In an investigation of the Raman spectra of some ionized substances in aqueous solution, it was found [1] that the frequency shift given by a solution of potassium carbonate was in fairly close agreement with the strongest shift given by calcite. Data for such a comparison in other cases do not appear to exist, for change of frequency on scattering has been measured for only a few crystalline substances. In addition to calcite [2,3,5], these are quartz [2,3,4,5], ice [5], and topaz [6]. No modified frequencies were found in the light scattered by halite [2], NaCl, fluorite [5], CaF2, or by the salts [7] LiF and NaF. In the present paper are described the results of measurements on gypsum, CaSO4•2H20, and a comparison of these with data on ammonium sulfate solution

Dickinson, Roscoe G.

Dillon, Robert T.

English

Caltech Authors - Main

CHEMISTRY: DICKINSON AND DILLON
NOTE ON MR. KING'S PAPER: "THE CRYSTAL STRUCTURE
OF STRONTIUM"
By F. SIMON AND E. VOHSEN
DEPARTMENT OF CHZMISTRY, SYRACUSE UNIVERSITY
Communicated July 15, 1929
In No. 4 of this periodical King stated that on redetermining the crystal
structure of strontium he found a cubic face-centered lattice in agreement
with our measurements,' but that the unit cubic edge (as= 6.075 ='= 0.004
A.U.) was 0.7% greater than ours, which figured 6.03 A.U. King believes
that this rather considerable discrepancy is due to the fact that his measure-
ments, which were carried out with a view to obtaining very accurate
results, were more exact than ours. We feel bound to point out that this
is not the reason, but that our spacing applies to liquid air temperature-
a fact that King has apparently overlooked-whereas his value holds for
room temperature. The difference in question cannot be calculated
accurately but can be gauged at 0.03 A.U. 10% by the usual approxi-
mation as shown in our paper. Computed for room temperature our
result would thus be 6.06 A.U. The difference between this value and
King's is within the limits of our experimental error. We will not discuss
the question whether our value or King's is the more accurate, but we may
mention that in a recent paper Ebert2 gives the unit cubic edge of stron-
tium as 6.05 A.U. at room temperature.
I Zeit. phys. Chemie, 133, 165, 1928.
2 Zeit. anorg. Chemie, 179, 4, 1929.
THE RAMAN SPECTRUM OF GYPSUM
BY Roscon G. DICKINSON AND ROBERT T. DILLON
GATUS CHEMICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY
Communicated July 27, 1929
In an investigation of the Raman spectra of some ionized substances
in aqueous solution, it was found' that the frequency shift given by a
solution of potassium carbonate was in fairly close agreement with the
strongest shift given by calcite. Data for such a comparison in other
cases do not appear to exist, for change of frequency on scattering has
been measured for only a few crystalline substances. In addition to
calcite,23' these are quartz,234' ice,' and topaz.6 No modified fre-
quencies were found in the light scattered by halite,2 NaCl, fluorite,5
VOL. 15, 1929 695
CHEMISTRY: DICKINSON AND DILLON
CaF2, or by the salts7 LiF and NaF. In the present paper are described
the results of measurements on gypsum, CaSO4. 2H20, and a comparison
of these with data on ammonium sulfate solution.
The crystal used was a clear, colorless specimen internally free from
cleavage cracks. It was about 15 cm. long and had a cross-section of
about 2 cm.2; the long edges of the prism faces were parallel to the c-axis.
The crystal was placed in a water-jacketed glass tube with an end window
and irradiated with light from a mercury arc. The arc was placed parallel
TABLE 1
RAMAN SPUCTRA. FROM GYPsuM
PREQUSNCY OF
SHIFTED LINS,
CM. -1
24291.5
24085.0
24033.6
23985.7
23949.3
23896.1
23861.4
23798.1
23697.8
23569.3
23507.2
23351.5
22523.0
22445.2
22318.6
22267.3
21987.1
21929.9
21803.3
21303.2
21215.2
INTUNSITY Or WAVE LUNGTH OF
SHIFTSD LINH SXCITING LINE,A
Weak 4046.56
Very weak (broad) 4046.56
Very weak 4046.56
Medium (broad) 3650.15
Weak (broad) 3654.83
Strong (very broad) 3650.15
(3663.27)
Medium weak (broad) 3654.83
Medium weak (broad) 3663.27
Strong 4046.56
Medium 4046.56
Very weak 4077.8
Very faint 4358.34
Medium weak 4358.34
Very weak 4358.34
Weak (broad) 4358.34
Weak 4358.34
Very weak 4347.50
Very strong 4358.34
Medium strong 4358.34
Medium strong (broad) 4046.56
Strong (broad) 4046.56
FREQUENCY OF
EXCITING LINU,
CM. -1
24705.5
24705.5
24705.5
27388.4
27353.3
27388.4
(27290.5)
27353.3
27290.5
24705.5
24705.5
24516.1
22938.1
22938.1
22938.1
22938.1
22938.1
22995.3
22938.1
22938.1
24705.5
24705.5
FRUQUUNCY
CHANGH,
cm.-1
414.0
620.5
671.9
3402.7
3404.0
3492.3
(3394.4)
3491.9
3492.4
1007.7
1136.2
1008.9
-413.4
415.1
492.9
619.5
670.8
1008.2
1008.2
1134.8
3402.3
3490.3
to the c-axis of the crystal, and scattered light from the crystal was taken
off in the direction of the c-axis. Since the end of the crystal was quite
irregular, the crystal was submerged in chlorobenzene which has a refrac-
tive index close to those of gypsum. To insure that no scattered lines
had reached the spectrograph from the liquid, carbon tetrachloride,
which gives a quite different Raman spectrum from chlorobenzene, was
used in one case with no change in the observed scattered lines. The
glass tube containing the crystal was painted black around the ends of
the crystal. The light from the crystal was converged with lenses and
thrown on the spectrograph slit with the aid of a reflecting prism.
The spectrograph was a two-prism glass instrument arranged with
interchangeable camera lenses so as to give either a dispersion of about
PROC. N. A. S.696
CHEMISTRY: DICKINSON AND DILLON
100 cm.-I per mm. with an aperture of f 8, or a smaller dispersion and
higher speed corresponding to an aperture of f 3. A comparison spectrum
of the iron arc was recorded on each plate, and the plates measured on a
Gaertner comparator. The frequencies of the shifted lines were computed
by linear interpolation between the frequencies of closely neighboring
iron lines.
The measured frequencies and estimated intensities of the modified
lines are given in the first two columns of table 1. The wave-lengths and
frequencies of the corresponding exciting lines are given in the third and
fourth columns, respectively, while the frequency shifts are given in the
last column. As a control on the assignment of exciting lines to the
various observed lines, we have made a photograph while flowing through
the water-jacket an alkaline solution of potassium chromate of a con-
centration such that considerable light of wave-length X 4358 was trans-
GYPSUM
I. , 11 iil
(NHs25o4 SOLUTIO"
LAA~~~~~~~~~~~~Al , , I *0 1000 2000 3000
FIGURE 1
mitted, while that of shorter wave-length was largely absorbed. All of
the modified lines appearing on this photograph were ones for which
excitation by X4358 is indicated in table 1, and all lines thus indicated
appeared on the photograph with the exception of the very faint anti-
Stokes line.
The data of table 1 indicate eight different frequency shifts; the best
'values of these are summarized in table 2.
TABLE 2
FREQUZNCY SHIFTS GIVEN BY GYpsum
Frequency
shift (cm.-') 414.2 492.9 620.0 670.4 1008.2 1135.5 3403.0 3491.5
Intensity Med. Very Weak Weak Very Med. Med. Strong
weak weak (broad) strong strong strong (broad)
(broad)
We have also rephotographed the spectrum from ammonium sulfate
solution using higher dispersion than previously.' The new measurements
yield the following values for the frequency shifts of the Raman lines pre-
VOL. 15, 1929 697
CHEMISTRY: DICKINSON AND DILLON
viously reported: 451, medium (broad); 620, medium (broad); 980.3,
strong. In addition there appears to be a very broad shift with Av _.
1113 as well as the still broader band due to water with Av equal to about
3430. With this higher dispersion it is especially evident that the strong-
est line is far sharper than the others. A comparison of this spectrum
with that of gypsum is shown in figure 1.
The two largest frequency shifts given by gypsum are presumably due
to water of crystallization while the smaller shifts are very likely due
to sulfate ion. Schaefer and Schubert8 measured residual rays from a
variety of sulfates and concluded that all sulfates possess prominent
maxima of reflection in the neighborhood of 9 and 16Mi which are to be
attributed to the sulfate ion. In the case of gypsum, the maxima occurred
at 8.74 and 14.84/h with a weak maximum at 8.62/u, and another weak
one at about 3A due to water of crystallization. The two prominent
maxima correspond to frequencies of 1143 and 674 cm.-', respectively,
in reasonable agreement' with the values 1135.5 and 670.4 which we have
found. The two smallest Raman shifts do not fall in the range of the
residual ray measurements. The absence of any maximum corresponding
to the strongest Raman line (Av = 1008.2) suggests that the initial and
final states of the transition producing it are without electric moment,
as Carelli, Pringsheim and Rosen10 have suggested for an analogous line
in the case of calcite. This appears to afford a reasonable explanation
of the sharpness of this line in aqueous sulfate solution; for absence of
electric moment would presumably minimize the interaction between
sulfate ion and water molecules.
If the symmetry of the sulfate ion in aqueous solution may be taken as
tetrahedral, Brester's1' considerations concerning the multiplication of
characteristic frequencies consequent upon removal of symmetry afford
one possible explanation of the multiplicity of lines found from gypsum.
The point group symmetry of this crystal is monoclinic holohedral. The
space groups symmetry has been reported by Onorato12 to be C23h with
8CaSO4.2H20 in a unit of structure that employs a face-centered lattice;
if an end-centered lattice is used, the number of CaSO4.2H20 becomes
four. If the sulfur atoms occupy equivalent positions, the sulfate ion can,
strictly speaking, have only either a center of symmetry, a two-fold axis,
or a plane of symmetry in this crystal although it may approximate to a
higher symmetry. If the sulfur atoms are not all in equivalent positions,
a multiplication of lines could result for this reason. In any case, it is
also possible that the weaker Raman lines do not represent fundamental
frequencies.
1 Dickinson and Dillon, Proc. Nat. Acad. Sci., 15, 334 (1929).
2 R. W. Wood, Phil. Mag., 6, 729 (1928).
3 Gr. Landsberg and L. Mandelstam, Zeit. Phys., 50, 769 (1928).
698 PRoc. N. A. S.
VOL. 15, 1929 CHEMISTRY: DILLON AND DICKINSON
4 P. Pringsheim and B. Rosen, Zeit. Phys., 50, 741 (1928).
6 I. R. Rao, Indian J. Physics, 3, 123 (1928).
6 H. Nisi, Proc. Imp. Acad. of Japan, 5, 127 (1929).
7 C. Schaefer, Zeit. Phys., 54, 153 (1929).
8 Schaefer and Schubert, Ann. Phys., 50, 283 (1916).
9 This agreement may be fortuitous because of the fact that maxima of reflection
and absorption are not quite coincident and are sometimes very appreciably removed
from each other. See, for example, Havelock, Proc. Roy. Soc. 105A, 488 (1924).
10 Carelli, Pringsheim and Rosen, Zeit. Phys., 51, 511 (1928).
11 Brester, Ibid., 24, 324 (1924).
12 E. Onorato, Zeit. Krist., 66, 504 (1928).
RAMAN SPECTRA FROM ACETONE
By ROBERT T. DILLON AND Roscofi G. DICRINSON
GATGS CHZMICAL LABORATORY, CALIFORNIA INSTITUTS oF TerCHNOLOGY
Communicated August 1, 1929
Measurements of Raman spectra from acetone have been published in a
recent paper.' These measurements were so interpreted that out of
thirteen modified lines, twelve corresponded to frequencies of observed
infra-red absorptions, the thirteenth lying outside the range of the infra-
red measurements. This result is surprising; for the occurrence of fre-
quency shifts in Raman effect without the appearance of the corresponding
infra-red absorptions is a very common phenomenon. We have examined
Raman spectra from acetone; and as both our measurements and our
interpretation disagree with those mentioned above, it seems desirable to
report them.
The acetone used was Merck's "C.P." It was distilled through a 30 cm.-
Eastman fractionating column the product used all coming over within
0.050 of 55.70 at 746 mm. It is important to use materials of reasonable
purity; we have, for example, found it possible to bring out the strongest
benzene lines from a carbon tetrachloride solution containing only 0.46%
benzene.
The acetone was irradiated with light from a glass mercury arc, and the
spectra photographed with a glass spectrograph having a dispersion of about
100 cm.-' per mm. in the blue. The iron arc was used as a standard.
The measured frequencies of the shifted lines together with their in-
tensities are given in the second and third columns of table 1. Com-
parison of these measurements with those which have already been re-
ported' shows considerable disagreement even among the strongest lines.
Apparently seven lines are concerned in the production of these Raman
lines. The wave-lengths and frequencies of these mercury lines are:
699


The Raman Spectrum of Gypsum

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