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CHINESE JOURNAL OF PHYSICS
VOL. 25, NO. 4
WINTER 1987
Laser Raman Studies of Solid Carbon Tetrachloride
W. S. Tse (a 3 !&:)
Institute of Physics, Academia iinica, Taipei, Taiwan I1529
and
S. J. Lin (& $8 @Z)
Shu-Teh Junior College of Technology, Taichung 4020
(Received September 30, 1987)
The Raman spectra of crystalline carbon tetrachloride have been
recorded over the temperature range from 18K to the melting point of
250K. Changes in the molecular stretching spectra at various temperatures show that there are indeed three solid phases. The spectral
splittings are mainly due to crystal effects together with some isotopic
effects. The reorientational relaxation time of f. c. c., rhombohedral
and monoclinic phases are 1.25 psec, 1.4 psec, and 0.75 psec respectively.
1. 1NTRODUCTlON
At saturated vapour pressure, carbon tetrachlordie is known to exist in three solid
phaseslm4. In 1966 Rudman and Post’ reported that liquid carbon tetrachloride is frozen at
250.3K to a face-centered cubic phase (Ia). When crystals of this phase are maintained at
temperatures between 250.3 and 225SK they transform spontaneously, after several hours,
to a rhombohedral phase (Ib). Crystals of either the cubic or rhombohedral phase transform
to a monoclinic phase (II) below 225.5K. A return to higher temperatures induces a transformation back to the rhombohedral phase only. The cubic phase is plastic in nature with
the molecules rotating about their centres of mass. In the other two phases (Ib and II), the I
molecules are expected to be more highly ordered, but the exact structures are not known.
Crystal data and the direction of phase transition for the phases Ia, Ib and II are summarized
in table 1. Rudman and Post* apparently equated the three phases (f. c. c., rhombohedral
and monoclinic) with the CCL, I, Ccl, II and CCL, III as reported by Bridgman’ . However,
Piermarini4 reported that Ccl, III crystallizes in the monoclinic system with a unit cell of
the following dimensions:
a = 9.0798, b = 5.7648, c = 9.2018, P = 104.28 ” . The space group is P, I,c with four
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.
.
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LASER RAMAN STUDIES OF SOLID CARBON TETRACHLORIDE
Crystal data and direction of phase transition of Ccl,
TABLE 1
1 FACE-CENTERED CUBIC ;
a = 8.348,
II
z=4
I
I
LIQUID
MONOCLINIC
----.
1---------RHOMBOHEDRAL’
l
-qQ
‘3+1
a=20.3A,b= 11.6A
1
a = 14.4i%,cu=90.0”
\ z= 21
molecules per unit cell instead of the ordered monoclinic phase reported by Rudman and
Post2 .
In this work we have use the Raman method to study the phase transitions of solid
Ccl, occuring at saturate.d vapour pressure. Previous Raman studies are described in
refs.5 -‘.
11. EXPERIMENTAL TECHNIQUES
Raman spectra were obtained using a standard 90” scattering configuration. The light
source was a Spactra-Physics 165 argon ion laser operating at 0.4W on the 5 1458, line.
Scattered light was analyzed using a Spex 1401 double monochromator, coupled to a Spex
1442 third monochromator, and detected with an RCA 3 1034 photomultiplier, cooled by a
flow of nitrogen gas. The output pulses were then processed through an amplifier discriminator and then converted into an analog signal. The output analog signals were fed
into a Data General Nova 2/10 computer and subsequently displayed on a storage oscilloscope or X - Y plotter.
The cryostat used was an standard.modular liquid He dewar, Samples were obtained as
clear or translucent polycrystalline solids as the result of the slow cooling of liquid Ccl,
contained in the lower part of the tail section of the cryostat.
111. RESULTS AND DISCUSSION
Our discussion of the observed Raman spectra will follow the natural separation of
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W. S. TSE AND S. J. LIN
583
modes into stretching modes and lattice vibrational modes. Fig. 1 shows the Raman spectra
of the lattice modes of solid CCL, at various temperatures. Figs. 2 - 5 show the Raman
FREQUENCY <CG’)
Fig. 1
Raman spectra of solid CCL at various temperatures.
internal modes spectra of Ccl, in different phases at different temperatures.
In the free molecule of CCL, (Td symmetry), all four fundamentals v,. (A, ), vz (E), v3
(T?) and v4 (Tz ) are active in Raman scattering. In the monoclinic phase,‘a splitting of the
degenerate fundamental is expected to occur. The space groups of the face-centered cubic
phase and rhombohedral phase are not known definitely. Hence the interpretation of the
observed crystal splittings using factor-group analysis will be made only for the monochinic
phase using the structural analysis of Piermarini4 The group theoretical analysis” based on
P2 I,c unit cell group predicts two Raman components of the v1 (A, ) mode; four Raman
components of v2 (E); six Raman components of v3 (Tz ) and also six Raman components
of v4 (T2). In addition, there are also 12 non-coincident Raman lattice modes (6 translational and 6 librational).
We recorded the spectrum of the lattice modes at 240K (f. c. c. Phase) and kept the
sample at the same temperature for 3 hours and then recorded its spectrum again. Then we
lowered the temperature gradually to liquid helium temperature and recorded the spectra
again at different temperatures. The detailed temperature dependent lattice spectra are
shown in Figure 1. Since the structure of the crystal determines the shape of the lattice
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LASER RAMAN STUDIES OF SOLID CARBON TETRACHLORIDE
modes, it seems possible from the shape of the temperature dependent Raman spectra that
there are three different phases of Ccl,. A qualitativ,e explanation of the lattice spectra
related to those phases was presented in our previous paper’ so those details will not be
repeated here.
The u1 fundamental is a totally symmetric stretching mode and the spectra show the
several resolved peaks expected from the known isotopic abundance of C and Cl (see table
2). These peaks are independent of temperature and changes of state as shown in Figure 2.
TABLE 2 Isotopic abundance and relative intensities
Molecules
c35 Cl 4
.
P Cl, 37 Cl
c3* Cl, 37 Cl 2
c35 c137 Cl 3
c37 Cl 4
Abundance
32.54%
42.17%
20.50%
4.43%
0.36%
Relative Intensities
10.8 (34%)
12.0 (37%)
6.9 (2 1%)
2.5 ( 8%)
not obvious in spectrum
Vibrational Frequency
for Ccl, (cm-’ )
462.0
458.8 1
456.1
452.0
3.2
1 ;.;
1 .
The relative intensities agree resonably well with the five abundances of the five isotopic Ccl, molecules” given in table 2. The measured splittings vary from 2.7cm-’ to 4.1
cm- ’ . The calculated splittings are from 3.1 cm-’ to 3.3 cm-’ l2 . No factor-group splitting
is apparent for this assignment.
Fig. 2 Temperature dependent Raman spectra of u1 (Al ) mode.
W. S. TSE AND S. J. LIN
585
H. F. ShurvelP found that a deposite of CCL made at very low temperatures (liquid
helium) showed virtually no isotopic structure on the v1 band until the sample was warmed
up to the liquid nitrogen temperature. He assumed that the absence of the isotopic
structure indicated the existence of an amorphous form of Ccl, at very low temperatures.
However, there is no evidence for the existence of this amorphous phase in the present
work. In our work the isotopic splittings were still present at 28K. Shurvell used a deposited
film of CCL, as a sample so it is possible that the interaction between the sample and substrate introduced strains into the sample which smeared out the v1 band.
According to factor-group analysis the degeneracy of v2 (E) is removed at the site to
give a doublet. Further splittings would be due to factor splitting. The observed splittings
are shown in Figure 3. The v1 band ,consists of 4 peaks (217.3 cm-’ and 22.7 cm-’ are
shoulders). Ito13 observed only a single band for this fundamental. The four components
in this work must be due to both site and factor-group splitting.
I
11,
220
225
FREQUENCY (Cti’)
Fig. 3
Temperature dependent Raman spectra of v3 (Tz) mode.
For the v3 (TZ ) fundamental, according to G. W. Chantry’* , the calculated frequency
shift from C35 Cl, to C37 Cl, is only 2.0 cm-’ . However, as seen in Figure 4 the spectrum in
this region consists of six components, covering a frequency range of 38 cm-’ . It is obvious
that a very large factor-group splitting oqcurs in this case. Since this observation is in good
agreement with the prediction of factor-group analysis in which six bands are expected (3Ag
+ 3Bg). According to H. F. Shurvells there should be a Fermi resonance between v3 and vl
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LASER RAMAN STUDIES OF SOLID CARBON TETRACHLOdtDE
near vg region. However, J. H. Clark and B. K. Hunter14 reported that there is not any
Fermi resonance between v3 and v1 + v4. In this work it seems more likely that there is no
Fermi resonance between v3 and v1 + v4 since there is a very large factor-group splitting.
This is also in agreement with the prediction of six bands based upon factor-group analysis.
The spectra of the v3 mode at different temperatures shown in Figure 4, give itrong proof
that there are indeed three different phaseS of Ccl,. The ‘skdden changes in the spectra with
little change in temperature, particularly at the rhombohedral to monoclinic transition, are
indicative of the first order phase’transition.
+ v4
Fig. 4 Temperature dependent Raman’spectra of vi (Tz) mode.
v4 is triply degenerate and the site splitting should give rise,to,a triplet. The observation of two main features with a separation of about 3 cm-’ between components 317cm-’
and 3’20 cm-‘, as shown in Figure 5, together with a shoulder (3 13.2cm-’ ). on the low
frequency side is in good agreement with this prediction.’ However, the calculated isotopic
split-tin&’ in this case is 8.3cm-’ and the observed splitting in this work is founded to be
6cm-‘ . There is not much difference between these two values. Therefore the splittings
may be isotopic in nature.
The average time taken by a molecule in a solid (or liquid) to change direction from
one stable orientation to another is called the relaxation time. This time varies over a wide
range and is dependent on the temperature. In this work studies of the low frequency
region give us some information about the rotational motions of the Ccl, molecule in the
~
W. S. TSE AND S. J. LIN
I
310
,I,
310
587
315
FREOUENCY CCtii’~
Fig. 5 Temperature dependent Raman spectra of v4 (T2) mode
three phases. We used both the Debye theory and the Lorentz theory to find the iecorientational relaxation time but we find that a Debye function gives the better fit to our experimental data. The intensity using a Debye function is given by
I(w) = Aj+;:72
1 + ,’
eKT - 1
where 7 is the relaxation time, w is the frequency and A is a constant.
Thus, reorientational relaxation times were obtained by fitting the experimental data
to I(w). The relaxation times for the f. c. c. phase (240K), rhombohedral phase (240K) and
monoclinic phase (22310 are 1.25 X lo-” set, 1.4 X lo-l2 set and 0.75 X lo-l2 set
respectively. Figure 6 shows that the experimental results for the monoclinic phase at 240K
fit quite well with the theoretical Debye function with 7 = 1.25 X lo-‘* sec. There is
always some background due to the dark current from the photomultiplier and from stray
light entering the spectrometer. In, the cubic phase these two sources of background are
negligible, but stray light produces a large contribution in the other phases. It is the
problem of separating out a background spectrum that made it impossible to obtain times
which are accurate enough to clearly distinguish the phases f&m each other.
As_:
.
‘
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LASER RAMAN STUDIES OF SOLID CARBON TETRACHLORIDE
588
---Experimental
I
11
30
.O
*o
result
80
FREQUENCY (Cm’1
Fig. 6
The Rayleight wing and
Debye tit for the monoclinic phase at 240 K.
IV. CONCLUSIONS
The Raman spectra and reorientational relaxation time fitting of polycrystalline Ccl,
reported here is generally good in confirming the existence of three phases of CC& (la, Ib
and II). The group theoretical analysis based on a monoclinic system with four molecules
per unit cell seems to apply reasonably well to the spectra at 28K. The spectral splittings
are mainly due to crystal effects together with some isotopic effects. In this work only
polycrystalline samples were examined and hence most of the bands were broad and unpolarized. Obviously more unambiguous results could be obtained using single crystals of
the three phases but it may be impossible to obtain such samples due to the cracking at the
first order phase transitions.
REFERENCES
1.
2.
3.
4.
5.
P. W. Bridgman, Phys. Rev. 3, 153 (1914).
R. Rudman and B. Post, Science 154, 1009 (1966).
C. E. Weir, G. J. Piermarini and S. Block, J. Chem. Phys. 50,2089 (1969).
G. J. Piermarini and A. B. Braun, J. Chem. Phys. 58, 1974 (1973).
H. F. Shurvell, Spectrachem. Acta, 27A, 2375 (1971).
W. S. TSE AND S. J. LIN
589
6. B. P. Nevzorov and A. V. Sechkarev, Soviet Phys. J. 14, 199 (1971).
7. I. I. Kondilenko, P. A. Korotkov, and G. S. Litvinov. Opt. Spectry 30, 5 1 (197 1).
8. Y. Ebisuzaki, Proceeding of the International Conference on Lattice Dynamics, Paris,
505 (1977).
9; A. Anderson, B. H. Torrie and W. S. Tse, Chem. Phys. Letters, 61, 119 (1979).
10. W. S. Tse, C. C. Chen, H. Chang and N. T. Liang, J. Raman Spectry 15, 5 1 (1984).
11. S. Sunden and R. E. D. Mclung. Chem. Phys. 2,467 (1973).
12. G. W. Chantry, Spectrachem. Acta. 21, 1007 (1965).
13. M. Ito, Spectrachem. Acta, 27,73 1 (1965).
14. J. H. Clark and B. K. Hunter, J. Chem. Sot. (A), 299 (197 1).