Journal of Molecular Q Elsevier Scientific
INFRAREiJ
3l.J.D.
Structure,
PHOTOACOUSTIC
Low and
Department New York,
61 (1980)
119-124
119
Publishing Company, Amsterdam - Printed in The Netherlands
G.A.
SPECTROSCOPY OF SURFACES
Parodi
of Chemistry - New York N.Y. 10003 (U.S.A.)
University
-
4 Washington
Place
ABSTRACT photoacoustic,
A prototype coupled
with
scribed.
in
which
IR photoacoustic
several face
a reactor
computer-controlled
millimeters
sub-monolayer
spectra
thick
nodi fications
were
surface
corrosion
1 ayers.
and
were
species
of
may be treated samples
catalyst
carried
coverages
observing
samples
spectrometer,
and
on adsorbents,
have
new
been
an
to
beds
of
recorded of
technique
catalysts,
gases
of
IR absorptions The
observed.
with
consisting
pellets
out,
and
acoustic
1000°C.
and
, chars
and
dealumina
various
species
sur-
formed
is particularly
coals
is
silica
after
surface
cell
at
useful
carbons,
for
and
INTRODUCTIOll Infrared
spectroscopy
information
the
IR transmission
and
species are
present
and
study
range tial
structure
methods
so thick,
carbons, such
perhaps
that
have
of
the
been
and
such
single
molecular used
as commercial
we have
very
photoacoustic
the
effect
powerful
technique
bound
$0
extensively
There
are,
catalyst
methods
examined
most species
catalyst.
conventional
samples,
by means
the
of
on adsorbents
physically
chars to
about
is
fail.
it of
1,2),
and
of
the
so opaque, be useful
obtaining
data
describe
solids,
surface
some samples
or
would
obtaining
surfaces
studying
however,
feasibility (ref.
for
pellets, As
the
for
which such
as
to
be able
in
the
some of
our
IR ini -
results.
EXPERINEHTAL The atory
prototype 1 and
Figs.
operated
with
differential frequency
is shown
2.
The
signal
from
a l/2”
2804
power
supply
(ref.
chopper I/O The
spectrometer
a Type amp1 ifier
a generalized software.
IR-PAS
(ref. to
and 4), a Nova
monochromator
Model
124A
through
was
B&K Model 3)
lock-in
fitted
(ref.
A/D 6)
with
was
4165
led
amp1 ifier
a 15-bit
computer
schenatically
with
end-of-travel
largely
condenser
through
locked
converter
fitted
by the
a
(ref.
Model
a Model 5)
peripherals switches
microphone
P-A-R-C.
to
selfexplan-
192
variable
incorporated and and
IlC
suitable
a fiduciary
in
120
marker, and its continuous ble
by the
computer_
retained,
but
coating,
99.4%
thus
significantly
not
drive
The
additional reflective
in
the
analog
selected
:favelength
multiple
scanning,
ficult
and
range
were
so on.
dictated
by the
constant
the
LiF
-70
mm slits resp.).
was
Fig. As carrying device
shown
10)
prism
(0.50
the
tions
of
to
the
cock device
the and
region
then
lifted
worked
exploratory
of
Fig.
then
major
used
for
and
obvious
for
operating
were
available
2).
The
to
be 20,
mm slits),
and
and
the
in
and
is
expansions,
that
the
IR rather
more
than
dif-
the
The spectral
the
4 cm-’ 54
with
at and
the
spectra
ranges
slit
settings
2200
The -1 cm ,
with
CaF2
resolution.
38G0,
2300 and -1 36 cm , resp.,
frequency was 45 Hz and was chosen
ambient
reactions
3 was
requires
noise
spectrum
and,
The
constructed.
conditions. when
careful sample
Purified
the
pressures
had
was moved
the
microphone_
Turning
the
the
carriage
pressed
it
and
Its
objectionable
not
otherwise,
the
could
of
the
environment.
barrel against
steel
which
of
then
the
is
carriage
environment,
the
the
and
introduced
magnet
of
the
be degassed
equalized,
by an external
feature, is
control
he1 ium was
carriage
but
is
spectrometers
scale
the
along set
92,
The modulation in
spectrometer
beam, and digitize
difference
(ref. 9).
also
7.5
was
LH41
with
photoacoustic
ratioing,
which,
a scan),
treated
opera-
7) slits
The latter is a 2500°K carbon rod
source.
sample
we1 1 . work
is
(ref. the
in the form of a spectrum over pre-
detector
the
minimum
surface
device the
the
drive
between
Fig. 2.
gases under controlled opened,
a step
1.
out in
(ref.
throughout
(ref.
near
range
prisms
computed
this
micron
from Boyd et al .
was
because
3-25
suitable
latter
.‘jo,
mirrors
including
were
(-35,
All
The
(which
resp.,
kept
added.
of
adapted with minor modification covered
with
nonochromator
were
software
needed,
the
the sample with a "monochromatic"
and materials
are
replaced
of
from other single-beam
output
ranges;
technology
visible
the
different
filtered
was
path
mirrors
in that it will illuminate store
motor
original
large
Teflon
bottom
of
acceptable which
can
exposed
to
both
stopcock
through high the
for
the
the
the
introduce
sec-
was stopcock
vacuum celJ.
to
stopThe
present contam-
121
ination;
a quartz-enclosed
magnet
has
to
be substituted,
The sample
bed depth
was
- 2inm.
-2x3xl2
‘I
&
m
.(mgQAT
SPO%VELDED TO STEEL CARRIAGE MOVED BY EXtitiNkMAGNEf
-
TEFLON HLGNVACUUM STOPCOCK
Fig.
3.
Photoacoustic
The ordinates usually
recorded
2000 cl8 scan at
region
rate
the
are
high
a sample,
of
the
spectra
at
a rate
required
computing
units
.
the
being
were
used
, So,
at
the
were
under
double-beam
obtained
in
The range
spectra
charcoal
simu’iated
The spectra
prism
Ratioed
linear
wavelenght.
microns/step~se~.
15 min.
by the
of
are
O-00165
about
determined
S, and that
&own
of
wavenumbers.
then
spectra
and reactor.
cell
, so that covered
low
identical
by multiple
a scan
by the
instrumental
4000-
and
the
the
spectrum
conditions,
in
eight
scanning,
the
and by convenience
by recording
S/So , given
were
of
spectra
wavenumbers,
produced
spectrum
The spectra
arbitrary
of and
intensity
sequentially
recorded
added.
RESULTS Figs.
4 and 5 serve
af s , reagents,
materi surface
species
obtainable
are
of
2 mm deep sample caused
observed stretching
i?lustrate
the
and conditions
were
known
(refs.
by transmission-
The results
This
to
absorption
a sequence
band.
of
bed was first
a substantial
by the
decrease
11-14)
of
Llhen the
O-Ii
chosen
data
obtainable.
because
the
PAS data
The particular
surface
could
reactions
be compared
and with
others
methods. treatments
degassed
the
of
and the
surface
replacement
type
[A) of
band
and then
ESi-CJli and the
sample was exposed
of
to
silica
are
exposed
to
by %SI-O-SiHC72
shown CSiClS
in
Fig.
vapor
4. (B).
groups
formation
of
?IliS,
some Wi4C1 was formed
(C),
the
and can be -I 2260 cm Si -E
The
122
(Nk$
gives
halosilane
bands shifted
destroyed
these
numbers.
Treating
surface
rSi -OCH3
at
3130 the
surface the
and 3045
Si-H
species sample
4.
Surface
to
(II), with
and the 2239
and the methanol
coordination
cmW1 (ref. Si-Cl (E)
14).
stretch
then
caused
of
NH3 to
Degassing shifted the
to
the
surface
partially higher
formation
waveof
some
groups.
3900
Fig_
cm-l)
stretch
2100 cd
Modification
of
Silica.
3900
2100
123
ALUMINA DEGASSED
\/
AFTER /ESTERIFICATION
Fig.
5.
Surface
Similar ing
the
experiments spectrum
surface the
Al-O;1
sample
a band
Modification
had
in
the
these
being
prism
was
bands
were
were
(Fig.
groups
5)
of
used
in
not
to
to
order
to
with
alumina
showed
water
acetic
as well
attributable
out
alumina bound
exposed
region
Alumina,
carried
of
and
been C-H
of
and acid
as
a C-D
the
formation
obtain
data
broad
the
deformation
absorption
the
vapor, stretching of
below
After
(G!OM*/g).
the
band
O-H
and
band
ester,
2000
and,
cm-’
degass-
of
the
of
latter.
After
Hz0
bands declined, -1 1800 cm appeared,
near
a surface
a mild
characteristic
Al-OCOCHS.
The
unfortunately,
and
CaF2
the
C-H
resolved.
DISCUSSION It
is
about
apparent
surface
lets
(ref.
are
omitted;
most
of
tions,
15),
in
that
the
s.Si-OH
and
2260
a.
9 mono1 ayer.
to
detect
one
cm-l
will
above
which
were
Surface
treatments
amounts
bands of
Si-I-l
by the that
of
were
or
It
C,
is
For
relative
Fig.
was -1 cm
4,
2260
but,for
can
to
caused prior
peldata
note
that
to it
reac-
by molecular experience
intensities present
data
catalyst
chemisorption
were
band,
yield
brevity,
pertinent
example,
on the
the
solid
involved
species
less.
based
PAS method
included
earlier
some surface
of
IR
observed
elsewhere.
spectrum
intensity
amount.
the
examined
outlined of
species,
bands
that
species
a monolayer,
:Si-0-SiHC12
of
shown
be described
absorption
Judging tenth
solids
coal.
surface
the
present
indicates
and
results
various
examples
Other
glass
the
the
the
species.
so that
species
from
of the
should
the
extent
of
be possible
124 Some improvements resolution
will
improvement able
to
seem,
however,
examination ing
will
us has
and/or
of
in
be
instrumentation
required
for
be obtained dispersion
that
IR-PAS
the
leading technique
by employing
poor
physically
the
surfaces
a potentially
of
solids
scratched
are
sensitivity for
and
fogged
ancillary
opaque
because
and
research
monochronator;
useful
which
greater
be useful
a better
as we1 1 as
is
to to
the
only
prisms) IR
_
technique they
better
(an
are
immediate one
It
avail-
would for
highly
the absorb-
thick.
ACKNOWLEDGFMEIIT Support American
by grant Chemical
No. Society
3109-AC5 is
from
grateful
the ly
Petroleum
acknowl
Research
Fund
administered
by the
edged.
REFERENCES 1 2 3 4 5 6 7 3 9
10 11 12 13 14 15
A:. Rosencwaig, Opt. Commun. 7(1973)305. Y.-D. Pao, Optoacoustic Spectroscopy and Detection, Academic Press, N.Y., 3&K Instrument Co., Cleveland, Ohio. Princeton Applied Research Co., Princeton, N.J. Analogic Corp., Uakefield, Mass. Data General Corp., i1ew York, :i.Y. M.J.C. Low, in preparation. Laser Optics, Inc., Danbury, Conn. h’.T. Boyd, 3-E. Jennings, 1I.E. Glass, and M.N. Gailar, Rev. Sci. Instrum. 45( 1974)1236-1283. E.D. Pal ik and J.R. Stevenson, report AD $609902. L-h’. .Little, Infrared Spectra of Adsorbed Species, Academic Press, Xew York, 1966. A.V. Kiselev and V.I. Lygin, Infrared Spectra of Surface Compounds, John and Sons, Hew York, 1975. M.J.D. Low and ti. Hark, J. Catal. 44(1976)300-305. 1i.J.D. Low, A.G. Severdia and J. Chan, unpublished data. M.J.D. Low and G.A. Parodi, Spectrosc. Letters ll(8) (1978)581-588.
1977.
Cliley