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ABSORPTION AND POLARIZATION LABELING SPECTROSCOPY OF THE D1Πu-X1Σ+g
TRANSITION OF Na2
P. Niay, P. Bernage, H. Bocquet
To cite this version:
P. Niay, P. Bernage, H. Bocquet. ABSORPTION AND POLARIZATION LABELING SPEC-
TROSCOPY OF THE D1Πu-X1Σ+g TRANSITION OF Na2. Journal de Physique Colloques, 1987,
48 (C7), pp.C7-637-C7-642. �10.1051/jphyscol:19877154�. �jpa-00226976�
ABSORPTION AND POLARIZATION LABELING SPECTROSCOPY OF THE D ' ~ , - X ~ Z ~ TRANSITION OF Na,
P. NIAY, P. BERNAGE and H. BOCQUET
Laboratoire de Spectroscopic Moleculaire [CNRS UA-7791, Universite des Sciences et Techniques de Lille-Flandres- Artois, UFR de Physique Fondamentale, Blt. P5.
F-59655 Villeneuve-d'Ascq Cedex, France
A reanalysis of the absorption uv bands of Na2 i n the spectral range
(294 nm
-
325 nm) has been undertaken t o identify the infrared l a s e r emissions1 1
+
observed a t X 2 5.8 pm and 3.0 um when the D
nu
c X C system i s pumped by an 9XeCl l a s e r (A = 308 nm) [ 11
.
F i r s t , strong Q(J8') lines of the va = 0 + v" = 7 ,P 1
+
6, 5, 4, 3 bands were readily identified. Then, the very accurate X C s t a t e 9 molecular parameter s e t of KUSCH and HESSEL [ 21 enabled us t o recognize t h a t the previous rotational assignment f o r the v' = 0 vibrational level is too high by 2 (JAew = J i l d
-
2 ) [ 31.
One s t e p polarization labeling spectroscopy experiments following the scheme of figure 1 were then carried out t ounambiguously check the rotational numbering of other bands i d e n t i f i e d as corres- ponding t o v' = 4, 5, 6, 7, 8, 9, 10, 11 + v" = 0 transitions. The polarization labeling spectroscopy technique has been extensively described in t h e 1 i t e r a t u r e (see f o r instance reference t 41 and [ 51 ) : the method uses a narrow band pumping
v', J'
ONE STEP P O L A R I Z A T I O N L A B E L I N 6 S C H E M t
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19877154
C7-638 JOURNAL DE PHYSIQUE
l a s e r , polarized e i t h e r 1 inearl y or ci rcularly, which i s tuned t o resonance w i t h a molecular t r a n s i t i o n . I f a l i n e a r l y polarized broad-band probe l a s e r i s tuned near a molecular t r a n s i t i o n involving e i t h e r pumped 1 eve1
,
i t s polarization wi 11 be a l t e r e d only a t those frequencies resonant w i t h an allowed transition which shares a comnon level w i t h the pumped transition [ 4 ] . I f the probe beam i s passed throuah a crossed polarizer and then i n t o a spectrometer, these frequencies will appear as well-separated bright l i n e s . As a general r u l e , final rotational J numbers and final A angular momentum of the probe bright 1 ines can be determined i f the pumped t r a n s i t i o n i s assigned. Reciprocally, the rotational numbering of the s t a r t i n g level of an unidentified pumped t r a n s i t i o n can be assigned i f the probe signals a r e identified. We used t h i s property i n our experiment, owing t o the experimental impossibility t o tune an u v broad-band l a s e r t o the D 1 nu + x18+9 t r a n s i t i o n bands since they are located f a r below the lower limit of the spectral range covered by the currently available dye l a s e r s (340 nm < hdye < 1 000 nm).
According t o the analysis by TEETS e t a1 f 41
,
the signal intensity I on reso- nance condition i s given by relation (1) :in the lowest order approximation, where I. i s the probe l a s e r i n t e n s i t y
a, i s unsaturated absorption coefficient f o r the probe l i g h t , L i s the absorption length, AN/N i s the fractional change in the population of the lower level due t o pump l a s e r and 5 i s a dimensionless polarization factor. In Table I the large 3 values of the 5 f a c t o r calculated when the c i r c u l a r l y or l i n e a r l y polarized pump l a s e r i s tuned t o a It + XC t r a n s i t i o n a r e l i s t e d , while the probe l a s e r i s tuned t o a C + X Z t r a n s i t i o n . These values were obtained from Table I of r e f . [ 61 f o r a circularly polarized pump and from relation (15) of r e f . [5] f o r the l i n e a r polarization case [ 71
.
Thereby, we used a l i n e a r l y polarized pump l a s e r (1 51 + 6/10) instead of a c i r c u l a r l y polarized pump l a s e r (where 151 -t 0) in order t o obtain probe signals when pumping strong Q lines of the D 1nu
+ xlCt t r a n s i t i o n . The9
experimental scheme appears on figure 2. The pump l a s e r was obtained by doubling the frequency of a tunable v i s i b l e dye l a s e r through an angular phase-matched K.D.P.
f o r large J" rotational quantum number
PUMP clnu + x'ri
Circularly polarized pump
I
Linearly polarized pump O P T I C A L D E L A Y L I N EL A S E R
P U M P L A S I l
I
t - . € A M - S P L I T T T RO P l l C A L :TR
l , ~ ~ e , l
- - -
O P T I C A L f I L T E R
c r y s t a l . I t s frequency was tuned t o an unidentified D 1
nu
4 X'E' l i n e by monitoring1 9
the infrared emissions following the D
nu
s t a t e pumping. These emissions were detected by means of an InSb detector. A bright broad-band pump l a s e r l i n e a r l y polarized (oT) a t 45' with respect t o the pump beam was tuned to the spectral range of thellnU -
X'Z' t r a n s i t i o n v ' = 4, 5, 6 + v" =. 0 bands. The probe l a s e r , focused together 9with t h e pump beam i n the middle of a heat pipe oven (pressure = 2 Torr) t o a spot of nearly 1 mn radius, was delayed f o r about 20 ns from the pump pulse to ensure
1
+
t h a t the probe signal was connected t o the lower level ( X C, s t a t e ) of the Ll1IIu + X'Z' pumped t r a n s i t i o n .
a
9 -b -t
After a crossed polarizer (OP 1 OA) a coated f i l t e r removed the pump beam
C7-640 JOURNAL DE PHYSIQUE
and t h e probe beam was then sent through a 4 m f o c a l l e n g t h spectrograph. The probe spectrum and a comparison thorium spectrum were then photographed successively on a f i l m . The pump beam was then photographed on an another f i l m through t h e spectro- graph and i t s wavenumber o was measured w i t h 0.1 cm-I absolute accuracy against
P
t h e thorium spectrum. The probe s i g n a l s appeared as b r i g h t doublets together w i t h 1
+
some very weak s a t e l l i t e l i n e s . The A Pu s t a t e has been w e l l c h a r a c t e r i s e d [ 8 ] and i s known as being perturbed by a b 3 nu t r i p l e t s t a t e . Numerical d i a g o n a l i s a t i o n
of t h e energy m a t r i x given by C. EFFANTIN e t a1 [ 91 enabled us t o c a l c u l a t e
1
+
3 1+
wavenumbers f o r t h e A'P: + X P t r a n s i t i o n s and f o r t h e " s p i n forbiddenY b nu 4 X P
9 9
t r a n s i t i o n s when t a k i n g the m i x i n g o f the s t a t e s i n t o account. Thus, t h e s t r o n g doublets were r e a d i l y i d e n t i f i e d as corresponding t o P and R l i n e s o f the
1 + 1 +
A Pu + X P t r a n s i t i o n s , then p r o v i d i n g an unambiguous assignment f o r t h e a
9 P
wavenumbers
.
Some weak sate1 1 i t e 1 i nes a r e recognized e i t h e r as being c o l 1 i s i o n a l l y induced signals, o r s i g n a l s corresponding t o t h e b II,+ X i g + t r a n s i t i o n s , made v i s i b l e by the nearby s i n g l e t . These two kinds o f s i g n a l s have p r e v i o u s l y been observed [ 101.
Some s a t e l l i t e l i n e s remain u n i d e n t i f i e d and t h e question about t h e i r o r i g i n i s under i n v e s t i g a t i o n .The a n a l y s i s o f the data was made through a Dunham type expansion [ 21 given by equation (2) :
where u i s the wavenumber o f t h e l i n e , Yij are the Dunham parameters, 6 = -1 f o r the Q branch (J1-J1' = AJ = 0) and 6 = 0 f o r both the R branch (AJ = +1) and t h e
P branch (AJ = -1). I n the expression as w r i t t e n , (i , j ) cannot be (0,O). The Y i j c o e f f i c i e n t s were determined by making a least-squares f i t o f t h e observed l i n e wavenumbers and assigned quantum numbers t o equation (Z), t h e Y!' parameter s e t
l j
from r e f . [ 21 being introduced i n t h e f i t as a c o n s t r a i n t . The D 1 nu s t a t e molecular
Once t h e c o e f f i c i e n t s i n t h e Dunham expansion have been determined, one can apply t h e R.K.R. method t o o b t a i n t h e r o t a t i o n l e s s p o t e n t i a l curve f o r t h e D 1 IIu s t a t e . Using t h i s R.K.R. p o t e n t i a l curve and t h e one deduced from t h e para-
meters given i n r e f . [ 21 f o r t h e X'Z' s t a t e , we compute Franck-Condon f a c t o r s . 9
These Franck-Condon f a c t o r s , together w i t h t h e t r a n s i t i o n d i p o l e moment (assumed t o be a constant) are u s e f u l t o determine t h e i n t e n s i t i e s o f various absorption bands. A1 though no p r e c i s e i n t e n s i t y measurement has been performed, t h e r e doesn't appear t o be any obvious d l screpancy between t h e observed band r e l a t i v e i n t e n s i t i e s and t h e ones c a l c u l a t e d from Franck-Condon f a c t o r s . T h i s qua1 i t a t i ve agreement l e t us assume t h a t the previous v i b r a t i o n a l assignment o f t h e energy l e v e l s o f t h e
s t a t e i s c o r r e c t 131
.
TABLE I 1
-
Molecular parameters ( i n cm-' except f o r Re) f o r t h e Nap D 1 nu s t a t eY i j Calculated value Standard error
R E F E R E N C E S
[ 11 P. BERNAGE, P. NIAY, and H. BOCQUET, "Cascade l a s e r emission from t h e o p t i c a l l y pumped sodium dimer D 1
nu
s t a t e " , Tenth Colloquium an High Resolution Molecular Spectroscopy, Dijon, September 14th-
18th (11987).[21 P. KUSCH and M.M. HESSEL, 3 . Chem. Phys.
68,
2531-2606 (1978).C7-642 JOURNAL DE PHYSIQUE
C.V. WRIGHT, Ph. D. Thesis, Oxford U n i v e r s i t y (1960)
R. TEETS, R. FEINBERG, T.W. HANSCH, and A.L. SCHAWLOW, Phys. Rev. L e t t .
37,
11, 683-686 (1976).
N.W. CARLSON, A.J. TAYLOR, K.M. JONES, and A.L. SCHAWLOW, Phys. Rev. A
4
2, 822-834 (1981).
H. ITOH, M. HAYAKAWA, Y. FUKUDA, and M. MATSUOKA, Opt. Corn.
36,
131-133 (1981).The authors g r a t e f u l 1 y acknowledge Dr. N. W. CARLSON f o r p r o v i d i n g u s e f u l informations t o h e l p i n the c a l c u l a t i o n o f the 5 f a c t o r s .
M.E. KAMINSKY, J. Chem. Phys.
66,
4087-4088 (1977).C. EFFANTIN, 0. BABAKY, K. HUSSEIN, J. D'INCAN and R.F. BARROW, J. Phys. B
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