High-Resolution Infrared Study of the Fundamental Bands of Deuteroiodoacetylene

Article abstract of DOI:10.1006/jmsp.1997.7376

The high-resolution infrared spectrum of deuterated iodoacetylene has been measured in the region 200-2700 cm^-1. In addition to all five fundamentals, the bands 2v₄⁰ and 2v₅⁰ have been identified. The measurements were carried out by using a Fourier transform spectrometer at room temperature with instrumental resolution of about 0.0020 cm^-1. The ground state rotational constants B₀ = 0.0970742961 (72) cm^-1, D₀ = 1.38482(20) × 10^-8 cm^-1, and H₀ = -1.47(10) × 10^-15 cm^-1 have been determined by combining 462 ground state combination differences from the same bands mentioned above with accurate MW data from the literature. In addition, the molecular constants for all the fundamental levels have been obtained.

Full text of DOI:10.1006/jmsp.1997.7376

JOURNAL OF MOLECULAR SPECTROSCOPY 185, 15–20 (1997)
ARTICLE NO. MS977376
High-Resolution Infrared Study of the Fundamental Bands
of Deuteroiodoacetylene
H. Sarkkinen, A.-M. Tolonen, and S. Alanko
Department of Physical Sciences, University of Oulu, P.O. Box 333 Linnanmaa, FIN-90571 Oulu, Finland
Received December 26, 1996; in revised form June 13, 1997
The high-resolution infrared spectrum of deuterated iodoacetylene has been measured in the region 200–2700 cm01
.
In addition to all five fundamentals, the bands 2n04 and 2n05 have been identified. The measurements were carried out
by using a Fourier transform spectrometer at room temperature with instrumental resolution of about 0.0020 cm01 . The
ground state rotational constants B0
Å
0.0970742961(72) cm01 , D0
Å
1.38482(20)
1
1008 cm01 , and H0 Å 01.47(10)
1
10015 cm01 have been determined by combining 462 ground state combination differences from the same bands
mentioned above with accurate MW data from the literature. In addition, the molecular constants for all the fundamental
levels have been obtained.
᭧
1997 Academic Press
I. INTRODUCTION
II. EXPERIMENTAL DETAILS
The deuterated monoiodoacetylene sample was produced
in our laboratory using the method of Brown and Tyler
(7). In the process, in hypoiodite solution, the hydrogen of
acetylene is replaced by iodine. At first, we made the weakly
alkaline hypoiodite solution by adding iodine to potassium
hydroxide. To obtain the other exchange reaction, too, the
solution was prepared in deuterium oxide instead of normal
water. Then acetylene was bubbled slowly through this solu-
tion and diiodoacetylene sedimented as a main product of
the reaction. Deuteromonoiodoacetylene gas was collected
Deuterated monoiodoacetylene, DCCI, is a linear mole-
cule with five fundamental vibrations, three stretching
modes of S/ symmetry (C–D stretch at 2600 cm01 , C–
C stretch at 1930 cm01 , and C–I stretch at 530 cm01 ),
and two bending modes of
P symmetry (C–C–I bend at
250 cm01 and C–C–D bend at 490 cm01 ). The IR studies
of the DCCI molecule are almost entirely missing. Only
the n1 band has previously been observed in our labora-
tory (1). The dipole moment of the molecule is very small
and so there are problems when applying the microwave
technics. Only recently the first observations have been
made. Heineking and co-workers (2–4) have observed
in a trap at a temperature of
0
75ЊC and then distilled into
the sample cell. The sample includes small amounts of acety-
lene and water as impurity, which can be seen in the spec-
trum. The spectrum shows that the species HCCI is present
in the sample, too.
two rotational transitions J
Å
1
R
0 and J
Å
3 R 2
including eight and three hyperfine components, respec-
tively. The accurate B and D rotational constants for the
ground state have been reported (2).
The measurements were performed with a Bruker IFS 120
HR FTIR spectrometer in Oulu. The components used in
different spectral regions together with further experimental
details are given in Table 1. All the measurements were
performed at room temperature. The overview spectra of the
fundamental bands are shown in Fig. 1 and a small part of
the spectrum around the n5 Q branch in Fig. 2 illustrates the
spectral overlap in the low wavenumber region. The spectra
of the five fundamentals were measured in three different
The series of high-resolution infrared studies on the
normal isotopic species of iodoacetylene has been going
on in our laboratory during the past years (5, 6). As a
natural continuation, we have started the measurements
on the spectrum of deuterated species, DCCI. The present
work reports the analysis of the fundamental bands of
this molecule. Ground state rotational constants and mo-
lecular constants for all the fundamental levels have been
obtained with high precision. In addition to the funda-
mentals, the 2n40 and 2n05 bands have been measured and
applied in the ground state analysis. Our purpose is to
continue the present studies with analyses of the numer-
ous hot bands observed in the measured spectra and fur-
regions. The lowest one includes n3 , n4 ,
n5 , and 2n05 bands
between 230–550 cm01 . The highest stretching, n1 at 2600
cm01 , and the weakest of the fundamentals, n2 at 1930 cm01 ,
were measured separately. In addition to the fundamentals
and 2n05 , the rather strong overtone band 2n04 at 1000 cm01
ther to determine the harmonic force field of the HCCI was measured. In the calibration of the n1 ,
n2 , and 2n04 region
molecule, in general.
spectra, the accurate N2O and OCS lines were used (8–10).
15
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16
SARKKINEN, TOLONEN, AND ALANKO
TABLE 1
Experimental Details of the Measurements of DCCI
The calibration of the crowded lower region spectra (n3
,
n4
,
obtained from each observed band separately. The fits
n5 , and 2n05 ) was performed with 42 water lines (11) ob- agree well with each other, and because the standard devi-
served in the spectrum as impurity.
ations of the separate fits are nearly equal, the differences
of all the bands were put into the same final IR fit with
equal weights. The results are seen in the upper part of
Table 3. The constant H is not well determined in the
separate fits but the statistical accuracy is clearly im-
proved in the combined IR analysis. The present values
are in good agreement with the results of MW analysis
(2) shown in Table 3, too.
The next step was to add the rotational transitions from
Ref. (2) to the fit. Since the rotational lines exhibit hyperfine
structure, the unsplit line positions were first calculated using
the same hyperfine model and constants as in Ref. (2). Then
III. ANALYSIS AND RESULTS
1. Ground State Constants
In the assignment work the Loomis–Wood program (12)
was used. The number of assigned lines with the highest
observed J values are shown in Table 2. As a first step
of the analysis the ground state rotational constants were
determined. The differences
(J
upper state, were first calculated. Then the polynomial
d
(J,
D
J
Å
2)
Å
nR (J)
0
nP
/
2) between the observed P and R lines, with the same
for these corrected lines Eq. [1] was used with
Estimated from the standard deviations, 1.2 kHz (Ref. (2))
and 4.7
1005 cm01 (Table 3), the relative weights of 106
D
J
Å
1.
d
(J,
D
J)
D0[(J
H0[(J
Å
/
B0[(J
J)2 (J
J)3 (J
/
D
J)(J
/
/
J
D
J
/
0
1)
J2 (J
J3 (J
0
J(J
1)2 ]
1)3 ],
/
1)]
1
0
D
/
D
J
1)2
/
[1]
were given to the rotational lines.
The obtained constants with some statistical information
from both the separate and final fits are seen in Table 3.
The values obtained seem to be reasonable when compared
/
/
D
/
D
/
1)3
0
/
where
D
J
Å
2 in the case of IR data, was fitted to these
differences. The ground state rotational constants were with those of HCCI, which are listed at the end of Table 3.
Copyright ᭧ 1997 by Academ ic Press

FUNDAMENTAL BANDS OF DCCI
17
FIG. 1. Overview spectra of the fundamental bands of DCCI. Experimental conditions are given in Table 1. Note the transmittance scale in the case
of the very weak n2 band. The P branch of the n3 band is seen just under the Q branch at 520 cm01 and the R branch is the weak series above 530
cm01 . A strong Fermi resonance mixes the upper states of the bands 2n50 and n3 badly. The assignments given here are based on the mixing ratios
obtained from the preliminary analysis of this resonance.
2. Upper State Constants
of a bending fundamental with
are obtained by substituting l Å {1 and by using an auxiliary
term 1)]J(J 1) resulting from the l
12[qt qJt J(J
doubling. Equation [2] is applied for the ground state with
G£ , , and l set to zero.
In the analysis of the bands, the ground state constants
were constrained according to the values from the final
fit (DCCI) given in Table 3. The summary of the experi-
mental data with the range of rotational levels is given
in Table 2 and the results from the fits are collected in
P symmetry, the term values
In each vibrational level, the unperturbed vibration–rota-
tion term values are the diagonal elements of the conven-
tional energy matrix. For a linear molecule they are ex-
pressed as
{
/
/
/
£
T£,l,J
Å
G£
/
B£[J(J
/
1)
0
l2 ]
l2 ]2
[2]
0
D£[J(J
/
1)
0
/
H£[J(J
/
1)
0
l2 ]3 .
For a stretching mode with S/ symmetry the term values Table 4. Furthermore, by using the results from Tables
are calculated from this expression with l
Å
0. In the case 3 and 4, the rotational constants B£ and the centrifugal
Copyright ᭧ 1997 by Academ ic Press

18
SARKKINEN, TOLONEN, AND ALANKO
FIG. 2. Part of the spectrum in the region of the n5 Q branch to illustrate the density of the spectra. The bending CCI is very low in wavenumbers
and so many hot bands starting from the level £5 Å 1 and from its overtones can be seen in the spectra.
distortion constants D£ and H£ have been calculated and with J
listed in Table 5.
£
5 in all the bands from the analysis. Another
reason for rather large line omission, see Table 2, is the
growdiness of the spectra. Especially in low wavenumber
region, see Figures 1 and 2, lots of lines were extracted.
Furthermore, in the case of n1 band there seems to be a
IV. DISCUSSION
Mainly because of the large quadrupole moment and
spin of iodine nucleus, the two-nuclei (D and I) hyperfine
splittings are quite conspicuous in the DCCI molecule;
see again the rotational transitions in Ref. (2). The effects
are so large that they can be seen in the low J infrared
lines, too. These lines appear slightly broadened and are,
unfortunately in our point of view, clearly shifted from
their unperturbed positions. Our model did not include
local resonance. The P and R lines up to J
Å
15 are
symmetrically shifted and had to be left out from the
analyses, while in the calculation of combination differ-
ences they could be used.
When comparing the resulting constants for the upper
levels of the fundamentals in Table 4, it can be noticed that
the constants for the n3 band are anomalous. As known from
the corresponding investigation on HCCI (5, 6), the level
the hyperfine effects and so we had to exclude the lines £3 Å 1 is strongly coupled to the overtone level £5 Å
2
TABLE 2
Number of Assigned Lines Together with the Number of Lines Actually Used
in the Analyses of the Upper States of DCCI
Copyright ᭧ 1997 by Academ ic Press

FUNDAMENTAL BANDS OF DCCI
19
TABLE 3
Ground State Constants (in cm01 ) of DCCI
by Fermi resonance. There exists also an l-type resonance mental n3 . To obtain the unperturbed molecular constants
for the fundamental level £3 Å 1, the hot bands 2n50,{2
0
between the
S
(l5
Å
0) and
D
(l5 Å {2) states at the
n15 and n3
0
n15 appearing in the n5 region must be simultane-
overtone level £5 Å 2. So, these coupled energy levels cannot
be analyzed only by using the overtone 2n05 and the funda- ously analyzed.
TABLE 4
Results from the Analyses of the Fundamental Bands of DCCI (in cm01
)
Copyright ᭧ 1997 by Academ ic Press

20
SARKKINEN, TOLONEN, AND ALANKO
TABLE 5
Calculated Rotational Constants (in cm01 ) of the Fundamental Levels of DCCI
5. A.-M. Tolonen, S. Alanko, M. Koivusaari, R. Paso, and V.-M. Horne-
ACKNOWLEDGMENT
man, J. Mol. Spectrosc. 165, 249–254 (1994).
6. A.-M. Tolonen, S. Alanko, R. Paso, and V.-M. Horneman, Mol. Phys.
83, 1233–1242 (1994).
7. J. K. Brown, and J. K. Tyler, Proc. Chem. Soc. (London), 13–14
(1961).
The authors thank Professor Rauno Anttila for valuable discussion and
for his comments on the manuscript.
8. G. Guelachvili, and K. Narahari Rao, ‘‘Handbook of Infrared Standards
with Spectral Maps and Transition Assignments between 3
2600 m.’’ Academic Press, San Diego, 1986.
mm and
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Copyright ᭧ 1997 by Academ ic Press