Bromodifluoroacetyl fluoride, CF2BrC(O)F: Experimental and theoretical studies

Article abstract of DOI:10.1016/j.molstruc.2006.04.011

Bromodifluoroacetyl fluoride, CF₂BrC(O)F, was prepared through the gas-phase reaction of bromotrifluoroethene, CF₂CFBr, with molecular oxygen initiated either by NO₂ or CF₃OF. The compound was experimentally studied by FTIR spectroscopy of the gas phase and also isolated in Ar and N₂ matrices at low temperature. The energy differences between the possible conformers were theoretically studied, as well as the vibrational spectra of the conformers.

Full text of DOI:10.1016/j.molstruc.2006.04.011

Journal of Molecular Structure 825 (2006) 32–37
www.elsevier.com/locate/molstruc
Bromodifluoroacetyl fluoride, CF2BrC(O)F: Experimental
and theoretical studies
a
b
a,
*
Valeria B. Arce , Joanna Czarnowski , Rosana M. Romano
a
CEQUINOR (CONICET, UNLP) Departamento de Quı´mica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 y 115,
1900 La Plata, Argentina
b
Instituto de Investigaciones Fisicoquı´micas Teo´ricas y Aplicadas, INIFTA, Sucursal 4, Casilla de Correo 16, (1900) La Plata, Argentina
Received 23 March 2006; received in revised form 4 April 2006; accepted 4 April 2006
Available online 24 May 2006
Abstract
Bromodifluoroacetyl fluoride, CF2BrC(O)F, was prepared through the gas-phase reaction of bromotrifluoroethene, CF2CFBr, with
molecular oxygen initiated either by NO2 or CF3OF. The compound was experimentally studied by FTIR spectroscopy of the gas phase
and also isolated in Ar and N2 matrices at low temperature. The energy differences between the possible conformers were theoretically
studied, as well as the vibrational spectra of the conformers.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Conformational analysis; Matrix isolation; FTIR spectroscopy; Theoretical calculations; Bromodifluoroacetyl fluoride; Gas-phase reaction
1. Introduction
between the possible conformers and also to predict the
vibrational spectra of these conformers and thus help in
the correct assignment of the vibrational absorptions.
Several halodifluoroacetyl halides of the type
CF2XC(O)Y, with X, Y = halogen, have been subject of
conformational and vibrational studies during the last years.
CF2ClC(O)F [1], CF2ClC(O)Cl [2], and CF2BrC(O)Cl [3]
have been found to present predominantly the gauche con-
formation in equilibrium with the less stable anti conformer
(X atom oriented anti to Y atom). As far as we know, there is
no report in the literature about the bromodifluoroacetyl
fluoride, CF2BrC(O)F.
2. Experimental
The bromodifluoroacetyl fluoride, CF2BrC(O)F, was
produced as the main product of the thermal gas-phase oxi-
dation of bromotrifluoroethene, CF2CFBr, with molecular
oxygen initiated either by the addition of NO2 [4] or
CF3OF to the double bond of the alkene.
Here we present the preparation of bromodifluoroacetyl
fluoride, CF2BrC(O)F, through the gas-phase reaction of
bromotrifluoroethene, CF2CFBr, with molecular oxygen
initiated either by NO2 or CF3OF. The compound was
experimentally studied by FTIR spectroscopy of the gas
phase and also as isolated in an inert matrix environment
at low temperature. Theoretical calculations were per-
formed in order to determine the energy differences
All reactants were purchased commercially. NO was
eliminated from NO2 (Matheson 99.5%) by a series of
freeze–pump–thaw cycles in presence of O2 until disappear-
ance of the characteristic blue colour of N2O3. Finally, the
degassed NO2 was purified by fractional condensation
using the fraction that distilled between 213 and 243 K.
CF3OF (PCR, 97–98%) was washed with 0.1 mol dmꢀ3
NaOH and filtered at 80 K [5]. The CF2CFBr (PCR,
97–98%) contained CF4, and CF3CF3 as impurities. These
impurities are more volatile than CF2CFBr, but, as distill-
ing together could not be separated by fractional condensa-
tion. The CF2CFBr was purified by intermittent brief
*
Corresponding author.
E-mail address: romano@quimica.unlp.edu.ar (R.M. Romano).
0022-2860/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.04.011

V.B. Arce et al. / Journal of Molecular Structure 825 (2006) 32–37
33
evacuation cycles at 153 K, opening and closing the trap
valve. This procedure was repeated several times, until
the disappearance of the respective very strong absorption
CF2CFBr was consumed a slow pressure increase and the
formation of Br2 were observed.
The main reaction product was CF2BrC(O)F. Its yields,
based on the initial pressure of the alkene, increased from
79% to 85% as the pressure of NO2 decreased from 4.8 to
0.9 Torr. Minor quantities of C(O)F2 and C(O)FBr, and
small amounts of CF2BrCFBrO2NO2 and trifluorobromo-
O
bands of CF4 [6] and CF3CF3 [7] at 1279 and 1250 cmꢀ1
,
respectively, in the IR spectrum of CF2CFBr. Oxygen
´
(La Oxıgena 99.99%) was bubbled through 98% analyti-
cal-grade H2SO4 and passed slowly through a Pyrex coil
at 153 K.
ethene epoxide (TFBrEO),
CFBr, were also formed.
F2C
The experiments were performed in a grease-free con-
ventional static system, allowing pressure measurements
at constant volume and temperature. A spherical quartz
bulb of 270 cm [3] was used as reaction vessel. The pressure
was measured with a quartz spiral gauge.
Infrared spectra of the reaction mixtures were recorded
on Shimadzu IR-435 spectrometer. The gas and matrix-iso-
lated FTIR spectra of CF2BrC(O)F were recorded on a
Nexus Nicolet instrument equipped with either an MCTB
or a DTGS detector (for the ranges 4000–400 or 600–
200 cmꢀ1, respectively). The gas FTIR spectra were record-
ed at ambient temperature using 10 cm cell provided with
KBr windows with a 0.5 cmꢀ1 resolution.
Gas mixtures of CF2BrC(O)F with Ar and N2 (both
AGA) in the proportion ca. 1:1000, prepared by standard
manometric methods, were deposited on a CsI window
cooled to ca. 10 K by means of a Displex closed-cycle
refrigerator (SHI-APD Cryogenics, Model DE-202) using
the pulse deposition technique [8,9].
The compounds C(O)F2 [11] and C(O)FBr [12,13] were
identified by their respective IR spectra. The formation of
C(O)FBr was also detected by its UV spectrum in the range
of 200–220 nm [13]. The product CF2BrCFBrO2NO2 was
identified by its infrared absorption band at 1758 cmꢀ1
,
characteristic to the NO2 group of the haloalkylperoxyni-
trates and haloalkoxylperoxynitrate, appearing between
1754 and 1762 cmꢀ1. The trifluorobromoethene epoxide
(TFBrEO), was identified in the reaction mixture by its
infrared band at 1540 cmꢀ1, assigned to the ring-breathing
mode, that is characteristic of fluoroepoxides. This band
appears at 1500 cmꢀ1 for 1,1-dichloro-2,2-difluoroethene
epoxide [14], at 1550 cmꢀ1 for chlorotrifluoroethene epox-
ide [14] and at 1551 cmꢀ1 for perfluoropropene epoxide [15].
To obtain pure CF2BrC(O)F, the reaction mixture in the
reaction vessel was rapidly cooled to liquid air temperature
and the mixture separated by fractional condensation. The
fraction volatile between 158 and 183 K was CF2BrC(O)F.
The fractions of eight experiments were collected together
to obtain major amount of bromodifluoroacetyl fluoride.
Following deposition and IR analysis of the resulting
matrix, the sample was exposed to broad-band UV–visible
radiation (200 6 k 6 800 nm) from
a Spectra-Physics
Hg–Xe arc lamp operating at 1000 W. The output from the
lamp was limited by a water filter to absorb IR radiation
and so minimize any heating effects. The IR spectrum of
the matrix with a 0.125 cmꢀ1 resolution was then recorded
at different times of irradiation in order to monitor closely
any change in the spectra. The UV–visible spectra of the
products in the gas phase were recorded on a Hewlett–Pack-
ard Model 8452A spectrometer, using a 10 cm quartz cell.
All of the quantum chemical calculations were per-
formed using the Gaussian 98 [10] program system under
the Linda parallel execution environment using two cou-
pled PCs. Geometry optimizations were sought using stan-
dard gradient techniques by simultaneous relaxation of all
the geometrical parameters. The calculated vibrational
properties correspond in all cases to potential energy min-
ima for which no imaginary vibrational frequency was
found.
3.2. Gas-phase reaction between CF3OF, F2CFBr and O2
The experiments were made at 273, 253.5 and 239 K.
The initial pressure of CF3OF was varied between 0.9
and 2.4 Torr, that of CF2CFBr between 11.5 and 30.7 Torr
and that of O2 between 48.2 and 100.7 Torr.
At 273 K the reaction was completed in 10 min. At 253.5
and 239 K the time of permanence of the reaction system
CF3OF + CF2CFBr + O2 in the reaction vessel was
between 42 and 121 min. In all runs the CF2CFBr was
completely consumed.
The main product was CF2BrC(O)F (yields 81–95%
based on the CF2CFBr consumed). Minor quantities of
C(O)F2 and C(O)FBr, and traces of CF3OCF2C(O)F and
O
bromotrifluoroethene epoxide F C CFBr were also formed.
2
CF3OCF2C(O)F was identified by its IR spectrum [16].
The very strong absorption band of CF3OOCF3 at
1166 cmꢀ1 [17] and that at 1122–1119 cmꢀ1, characteristic
of CF3C(O)F [18], were not observed.
3. Preparation of bromodifluoroacetyl fluoride, CF2BrC(O)F
To determine the concentration of CF2BrC(O)F, the
room temperature infrared calibration curve was made,
allowing conversion of the absorption intensities at
1887 cmꢀ1 to the pressure of CF2BrC(O)F. The pressure
corresponding to the temperature of each run was calculat-
ed starting from the pressure of this compound at room
temperature obtained from the calibration curve.
3.1. Gas-phase reaction between NO2, CF2CFBr and O2
The experiments were made at 313.4 K. The initial pres-
sure of CF2CFBr was varied between 18.8 and 43.9 Torr,
that of NO2 between 0.9 and 4.8 Torr and that of O2
between 96.9 and 402.9 Torr. All experiments were carried
out to the complete consumption of alkene. After all

34
V.B. Arce et al. / Journal of Molecular Structure 825 (2006) 32–37
3.3. Mechanism postulated for the CF2BrC(O)F formation
4. Theoretical calculations
The CF2BrC(O)F is formed through a chain reac-
tion. The basic common chain reaction mechanism
for the oxidation of CF2CFBr, initiated by the addi-
tion of NO2 or CF3OF to the double bond of the
olefin in presence of O2, can be presumed to be as
follows:
A potential energy scan with the B3LYP/6-31 + G* the-
oretical approximation was performed along the Br–C–C–
F torsional angle of CF2BrC(O)F in order to localize the
structures that correspond to the energy minima. All the
geometrical parameters were simultaneously relaxed during
the calculations while the Br–C–C–F torsional angle was
varied in steps of 10ꢁ. The resulted potential energy curve
depicted in Fig. 1 shows three energy minima. Two of them
correspond to equivalent gauche structures with sBrCCF
equal to +80ꢁ and ꢀ80ꢁ, respectively. The third minimum
is localized for a torsional angle of 180ꢁ (anti conformer).
The syn form (Br atom syn with respect to F atom) consti-
tutes a maximum in the potential energy curve. The energy
of each form was then calculated with different approxima-
tions with the simultaneous relaxation of all the geometri-
cal parameters. The results, presented in Table 1, show that
the gauche conformer is the most stable one, according to
all the performed calculations. The theoretical proportions
of both forms were also obtained from the calculated free
energy difference, taking into account the multiplicity of
each conformer (mgauche = 2 and mtrans = 1).
Table 2 lists the geometrical parameters of the most sta-
ble gauche form of CF2BrC(O)F calculated with different
methods. Numbering in the table is in accordance with
the structure presented in Fig. 2.
The vibrational spectra of both forms of CF2BrC(O)F
were firstly calculated in order to characterize them as true
minima, for which no imaginary frequencies occur. The
wavenumbers of the gauche and trans conformers, together
with the IR relative absorption coefficient, are listed in
Table 3. From the calculated spectra of both forms we
can expect some differences in the spectra due to the
different conformers. For example m3, assigned to the
1. NO2 + CF2CFBr fi O2NCF2CFBrꢀ
2. CF3OF + CF2CFBr fi CF3CFBrꢀ + CF3Oꢀ
3. CF3Oꢀ + CF2CFBr fi CF3OCF2CFBrꢀ
ꢀ
ꢀ
4. O2NCF2CFBr þ O2 þ M ! O2NCF2CFBrO2 þ M
ꢀ
ꢀ
5. 2O2NCF2CFBrO2 ! 2O2NCF2CFBrO þ O2
ꢀ
ꢀ
6. CF3CFBr þ O2 þ M ! CF3CFBrO2 þ M
ꢀ
ꢀ
7. 2CF3CFBrO2 ! 2CF3CFBrO þ O2
ꢀ
ꢀ
8. CF3OCF2CFBr þO2þM ! CF3OCF2CFBrO2 þ M
ꢀ
ꢀ
9. 2CF3OCF2CFBrO2 ! 2CF3OCF2CFBrO þ O2
10. O2NCF2CFBrOꢀ fi O2NCF2C(O)F + Brꢀ
11. CF3CFBrOꢀ fi CF3C(O)F + Brꢀ
12. CF3OCF2CFBrOꢀ fi CF3OCF2C(O)F + Brꢀ
13. Brꢀ + CF2CFBr fi CF2BrCFBrꢀ
ꢀ
ꢀ
14. CF2BrCFBr þ O2 þ M ! CF2BrCFBrO2 þ M
ꢀ
ꢀ
15. 2CF2BrCFBrO2 ! 2CF2BrCFBrO þ O2
ꢀ
ꢀ
16. CF2BrCFBrO2 þCF2CFBr! CF2BrCFBrO2CF2CFBr
O
ꢀ
ꢀ
F C
CFBr
17. CF2BrCFBrO2CF2CFBr fi CF2BrCFBrO +
18. CF2BrCFBrOꢀ fi CF2BrC(O)F + Brꢀ
19. CF2BrCFBrOꢀ fi CF2Brꢀ + C(O)FBr
2
ꢀ
ꢀ
20. CF2Br þ O2 þ M ! CF2BrO2 þ M
ꢀ
ꢀ
21. 2CF2BrO2 ! 2CF2BrO þ O2
22. CF2BrOꢀ fi C(O)F2 + Brꢀ
The formation of traces of bromotrifluoroethene
epoxide indicates that small amounts of peroxy radi-
ꢀ
cals CF2BrCFBrO2 add to the double bond of
CF2CFBr, regenerating CF2BrCFBrOꢀ. The epoxidation
of alkenes by addition of peroxy radical RO2 to the
double bond, producing ROꢀ radical and epoxide,
was reported [19].
In presence of NO2 some peroxy radicals react through
the following reaction:
3
2
1
0
ꢀ
23. CF2BrCFBrO2 þ NO2 ! CF2BrCFBrO2NO2
After all the alkene has been consumed in the reaction
system NO2 + CF2CFBr + O2, the formed CF2BrCF-
BrO2NO2 decomposed slowly to give CF2BrC(O)F, Br2,
C(O)F2, C(O)FBr and NO2.
The lack of formation of CF3OOCF3 indicates that the
addition of CF3Oꢀ radicals to the double bond is consider-
ably faster than any other reaction of these radicals.
The respective formations of O2NCF2C(O)F and
CF3C(O)F in the corresponding reactions were not
detected, showing that, in comparison to the chain prod-
ucts, only very small amounts of these products were
formed.
-60
0
60
120
180
240
300
360
420
τ (BrCCF) [degrees]
Fig. 1. Potential energy curve for the internal rotation around the C–C
single bond of CF2BrC(O)F at the B3LYP/6-31 + G* level.

V.B. Arce et al. / Journal of Molecular Structure 825 (2006) 32–37
35
Table 1
Calculated energy, energy difference, free energy difference and proportion of the gauche and trans conformers of CF2BrC(O)F with different
approximation levelsa
Theoretical method
E gauche [hartrees]
E trans [hartrees]
DE [kcal molꢀ1
]
DG [kcal molꢀ1
]
% gauche
% trans
HF/6-31 + G*
B3LYP/6-31 + G*
ꢀ3018.787557
ꢀ3022.659941
ꢀ3018.783706
ꢀ3022.657073
2.42
1.80
1.65
1.46
97
96
3
4
a
mgauche = 2 and mtrans = 1.
Table 2
Table 3
˚
Calculated geometrical parameters (distances in A and angles in degrees)
Wavenumbers and IR relative absorption coefficients of the gauche and
anti forms of CF2BrC(O)F calculated with different approximation levels
of the gauche form of CF2BrC(O)F with different approximation levels
Geometrical
parameter
HF/6-31 + G*
B3LYP/6-31 + G*
MP2/6-31 + G*
HF/6-31 + G*
B3LYP/6-31 + G*
gauche
anti
gauche
anti
C1O
C2C1
BrC2
F2C2
F3C2
F1C1
C2C1O
BrC2C1
F2C2C1
F3C2C1
F1C1C2
F1C1O
F2C2C1O
F3C2C1O
BrC2C1O
BrC2C1F1
1.161
1.528
1.916
1.314
1.322
1.308
125.5
109.8
109.2
109.6
110.5
124.1
86.9
1.184
1.538
1.947
1.342
1.349
1.346
126.1
108.9
109.3
110.5
110.1
123.8
87.3
1.194
1.531
1.928
1.349
1.356
1.354
126.3
109.3
109.1
110.1
109.5
124.2
86.8
m1
m2
m3
m4
m5
m6
m7
m8
1934 (100)
1303 (37)
1224 (69)
1122 (85)
950 (53)
770 (6)
669 (31)
584 (8)
503 (2)
368 (<1)
324 (<1)
289 (<1)
238 (<1)
150 (<1)
60 (<1)
1934 (70)
1298 (78)
1173 (55)
1120 (30)
968 (100)
771 (9)
724 (21)
617 (6)
419 (<1)
332 (<1)
320 (1)
1935 (100)
1257 (46)
1176 (90)
1090 (98)
915 (62)
758 (5)
656 (30)
581 (10)
505 (3)
1940 (53)
1244 (70)
1115 (55)
1082 (22)
942 (100)
755 (6)
719 (15)
616 (4)
m9
417 (<1)
331 (<1)
319 (<1)
311 (<1)
244 (1)
m10
m11
m12
m13
m14
m15
370 (1)
319 (<1)
286 (<1)
239 (1)
150 (<1)
59 (<1)
309 (<1)
247 (2)
164 (<1)
43 (<1)
125.1
103.5
75.6
126.6
101.3
77.5
125.6
103.0
75.5
165 (<1)
32 (<1)
The assignment of the vibrational absorptions was made
F2
by the comparison with related molecules and also with the
results obtained from the theoretical calculations. The
descriptions of the modes presented here are only approx-
imate, being some of the vibrations mixed together. The
band occurring at 1887 cmꢀ1 in the gas CF2BrC(O)F is
readily assigned to the C@O vibrational stretching. An
overtone of this mode is observed at 3747 cmꢀ1. The
absorption at 1265 cmꢀ1 is assigned to the C–C stretching;
this value is very close to the 1275 cmꢀ1 reported for the
CF2ClC(O)F [1] related molecule. The antisymmetric and
symmetric stretching of the CF2 group is assigned to the
1195 and 1102 cmꢀ1, respectively. These modes appear at
1194 and 1107 cmꢀ1 in the IR spectrum of CF2ClC(O)F
[1]. The 937 cmꢀ1 band is attributable to the C–F stretching
mode, in comparison with the 970 cmꢀ1 absorption
assigned to the same vibrational mode in CF2ClC(O)F
[1]. The bands at 766 and 675 cmꢀ1 are assigned to the wag-
ging and deformation of the FCO group, also in accor-
dance with the 768 and 692 cmꢀ1 modes of CF2ClC(O)F
[1]. The deformation and rocking vibrations involving the
CF2 group are attributable to the 599 and 503 cmꢀ1
absorptions, that correlate very well with the 622 and
518 cmꢀ1 bands for CF2ClC(O)F [1].
O
C1
C2
Br
F3
F1
Fig. 2. Atom numbering for CF2BrC(O)F.
antisymmetric stretching vibration of the CF2 group, is pre-
dicted to shift between 50 and 60 cmꢀ1 to lower wavenum-
bers when the gauche form is transformed into the anti one.
5. Gas phase and matrix-isolated FTIR spectra
Table 4 lists the wavenumbers and relative intensities of
the FTIR absorptions of CF2BrC(O)F in the gas phase and
also as isolated in Ar and N2 matrices, in a proportion ca.
1:1000, together with a tentative assignment of the vibra-
tional modes. Comparing the experimental spectra with
those theoretically predicted, we can conclude that only
the gauche more stable form is present at ambient temper-
ature. Fig. 3 depicts the experimental FTIR spectrum of
the gas phase of CF2BrC(O)F (Pressure 10 Torr, 10 cm
path length, 0.5 cmꢀ1 resolution) and the IR spectrum sim-
ulated with the B3LYP/631 + G* approximation. The
agreement between the two spectra is very good.
There is no sign of the presence of the second conformer
either in FTIR spectrum of the gas phase or in the matrix-
isolated spectra. Moreover, the irradiation of the matrix
with UV–visible Broad-Band light, that is known to pro-

36
V.B. Arce et al. / Journal of Molecular Structure 825 (2006) 32–37
Table 4
Experimental IR wavenumbers and relative intensities of CF2BrC(O)F in gas phase and isolated in Ar and N2 matrices
Gas
Ar-matrix
N2-matrix
Assignment
3747 (<1)
3756.4 (<1)
3747.1 (<1)
2m (C@O)
9
9
1883:4
>
>
=
1884:3
=
1882:6
1880:8
1879:5
1887 (63)
ð88Þ
1883:4 ð75Þ
m (C@O)
>
>
;
;
1882:5
1265 (43)
1195 (90)
1267.4 (44)
ꢀ
1267.9 (100)
m (C–C)
ꢀ
1191:8
1191:5
ð88Þ
ð100Þ
mas (C–F2)
1191:2
1189:2
9
9
1102:9
1100:2
>
>
1100:6
1099:9
1099:6
1097:6
>
>
=
>
>
=
1102 (100)
ð86Þ
1099:1 ð75Þ
ms (C–F2)
>
>
;
>
>
1098:4
1097:4
>
>
;
9
=
9
=
980:8
980:4
980:4 ð8Þ
980:1 ð3Þ
?
;
;
979:8
979:3
9
933:3
>
>
=
ꢀ
932:6
931:6
931:2
932:9
ð53Þ
937 (63)
766 (3)
ð53Þ
m (C–F)
929:4
>
>
;
ꢀ
765:4
ð6Þ
765.1 (6)
FCO wag
764:7
9
ꢀ
663:8
=
662:3
662:0
675 (15)
599 (<1)
663:5 ð5Þ
ð20Þ
d (FCO)
d (CF2)
;
661:9
596.4 (<1)
596.2 (<1)
9
9
513:2
514:1
=
=
503 (1)
507:7 ð< 1Þ
513:8 ð< 1Þ
q (CF2)
;
;
507:4
509:4
6. Conclusions
A
The theoretical calculations predict the gauche form of
CF2BrC(O)F as the most stable one, with an energy differ-
ence ca. 2 kcal molꢀ1. This energy difference means that,
from a theoretical point of view, the most stable gauche
conformer contributes with more than 95% at ambient
temperature. This theoretical prediction was experimental-
ly confirmed since the gas phase and matrix-isolated FTIR
spectra of CF2BrC(O)F were fully explained through the
presence of the gauche form as the only one present in
the gas phase at ambient temperatures.
B
Acknowledgements
The authors thank Mr. Z. Czarnowski for helpful com-
ments. This work was supported by the Consejo Nacional
´
´
de Investigaciones Cientıficas y Tecnicas, CONICET.
´
R.M.R. thanks Fundacion Antorchas (14022-3), CONI-
Wavenumbers (cm-1
)
CET (PEI-6177) and Volkswagen Foundation (Professors
´
Oberhammer and Della Vedova grant) for the purchase
of the FTIR instrument.
Fig. 3. Comparison of the simulated IR spectrum for the gauche
conformer of CF2BrC(O)F using the B3LYP/6-31 + G* approximation
(A) with the gas phase FTIR spectrum (Pressure 10 Torr, 10 cm path
length, 0.5 cmꢀ1 resolution) (B).
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[20,21], had no effect on the features of the FTIR spectra.
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