t h e f i n e s t r u c t u r e (8) and
i n t h e r i g b t column o f Table
I1 t h e b e s t f i t f o r a
o f t h e Land& f a c t o r s ( 9 ) . There i s a l a r p e disagree- t w o - l e v e l s system. The mean square d e v i a t i o n b e t - ment between experimental and t h e o r e t i c a l values. ween experimental and c a l c u l a t e d p o s i t i o n s i s o f The f i r s t conclusion i s t h a t t h e Zeeman e f f e c t o f 3.5 G f o r t h e d4d4 s t r u c t u r e , and 1.5 6 f o r t h e t h i s s t r u c t u r e cannot be modelized by a two-levels d i d ? .his
s e t o f values leads t o t h e f o l l o w i n g system, hence t h e Racah's c o u p l i n g i s n o t a r e a l l y d e t e r m i n a t i o n of t h e z e r o - f i e l d enemy s p l i t t i n p s good d e s c r i p t i o n of these l e v e l s . We attempted t o and Land& f a c t o r s : have a b e t t e r d e s c r i p t i o n o f these l e v e l s by aparametric study o f t h e whole 4d c o n f i q u r a t i o n ; a t I n conclusion, we c o u l d emphasize t h a t t h i s time t h i s method f a i l e d t o ? i v e a r e a l impro- t h e l e v e l - c r o s s i n ? technique i s a very valuable me- vement. A f t e r a thorouah a n a l y s i s o f t h e e x p e r i - thod f o r p r e c i s i o n measurerents, and a l s o a most mental c o n d i t i o n s , we conclude t h a t t h e disagree- severe t e s t o f t h e o r e t i c a l d e s c r i p t i o n s b o t h o f ment between t h i s t h e o r y and experiments i s a r e a l t h e energy s p e c t r a and o f the wave-functions. one; i t remains a t t h i s stage unexplained. We p l a n
now t h e study o f r e l a t i v i s t i c e f f e c t s t o e x p l a i n these r e s u l t s .
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