Assuming first of all for simplicity that the four chlorine atoms are identical, the greatest symmetry the CCl
4
molecule could have is
T
d
. This would lead us to anticipate four fundamentals,
v
1
,
v
2
,
v
3
,
v
4
belonging to normal modes
A
1
,
E
,
F
2
,
F
2
, respectively, using Placzek’s (1934) nomenclature.
A
1
is the total symmetric normal mode, and so
v
1
is polarized in the Raman effect, and inactive in the infra-red.
A
1
is a singlet mode.
E
is a doublet mode and
v
2
is depolarized in the Raman effect, while it is inactive in the infra-red.
F
2
is a triplet mode and
v
3
and
v
4
are depolarized in the Raman effect and are also active in the infra-red. If the Raman spectrum of CCl
4
is examined under coarse dispersion, lines are observed at 217, 314, 459 cm.
-1
, identified as
v
2
,
v
4
and
v
1
respectively. Two at 760 and 790 cm.
-1
are usually regarded as the result of resonance degeneracy between
v
3
and (
v
1
+
v
4
), both in the mode
F
2
.
Fine structure of the Raman lines of carbon tetrachloride