Absorption of light in a solution of samarium nitrate

Physica

X, no 5

Mei 1943

ABSORPTION OF L I G H T IN A SOLUTION OF S A M A R I U M N I T R A T E b y P. F R A N Z E N , J. P. M. W O U D E N B E R G and C. J. G O R T E R C o m m u n i c a t i o n from the Z e e m a n - L a b o r a t o r i u m of the U n i v e r s i t y of A m s t e r d a m

Summary The intensities of the absorption bands in the visible region of an aquous samarium nitrate solution have been determined. In this laboratory a systematical investigation is carried out about the intensities of the absorption bands of rare earth solutions. One of us recently reported 1) about the intensities of the absorption bands in the visible region of aquous solutions of praseodymium chloride. We have extended the investigation to solutions of samarium nitrate. We used a Hilger constant deviation glass spectrograph belonging to the collection which has been placed at the disposal of this laboratory b y Prof. P. Z e e m a n. The only change in the method described in the previous paper was the use of the calibration *) of the tungsten bandlamp instead of a step-reducer for the determination of the density-intensity curve of the photographic plates. The solutions were prepared b y dissolving a weighed quantity of Sm2Q in nitric acid and adding water up to the desired volume. As usual the absorption is described b y the gram molecular extinction coefficient,

1

Io

k = -C--~ In T

where C indicates the concentration expressed in grammols per liter, d is the length of the light path and Io and I are the incident and the transmitted intensity of the light. *) The calibration has been carried out by the Physical La bora t ory a t U t r e c h t and we are indebted to Prof. M i I a t z for this courtcsy.

365

366

P. F R A N Z E N ,

J. P. M . v ~ r O U D E N B E R G

AND

C. ]. G O R T E R

"r

b0

O O

== =

O

o~ v

~o c~ .~ O ~

=<5

~) cO

-5c~ -- 0

•

C

ABSORPTION OF L I G H T IN A SAMARIUM SOLUTION

367

I n fig. 1 the value of k has been p l o t t e d as a function of the freq u e n c y between a b o u t 4500 a n d 8500 × l0 II sec -I (about 6400 A and 3600 A). The c o n c e n t r a t i o n C was 0.3 t h r o u g h o u t ; for the weak b a n d in the yellow and green spectral region a c o n c e n t r a t i o n C = 0.9 was used. In the investigation of the p r a s e o d y m i u m chloride it was found t h a t k did not d e p e n d on the value of C. In the present research this was not investigated systematically, t h o u g h a n y w a y the dependence of k on C is not considerable. P r a n d t 1 a n d S c h e i n e r have d e t e r m i n e d the wavelengths of the absorption m a x i m a in a solution of the chloride2). W i t h i n the limits of our a c c u r a c y these wavelengths generally agree with ourvalues. W e did not observe however separate bands with a m a x i m a at 4892 A (6130 X l0 II see -1) and 4 0 5 6 A (7390 x 10 tl sec -l) and did not resolve the b a n d at 4 1 6 5 A (7200 × 1011 sec -1) in three separate bands. On the o t h e r h a n d we descovered three weak bands in the yellow and green with m a x i m a at 5160 × 1011 sec -I (5810 A), 5660 × 1011 sec -I (5300 A) and 5730 × 1011 sec -I (5235 A). One could suspect t h a t these bands are due to a c o n t a m i n a t i o n with Nd. As the m a x i m a of the k n o w n absorption bands of a n e o d y m i u m solution do not quite agree however with the m a x i m a of our bands and as S p e d d i n g and B e a r 3) in their investigations on the absorption in crystallised SmCla.6H20 and o t h e r salts detected fairly strong absorption lines in the regions of our bands we are inclined to stick to the opinion t h a t the b a n d s are due to Sm. The n u m b e r of classical oscillators N per cm 3 in a solution of 1 g r a m mol per liter corresponding to an a b s o r p t i o n b a n d m a y be o b t a i n e d from the expressiori

cm fk(,~) dv N = --~e2! where c is the velocity of light and e and m the charge and mass of the electron. The n u m b e r of classical oscillators in one ion, which sometimes is called the p r o b a b i l i t y of absorption, is given bij P--

10aN 6.03 × 102a "

B o t h n u m b e r s are given in Table I for each of the bands. The total p r o b a b i l i t y of the absorption in the visible spectral region (down to 3 6 0 0 A ) i s 10.5 × 10-6 as c o m p a r e d to 19.55 × 10 -6

368 -

ABSORPTION OF LIGHT IN A SAMARIUM SOLUTION

i n Pr-solutions 1). In this respect it must be borne in mind however t h a t b o t h Sm and Pr ions h a v e strong absorption bands of a similar character in the near infrared 4) (about I ~) and t h a t Sm has also a few more absorption 'bands in the near ultraviolet. TABLE I Vmax X 10-xt

;kmm ~ X l0 s

5160 5330 5660 5730 6010 6250 6470 6640 6790 7200 7370 7460

(581o)

7680 8000 8280

N X 10 - 1 {

5593 (5300) (5235) 4995 4793 4639 4513

(4420)

(4165) 4074 4016 3905 3746 3620

0.26 0.22 0.07 0.03 0.37 7.6 4. l 0.142.0 5.5

P X 10a 4.3 3.6 I.I 0.5 6.1 126 68 2.3 33 91

29.6

490

1.8 6.4 5.4

30 105 90

N u m b e r of oscillators N and p r o b a b i l i t y of absorption P. The frequencies ot the m a x i m a derived from our curve have only a p p r o x i m a t e values. The wavel e ngt hs given in the second column are those given by P r a n d tl and S c h e i n e r 2) (in so far as t h e y have not been placed in parentheses).

We are indebted to Mr. T h. G. S c h o 1 t e, chem. cand., for his valuable assistance. Received March 5th, 1943.

REFERENCES 1) J . P . M . W o u d e n b e r g , P h y s i e a g , 217 and 936, 1942. 2) W. P r a n d t l und K. S c h e i n e r , Z. an. allg. Chemie, 220, 107, 1934. 3) F. S p e d d i n g u n d R . S. B e a r , Phys. Rex,.4Z, 5 8 a n d 7 6 , 1932; 44, 287, 1933; 46, 308 and 975, 1934. 4) H. G o b r e c b t , Ann. P h y s i k , . ° 8 , 6 7 3 , 1937. K 2597