435
Journal of Fluorine Chemistry, 5 (1975) 435 _ 442 0 Elsevier Sequoia%A., Lausanne-Printedin theNetherlands
Received: October6.1974
PHOTOELECTRON
AND
VACUUM
ULTRAVIOLET
SPECTRA
OF
A
SERIES
OF
FLUOROETHERS
A.H.
HARDIN
and
Department
of
C.
SANDORFY
Chemistry,
University
of
Montreal,
P.Q.,
Canada
SUMMARY
FluOroethers
of the F(~F(cF~)cF~~)~cHFcF~
have their lowest
ionization
ordinary
Their ultraviolet
ethers.
at high frequencies, are complex
the existence
about 3.5 eV higher than
absorption
at about 80000 cm
indicating
cular orbitals
potentials
-1
(n = 1-4) type
spectra
or 10 ev.
of several
also begin
Both spectra
close lying mole-
in these compounds.
INTRODUCTION
The photoelectron ethers have been examined established molecules
and ultraviolet by several
that the lowest
the electronic
concentrated
transitions
and 120 nm also originate also been studied
authors
(1-8).
(first) ionization
is due to ejection
lone pair orbital
spectra
of an electron
of saturated It is well
potential
in these
from the essentially
around the owgen
atom and that
giving rise to the bands between in that orbital.
Fluoroparaffins
(7)(9) and it is known that the presence
200 have of the
l
436 fluorine
atoms causes large hypsochromic It seemed to us interesting
uv spectra. studies
on some fluoroethers
fluorines
shifts in both the PE and then to perform
in order to examine the effect of the
on the oxygen
lone pair orbitals
The following
compounds
F(CF(CF3)CF20)2CHFCF These exchangers
requiring
and high thermal
known under the designation we shall use these symbols
in general.
: CF3CF2C@2OCHFCF3,
were studied
are increasingly
and for applications
high resistivity
and the spectra
3, F(CF(CF3)CF,O)3CHFCF3
compounds
similar
and F(CF(CF3)CF,0)4CHFCF3. used in industry
low dielectric
and chemical
constant, They are
stability.
freon E-l, E-2, . . . etc.
as heat
For convenience
in this paper.
EXPERIMENTAL
The samples 3u Pont de Nemours purities
of fluorinated
and Company
rities
of Wilmington,
were checked by infrared
nance and gas chromatography. of greater
o.d. stainless
ethers were supplied by E.I.
absorption,
(30/60 mesh acid washed 'Krytox'.
on a 6 m (1.0 cm
with 33 % 'Kel-F' oil
column of chromosorb-GHP
and treated with dimethylchlorosilans)
Impurities
are mainly
reso-
found to have pu-
than 99.2 .wt. % when separated
steel) column of chromosorb-W
Sample
proton magnetic
The samples were
No. 3 or on a 3 m (0.5 cm o.d. copper)
55
Delaware.
residual
homologues
with
of this
ether family. One sample,%1, in order to verify
was further purified
the vacuum ultraviolet
tion of the E-2 and E-3 homologues than 99.9 %.
chromatographically
spectrum.
After
separa-
from E-l, its purity was greater
437
The photoelectron Elmer ~~-16 spectrometer using the oxygen 12.08, 15.59
spectra were recorded
Spectra were calibrated
with a He1 source. 12.32,
using a Perkin-
12,54 and 12.73 eV lines, the nitrogen Sample pressures
eV line, and argon 15.75 and 15.93 eV lines.
of 0.07-0.09 recorded
Torr
typically
(at the sample inlet) were used and spectra were with a counting
of 4 set and at 1 mm/min. vertical
Ionization
potentials
absorption
7 to 95000 cm-' were recorded chromator.
Radiation
from a hydrogen
grating before
beam sampling
attachment.
pair of EMI-6256-S tronics.
Details
UV absorption
passing
discharge
spectrum
is shown with molar
Some difficulty
-1
was encountered
for the photoelectron
to record&'jphotoelectron
a very low vapour pressure
material
with a
counting
elec-
The vacuum
extinction
coefficient
with a sample pressure
-1
A slit width
and 5nbelow
in stabilizing
work.
from>:-li.o1:-)1 in the order of increasing
model 665 double
was measured
LiF windows.
to 65000 cm
by a
(10,ll).
and was obtained
used from 95000 cm
was dispersed
to a McPherson
have been given previously
-1
model 225 lm mono-
tubes and photon
of 0.15 Torr in a 9.0 cm cell having
inlet pressure
in the range 50000 cm
Linear absorbance
photomultiplier
against wavenumber
of 2O~was
spectra
using a McPherson
1200 lines/mm
Attempts
quoted are for
transitions. The ultraviolet
plotted
rate of 4 x 103, a time constant
The problem boiling
65000 cm
.
the sample increased
point and viscosity.
spectra were unsuccessful appeared
-1
since
to form at the inlet port.
438 RESULTS
AND
DISCUSSION
The first peak in the PE spectrum The band
is broad,
however,
of E-l is at 13.9 eV.
with the onset at aLdut 12.6
eV
(Fig. 1).
'5t
E4
E3 E2 El
14 I6 ELECTRON
12 Fig. 1
18 VOLTS
The photoelectron
20
spectra
of F(CF(CF3)CF20)nCHFCF3
with
n = 1,2,3 or 4 (E-l, E-2, E-3, E-4).
Since the assignment
of this band is the most important
study we will discuss a much lower value.
For dimethylether,
ether and tetrahydrofuran 9.35
(0) is stabilized
towards
explaining
E-l and similar arises whether occupied
mainly
compounds.
populated
and 12.74
diethylether, values
orbital
Thus the oxygen
stability
lone pair or-
and very low associability
of
Since the 0 IP is that high the question
in the fluoroethers
the highest
in the C-C bonds;
n-C5Fl2
diisopropyl-
are at 9.94, 9.51,
that.is the hi&<-St
or not it is still am:$inly~otbital
molecular
n-C4F10,
ethers the first IP has
by about 3.5 eV, a fact that goes a long way
the chemical
In perfluoroparaffins
13.04
the vertical
(7) and 9.L6 eV (8) respectively.
bital
C3F8'
In saturated
it first.
point of this,
and n-C6F14
eV respectively
occupied
as it is in the ethers.
orbital
is known to be
the first IP for CF are 16.20,
according
14.48,
4' C2F6'
13.70,
13.30,
to the data of Robin and his
439 It is thus quite possible
coworkers
(7).
centered
at 13.9
to ionization
eV contains
from orbitals
ethers the second
1.6
ev.
oxygen
contributions of mainly
IP is widely
from one or more
having
from the first one, by about a large population
atom but less than for the highest potential
the fluoro-ethers. C-H bond might
A MO with a significant
of C-C character. energies).
population
follow at higher
from orbitals
of mixed
many fluorine
lone pair and bonding
side of the PE
more at higher
frequencies.
In saturated
to only one distinct The PE spectra
of E-l (Table I).
chain length,
at low
energies must originate with the
contributing
more and
such orbitals
none of the apparent
peaks
of ionization.
with changes
for the dimethyl,
due to increasing
diethyl
and diisopropyl
above.
We shall present the spectra
MO is
of the first band shifts by -0.42 eV in
This is consistent
such as observed
ethers mentioned
process
in
of E-2, E-3 and E-4 are very similar to that
The maximum
going from%I toE-4.
to intervene
molecules
Probably
have IP's above 15.5 eV.
corresponds
occupied
C-O, C-C, C-H, F and C-F character C-F orbitals
in
in the single
eV for CHF 3 (12)(13);
Thus the C-H is not expected
The PE bands which
This
frequencies
such as CH -CHF2 or CH3-CF (14) the highest 3 3
molecules
around the
orbital.
to the high energy IP is at 14.8
(The lowest
band at 13.9 eV.
usually
occupied
is likely to move to much higher
also contribute
IP's due
In nonfluorinated
C-C character.
separated
It is due to an orbital
ionization
yield
that the broad band for E-l
the ultraviolet
of our other compounds
no additional
information.
is at very high frequencies
are expected
of only E-l since
to be similar
The onset of UV absorption
(Fig. 2).
compounds
and to for E-l
This is in keeping with the
high first IP as well as with the spectra among the most translucent
spectrum
of fluoroparaffins
that exist.
The bands
which are in the
440 TABLE
1
Vertical
ionization
n = 1,2,3 and 4.
potentials
of F(CF(CF3)CF20)nCHFCF3
(E-l, E-2, E-3, E-4). n=2
i-l=1
with
ev
n = 11
n=3 eV
eV
eV
13.17 sh
12.76 sh
12.96 sh
13.89
13.77
13.78
13.47
14.90
14.87
14.87
14.96
16.17
16.18
16.20
16.22
16.82 sh
16.99 sh
16.90 sh
16.81 sh
17.51
17.56
17.49
17.53
20.48
20.21
20.33
20.12
6
\
5 -r "0 ;4 TE " -_ 3 @ G PI 2r
0I-_, 60,CCQ
\
I 70.000
90,000
80.000 CM-'
Fig. 2
The vacuum (E-l). ficients
ultraviolet
Wavenumbers
absorption
in cm
in liters mole
-1
spectrum
against molar
-1 cm-1
of CF3CF2CF20C extinction
coef
441 spectrum 84500
of E-l are broad.
and 87500
We find shoulders
CIII-~ and a band maximum
case of the photoelectron single electronic sitions
transition.
might contribute
broad bands
bands,
with centers
at 92000 cm
-1
.
near 81000,
Just as in the
none of these seems to be due to a
Both Rydberg
to the observed
and valence-shell
intensity.
do not enable us to make specific
tran-
The observed
assignments,
however.
CONCLUSIONS
The coincidence spectra
of several bands
leads to the frustating
individual
bands
situation
due to given transitions
certainty.
The main conclusion
the E-l,...
type have their lowest
13 eV, and that the highest close to each other. begin
in both the PE and UV that we cannot
identify
with any degree of
is that fluorinated
ethers of
IP's at very high values,
orbitals
Correspondingly
above
of 0 and C-C character the ultraviolet
must lie
spectra
also
at very high frequencies.
ACKNOWLEDGEMENTS
We acknowledge Research
Council
sociation.
financial
of Wilmington,
from the National
of Canada and from the Manufacturing
Our special thanks
C.S. Hoffman
assistence
Chemists
are due to Dr. R.L. McCarthy,
and Dr. R.B. Ward from the Du Pont de Nemours Delaware.
and Mr. R. Routhier
We are also indebted
from our laboratory.
As-
Dr.
Company
to Mr. P. Sauvageau
422 5.
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R. Demutu and J. Grobe,
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9.
S.
and M. K. Wilson,
G. Frankiss,
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Spectroscopy,
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10.
P. J. Hendra
11.
J. R. Allkins
12.
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