2794
J. Phys. Chem. A 2010, 114, 2794–2798
First High Resolution Spectroscopic Studies and Ab Initio Calculations of Ethanetellurol
Roman A. Motiyenko,*,† Laurent Margulès,† Manuel Goubet,† Harald Møllendal,‡
Alexey Konovalov,‡ and Jean-Claude Guillemin§,|
Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523, UniVersité de Lille 1,
F-59655 VilleneuVe d’Ascq, France, Centre for Theoretical and Computational Chemistry (CTCC), Department
of Chemistry, UniVersity of Oslo, P.O. Box 1033 Blindern, NO-0315 Oslo, Norway, École Nationale Supérieure
de Chimie de Rennes, CNRS, UMR 6226, AVenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7,
France, and UniVersité européenne de Bretagne, Rennes, France
ReceiVed: December 22, 2009; ReVised Manuscript ReceiVed: January 19, 2010
The millimeter-wave rotational spectrum of ethanetellurol has been recorded and assigned for the first time.
The spectroscopic study has been complemented by high level ab initio calculations. Geometries, total electronic
energies, and harmonic vibrational frequencies have been determined at the MP2 level. A small-core relativistic
pseudopotential basis set (cc-pVTZ-PP) was employed to describe the tellurium atom. Two stable conformers,
synclinal and antiperiplanar, have been identified. Both theory and experiment have shown the synclinal
form to be more stable by 2 kJ/mol. The doublet structure observed in the rotational spectrum of synclinal
conformer is attributed to tunneling motion of tellurol functional group. The energy difference between 0+
and 0- substates split by tunneling has been determined from the observed spectra.
Introduction
Few studies of the physical properties of tellurols have been
reported in the past, presumably because conventional synthetic
approaches were not always efficient.1 Their kinetic instability,
toxicity, and repulsive smells are additional reasons for the
sparse literature on these compounds. However, an effective
synthetic procedure of tellurols, namely the reduction of
ditellurides by tributyltin hydride (Bu3SnH), was reported
recently.1 The use of diphenylditelluride as a catalyst in this
reaction later proved to be beneficial.2,3
This new and effective synthesis of tellurols has made it
possible to investigate the physical properties of this littleinvestigated class of compounds.2,3 The gas-phase acidities of
several tellurols, including that of the title compound, ethanetellurol (CH3CH2TeH), were the themes of one of these
investigations,2 which also included a quantum chemical study
of such properties. In another recent study,3 photoelectron
spectroscopy augmented by quantum chemical calculations were
performed for several tellurols. In the present work, these
investigations are extended to include the first study of the
rotational spectrum of a tellurol, namely ethanetellurol, assisted
by quantum chemical calculations.
Ethanetellurol belongs to a class of compounds with the
general formula CH3CH2XH, where X is a main-group 16
element (X ) O, S, Se, and Te). The rotational spectra of the
other members of this group were reported as CH3CH2OH from
the 1960s to very recently,4,5 CH3CH2SH6-11 in the 1960s and
1970s, and CH3CH2SeH the early 1980s.12,13
Two rotameric forms, where the C-C-X-H is antiperiplanar
(ap; obsolete, trans), or synclinal (sc; obsolete, gauche), may
exist for these compounds. This rotational isomerism is il* To whom correspondence should be addressed. Telephone: +33-320434943. Fax: +33-3-20337020. E-mail: motienko@phlam.univ-lille1.fr.
†
Université de Lille 1.
‡
University of Oslo.
§
ENSCR.
|
Université européenne de Bretagne.
Figure 1. The calculated structure of the sc (a) and ap (b) conformers
of ethanetellurol.
lustrated in Figure 1 in the case of the title compound, where
the two forms are abbreviated ap and sc, respectively. Precise
experimental values for the energy difference between the
antiperiplanar and synclinal forms are now known for
10.1021/jp912082b  2010 American Chemical Society
Published on Web 02/05/2010
Rotational Spectrum of Ethanetellurol
CH3CH2OH, where the antiperiplanar form is 0.5 kJ/mol more
stable than the synclinal form,5 whereas the opposite conformational preference is found for the sulfur and selenium
analogues. The synclinal rotamers are more stable than the
antiperiplanar conformers in the cases of CH3CH2SH11 and
CH3CH2SeH13 by 1.70(18) kJ/mol and 0.79 kJ/mol, respectively.
A successful investigation of a delicate conformational
equilibrium such as the one presented by ethanetellurol requires
experimental methods possessing high resolution. Rotational
spectroscopy meets this requirement because of its superior
accuracy and resolution, making this method especially well
suited for conformational studies of gaseous species. The
spectroscopic work has been augmented by high-level quantum
chemical calculations, which were conducted with the purpose
of obtaining information for use in assigning the rotational
spectrum and investigating properties of the potential energy
hypersurface. To our knowledge, there is no published investigation of the potential energy surface of ethanetellurol. Its gas
phase acidity has been previously studied, together with other
sulfur, selenium, and tellurium containing compounds, using a
G2(ECP) approach.2 Although the accuracy of this level of
theory is certainly good enough to account for the thermochemical properties, calculations have been here performed at
a higher level of theory, using larger basis sets and a smallcore relativistic pseudopotential. Indeed, more accurate values
of the spectroscopic parameters are needed to help in interpreting
the rotational spectra.
Experimental Methods
Caution. Ethanetellurol is malodorous and potentially toxic.
All reactions and handling should be carried out in a wellventilated hood.
Synthesis. The synthesis of this compound, which has already
been reported,1 is repeated in the Supporting Information for
the convenience of the reader.
Stark Spectroscopy Experiment. The spectrum of ethanetellurol was studied in the 21.8-79 GHz frequency interval by
Stark-modulation spectroscopy using the microwave spectrometer of the University of Oslo. Details of the construction and
operation of this device have been given elsewhere.14,15 The
spectrometer has a resolution of about 0.5 MHz and measures
the frequency of isolated transitions with an estimated accuracy
of about 0.1 MHz. The experiments were performed at a
pressure of roughly 10 Pa with the cell cooled to about -30 °C
by dry ice.
The spectrum observed under these conditions was of
intermediate to low intensity and quite dense. It is assumed that
the spectral weakness was caused at least in part by the presence
of considerable amounts of impurities. The high Ka aR-type
transitions of this prolate rotor (κ ∼ -0.99) were first recorded
and seen to be the strongest absorptions of the spectrum. The
intensities of these peaks were checked from time to time and
were found to diminish slowly with time, presumably because
of reactions taking place in the cell. The cell therefore had to
be filled with fresh sample every two hours.
Conventional Absorption Spectroscopy Experiment. Initial
experiments with the microwave spectrum of ethanetellurol have
been carried out using the spectrometer in Lille. The rotational
spectrum has been recorded in the frequency range 75-300
GHz. The accuracy of the frequency measurement for an isolated
line is estimated to be better than 0.03 MHz. The spectrometer
is built according to typical scheme, [source of radiation]-[absorption cell]-[detector]. As a source of radiation, we use two-step
frequency multiplication system, based on Agilent E8752D
J. Phys. Chem. A, Vol. 114, No. 8, 2010 2795
synthesizer (12.5-17 GHz) whose frequency is multiplied by
6 and amplified in the frequency range 75-110 GHz (Spacek
Laboratories Inc. active sextupler) at the first stage and
additionally multiplied by 2, 3, or 5 (Virginia Diodes Inc.
multipliers) at the second. The emitted microwave signal passes
through the absorption cell and is detected by an InSb liquid
He-cooled bolometer. A 1.2 m Pyrex glass tube with Teflon
windows is used as an absorption cell. During the experiments
the cell was kept at room temperature. Therefore, to minimize
the observation of spectra of decomposition products, the sample
of ethanetellurol was continuously injected via a side opening
at one end of the cell and pumped out via another side opening
at the other end. The sample was evaporated at -70 to -80
°C. This temperature was found to be optimal to provide enough
vapor pressure in the cell (about 1 Pa) and at the same time to
avoid fast decomposition of the sample. The spectra recorded
under these conditions seemed to contain no significant impurities, since all the strongest features observed were assigned to
ethanetellurol.
Computational Methods
All the calculations of this study were performed using the
Gaussian03 software package.16 The geometries were fully
optimized and the frequencies were calculated at the MP2 level.
All electrons were included in the correlation calculation
(MP2(full)). In the case of heavy atoms like tellurium, inner
core electrons are very close to the nucleus, so that their velocity
is close to the speed of light. Therefore, relativistic effects are
taken into account. For this reason, the small-core relativistic
pseudopotential basis set (cc-pVTZ-PP) was employed to
describe the tellurium atom.17 Consequently, the cc-pCVTZ basis
set with extra core/valence functions was used for the carbon
atoms.18,19 The standard correlation-consistent polarized triple
valence basis set (cc-pVTZ) of Dunning and co-workers18,19 was
employed to describe the electrons of the hydrogen atoms. Basis
sets were obtained from the EMSL basis set library.20,21 The
combination of MP2 level of theory with correlation-consistent
polarized triple valence basis sets type was chosen because it
is well-known to offer the best compromise between calculation
time and accuracy for analogous molecules.22,23 Finally, the
transition states existing between the stable conformations were
characterized using the QST2 procedure, as implemented in the
Gaussian03 software package.
Geometry optimizations led to two stable conformations
denoted hereafter ap (a planar skeleton with a C-C-Te-H
dihedral angle of 180°) and sc (with a C-C-Te-H dihedral
angle of 63° from syn). The stable conformers are displayed in
figure 1 and geometrical parameters are given in Table S1 in
the Supporting Information. Calculations with other starting
point geometries have been performed, for example, for the syn
geometry. In each case, geometry optimizations converged to
one of the two aforementioned conformations, showing that
these are the only stable forms of ethanetellurol. The transition
states along the tellurol internal rotation coordinate (C-Te bond
torsion) have also been characterized. Two saddle points,
exhibiting only one imaginary frequency, have been found, one
with a syn conformation (C-C-Te-H dihedral angle of 0°,
denoted hereafter syn-TS) and another one with an anticlinal
conformation (C-C-Te-H dihedral angle of 128°, denoted
hereafter ac-TS). It is worth noting that the sc and ac-TS forms
have two equivalent conformations with opposite sign of the
C-C-Te-H dihedral angle. In addition, the barrier to internal
rotation of the methyl group (C-C bond torsion) have been
examined for the sc conformer (denoted hereafter rot-TS). The
2796
J. Phys. Chem. A, Vol. 114, No. 8, 2010
TABLE 1: Relative Energies with Respect to the sc
Conformer ∆Esca
a
conformation
∆Esc/kJ.mol-1
sc
ap
syn-TS
ac-TS
rot-TS
0.00
2.01 (2.18)
4.49 (5.23)
4.46 (4.70)
14.98 (15.43)
The ZPE corrected energies are reported in parentheses.
relative energies of each calculated conformation with respect
to the sc conformer are listed in Table 1. For all forms, the
total electronic energy has been ZPE corrected with subtraction
of the frequency, in the stable conformers, corresponding to
the imaginary one in the TS (i.e., the C-Te torsional mode).
Calculated harmonic frequencies for the sc and ap conformers
are listed in Table S2 in the Supporting Information.
These results warrant comments. First, two stable conformers,
ap and sc were expected because the torsion angles associated
with the C-Te bond put the groups attached to these two
adjacent atoms in a staggered conformation. Moreover, it agrees
very well with analogous molecules containing atoms of the
sixteenth column (ethanol, ethanethiol, and ethaneselenol).
Second, in the present case, the sc conformer is calculated to
be more stable than the ap by about 2 kJ/mol. This is also similar
to the results for the analogous thiol and selenol. For ethanol,
the ap and sc conformers have about the same energy, with a
slight preference for ap (about 0.5 kJ/mol).5 For ethanethiol, sc
is unambiguously the most stable rotamer from considerations
of relaxation processes in a supersonic expansion.24 A previous
study yielded an energy of sc of approximately 1.7 kJ/mol below
the energy of ap.11 For ethaneselenol, sc is estimated to be more
stable than ap by about 1 kJ/mol from semiempirical calculations.13 Finally, the exploration of the potential energy surface
agrees with the results from the analogous molecules as well.
For ethanol, ac-TS and syn-TS were found to lie about 4.7 and
5 kJ/mol, respectively, above the stable conformations.5 For
ethanethiol, ac-TS and syn-TS were found to lie about 6 and
6.5 kJ/mol, respectively, above the sc conformer.11 For ethaneselenol, ac-TS and syn-TS were found to lie about 5.2 and 5.8
kJ/mol, respectively, above the energy of sc.13 In each case,
the syn-TS is at a higher energy than the energy of ac-TS, so
that the most favorable way of interconversion from sc to ap is
to pass by the ac-TS. One should note that all the energy values
for ethanol, ethanethiol, and ethaneselenol were obtained
semiempirically, while the results on ethanetellurol obtained in
this study come only from ab initio calculations. Therefore, the
comparative analysis presented above should be considered with
caution.
Assignment and Analysis of the Spectra
The results of ab initio calculations facilitated significantly
the assignment of the rotational spectrum of ethanetellurol. On
the basis of the calculated dipole moment components (µa )
1.48 D, µb) 0.3 D for sc and µa ) 1.43 D, µb ) 0.6 D for ap
conformation) one could expect to observe a strong µa spectrum.
Indeed, the first spectra recorded using the Lille spectrometer
in the frequency range 150-170 GHz revealed the presence of
a series of strong aR0,1 bands. For this type of bands, the
separation between their origins is approximately equal to the
sum of the rotational constants, ∆ν ) B + C.25 The experimental
value of ∆ν was found to be ∼5.7 GHz and close to theoretical
values of 5.69 GHz for sc- and 5.85 GHz for ap-ethanetellurol.
Motiyenko et al.
We have also found that each band consisted of at least three
subbands. The position of subbands and the distribution of their
relative intensities corresponded well to isotopic shifts (lighter
species spectrum is shifted to higher frequencies) and isotopic
abundances of the tellurium atom (130Te, 34%; 128Te, 30%; and
126
Te, 18%). Finally, the high resolution analysis has shown
that each line in the band has a doublet structure, indicating
the presence of internal rotation in the molecule. The separation
between doublet components varies from 0.7 to 1.5 MHz
depending on frequency range. We have analyzed two possible
origins of internal rotation. First CH3 functional group torsion
has been excluded from consideration since the calculated value
of the torsional barrier (15 kJ/mol) is too high to provide large
splittings. For example, for a similar molecule such as ethyl
cyanide, the barrier height is estimated to be 12.9 kJ/mol and
no torsional splittings have been observed in millimeter-wave
spectra.26,27 Second, we have found that the separation between
the components of a doublet depends on the J quantum number,
and does not depend on the position within a band, that is, the
Ka quantum number. According to the theoretical estimations,
such splittings can be caused by Te-H functional group
tunneling motion. Therefore, the observed rotational transitions
having doublet structure were assigned to synclinal conformation
of ethanetellurol which has double minima potential and a barrier
to Te-H tunneling of medium height (about 5 kJ/mol). This
value is comparable with corresponding values of barrier height
to S-H (6 kJ/mol) and Se-H (5 kJ/mol) tunneling of ethanethiol
and ethaneselenol. For both of these molecules, the tunneling
splittings have been observed in the spectra of sc conformation.
The initial assignment of the antiperiplanar conformation on
the basis of millimeter-wave measurements in Lille was quite
problematic due to the high density of the spectra and presumably low intensity of rotational lines. Therefore, we turned to
less crowded lower frequency spectra recorded using the
spectrometer in Oslo. The differences of the rotational constants
between ap and sc obtained in the quantum chemical calculations
were added to the experimental rotational constants of sc and
used to predict the aR-spectrum of ap. The spectrum of the most
abundant isotopologue (130Te) of ap was found in this manner
close to its prediction. The 128Te and 126Te isotopologue spectra
were then readily assigned. The pseudoinertial defect Ic - Ia Ib ) -6.47 × 10-20 u m2 is taken as an additional evidence
that ap had indeed been assigned, because this value is typical
for a compound having a symmetry plane and two pairs of sp3hybridized out-of-plane hydrogen atoms. The corresponding
values for the antiperiplanar forms of the other CH3CH2XH
compounds are -6.405(2) × 10-20 u m2 for CH3CH3OH,28
-6.389(2) × 10-20 u m2 for CH3CH332SH,9 and -6.424(3) ×
10-20 u m2 for CH3CH380SeH.11 The following analysis has also
lead to the assignment of ap conformation of ethanetellurol in
the spectra recorded in Lille.
Analysis of sc Conformation. Because of the effect of
tunneling through the barrier to tellurol internal rotation, the
ground state of sc-ethanetellurol is split into symmetric and
antisymmetric 0+ and 0- substates. In the internal axis system
the ab plane is formed by three heavy atoms C-C-Te, and
for sc conformation the C-C-Te-H dihedral angle is about
63° from syn. Taking this configuration into account one can
see that the tunneling motion does not change the sign of µa
and µb dipole moment components, or equivalently, that µa and
µb are even functions of TeH internal rotation angle. In order
that the transition dipole moment matrix element ⟨ψi|µx|ψj⟩(x
) a,b) to be nonvanishing, the wave functions ψi and ψj should
be of the same symmetry. Thus, for sc-ethanetellurol a- and
Rotational Spectrum of Ethanetellurol
J. Phys. Chem. A, Vol. 114, No. 8, 2010 2797
TABLE 2: Spectroscopic Constants for Various Isotopomers of sc Conformation of Ethanetellurol
130
A (MHz)
B (MHz)
C (MHz)
DJ (kHz)
DJK (kHz)
DK (kHz)
d1 (kHz)
d2 (kHz)
HJ (Hz)
HJK (Hz)
HKJ (Hz)
E*J (kHz)
E*2 (kHz)
E*JJ (Hz)
E*JK (Hz)
∆E (MHz)
Fbc (MHz)
N
σ (MHz)
σwb
a
Te
25605.359(73)
2865.67988(30)
2721.05960(30)
1.108067(58)
-9.02495(45)
[175.1]a
-0.109246(18)
-0.003192(13)
0.000406(10)
-0.007534(77)
-0.81180(95)
-6.736(38)
-5.259(24)
0.1615(93)
2.85(10)
656.59(14)
6.3757(27)
734
0.067
0.83
130
128
Te theory
25948.14
2891.240
2746.340
1.070
-10.31
175.1
-0.112
-0.00630
Te
25607.048(89)
2873.11816(35)
2727.77227(35)
1.113647(57)
-9.04527(46)
[175.1]a
-0.110129(21)
-0.003212(14)
0.000403(10)
-0.007499(82)
-0.8216(10)
-6.798(38)
-5.289(27)
0.1663(91)
3.00(11)
657.34(14)
6.4058(28)
752
0.057
0.86
126
Te
25608.577(71)
2880.78479(35)
2734.69051(35)
1.119542(55)
-9.06333(46)
[175.1]a
-0.111040(18)
-0.003271(13)
0.000423(10)
-0.007484(86)
-0.8223(10)
-6.867(35)
-5.339(24)
0.1621(88)
2.83(12)
656.90(21)
6.4408(35)
674
0.056
0.74
125
Te
25609.261(93)
2884.702134(42)
2738.223547(42)
1.122542(77)
-9.06981(78)
[175.1]a
-0.111512(21)
-0.003319(16)
0.000421(14)
-0.00664(19)
-0.8264(29)
-6.974(49)
-5.342(28)
0. 193(12)
3.00(23)
657.25(31)
6.4496(41)
433
0.026
0.83
124
Te
25610.353(83)
2888.693977(52)
2741.820195(52)
1.125723(82)
-9.0783(11)
[175.1]a
-0.111946(25)
-0.003270(16)
0.000438(14)
-0.00618(21)
-0.8266(41)
-6.799(58)
-5.402(30)
0.138(13)
2.47(29)
658.98(20)
6.4419(52)
375
0.029
0.73
Fixed to ab initio value. b Unitless rms deviation of the fit.
b-type type transitions can occur only within each substate
(selection rules: 0+ r 0+ and 0- r 0-). Because the µc dipole
moment component changes sign with tunneling, c-type transitions connect two substates (selection rules: 0+ r 0- and 0r 0+).
The Hamiltonian used for treating the tunneling substates was
set up by a combination of pure rotational and Coriolis coupling
terms: H ) HR + HC. The rotational term is defined in such a
way that it allows one to fit the rotational constants averaged
for 0+ and 0- substates.29 It is written as HR ) HS + H∆ where
HS represents the standard Watson’s S-reduction Hamiltonian30
in Ir representation and H∆ is a Hamiltonian of centrifugal
distortion corrections. In terms of rotational angular momentum
J and its components, Jz and J( ) Jx ( iJy, the term H∆ is
expressed as
2
2
2
2
4
H∆ ) E* + E*J
+ E*J
J
K z + E*(J
2 + + J-) + E*
JJJ +
E*JKJ2Jz2 + ... (1)
where E* is a half energy difference between 0+ and 0substates, - 2E* ) ∆E ) E(0+) - E(0-). Compared to a typical
approach when each substate is described by a separate rotational
Hamiltonian, the model chosen in the present study is proved
to provide fewer correlations between rotational constants, which
can be very important especially at the initial stage of an
assignment. In addition, a unique set of rotational constants
allows more straightforward comparison with corresponding ab
initio values. The Coriolis coupling term describing the interaction between tunneling substates is defined as
HC ) Fbc(JxJy + JyJx)
(2)
It should be noted that in eqs 1 and 2 the Ir representation (x )
b, y ) c, z ) a) is used.
The predictions and fits for the sc-ethanetellurol spectrum
have been undertaken using Pickett’s SPCAT/SPFIT programs.31
The rotational parameters obtained as the results of the fit for
all isotopologues studied are listed in the Table 2. The
frequencies of assigned rotational transitions are listed in Tables
S3-S7 of Supporting Information. Besides the most abundant
isotopic species of tellurium 130Te, 128Te, and 126Te, we have
observed the spectra of ethanetellurol containing less abundant
species like 125Te (7%) and 124Te (4.7%). In Table 2, we have
also listed the theoretical values of rotational and centrifugal
distortion constants calculated for CH3CH2130TeH species. In
comparison with experimental values one can see that the
rotational constants have been calculated with nearly 1% error
which is a good result for ab initio calculations. For the
centrifugal distortion constants, the agreement is less good, but
at least the order of magnitudes and signs agree for all of them.
Because of the lack of b- and c-type transitions, the DK
parameter could not be determined and it has been fixed in the
fit to its ab initio value. The value of the energy difference
between 0+ and 0- substates ∆E found as a global solution of
the tunneling problem is about 660 MHz (0.022 cm-1) and
seems to vary slightly with isotopic species.
Analysis of ap Conformation. The initial difficulties in the
assignment of the spectrum of the antiperiplanar conformation
of ethanetellurol were caused by relatively low intensities of
its lines. It was found that typically its lines are 2-2.5 times
less intense than those of sc. This is in agreement with
theoretical results predicting the sc conformation to be 2 kJ/
mol (160 cm-1) more stable than ap. As an illustration of the
observed relative intensities we provide a portion of spectra
(Figure 2) of unresolved a-type doublet 347-337 for both
conformations.
The observed microwave transitions of ap ethanetellurol were
fitted to the usual Watson S-reduction Hamiltonian in Ir
representation. However, we have found that this model has a
limitation in the case of ap conformation; it allows one to fit
within experimental accuracy only low Ka transitions up to Ka
) 4. In principle we can also fit higher Ka transitions by
including centrifugal distortion correction of higher orders, but
it leads then to severe convergence problems and unrealistic
values of the corresponding centrifugal distortion parameters.
The possible explanation of the observed perturbations comes
from consideration of the potential function which can no longer
be expanded in a fast convergent Taylor series. Theoretical
estimations provide the value of the barrier to Te-H internal
rotation for the ap conformation to be only 2.5 kJ/mol (200
2798
J. Phys. Chem. A, Vol. 114, No. 8, 2010
Motiyenko et al.
quantum chemical calculations, is now being applied to another
molecule containing a tellurium atom, vinyltellurol (H2Cd
CHTeH). Results of this study will be published shortly.
Acknowledgment. A.K. thanks The Research Council of
Norway for financial assistance through Contract 177540/V30.
J.-C.G. thanks the Centre National d’Etudes Spatiales (CNES)
for financial support. Jean Demaison is gratefully acknowledged
for helpful discussions on basis set choice.
Figure 2. An example of relative intensities distribution for 347-337
transition of ap and sc conformers of ethanetellurol.
TABLE 3: Spectroscopic Constants for Various Isotopomers
of ap Conformation of Ethanetellurol
130
A (MHz)
B (MHz)
C (MHz)
DJ (kHz)
DJK (kHz)
DK (kHz)
d1 (kHz)
d2 (kHz)
HJ (Hz)
N
σ (MHz)
σwb
a
Te
25051.85(18)
2973.3668(12)
2751.64087(82)
1.38393(16)
-11.73(12)
[169.4]a
-0.16489(24)
-0.00524(13)
38.6(57)
133
0.099
1.05
130
Te theory
25292.86
3011.15
2783.97
1.339
-14.40
169.4
-0.156
-0.00366
128
Te
25057.61(43)
2980.9628(17)
2758.18551(85)
1.39207(71)
-11.05(15)
[169.4]a
-0.16819(63)
-0.00550(42)
75.5(88)
85
0.091
0.85
126
Te
25060.98(24)
2988.7754(18)
2764.93365(90)
1.39749(27)
-11.36(20)
[169.4]a
-0.16886(36)
-0.00628(20)
68.(10)
103
0.084
0.98
Fixed to ab initio value. b Unitless rms deviation of the fit.
cm-1). A rigorous treatment of the rotational spectra of the ap
conformation requires the use of a more appropriate model
which takes into account the shape of potential function and is
beyond the scope of the present study. Therefore we present
here only the results obtained using the S-reduction. The
rotational parameters of ap-ethanetellurol obtained as the result
of least-squares fit are listed in the Table 3. The frequencies of
assigned rotational transitions are listed in Tables S8-S10 of
Supporting Information.
Conclusions
This paper presents the results of the studies of the ethanetellurol millimeter-wave rotational spectrum, which has been
recorded and assigned for the first time. The assignment was
supported by high level ab initio calculations taking into account
relativistic effects of the tellurium atom. In the present study, a
good agreement between the results of quantum chemical
calculations and experimental observations has been achieved.
As expected, two stable conformations (ap and sc) have been
identified in the spectra and the sc conformer is found to be the
most stable by 2 kJ/mol from theoretical consideration as well
as from experimental observations. Calculated and experimental
values of the rotational constants of sc and ap conformations
agree within 1% accuracy. For both rotamers, the rotational
spectra of the three most abundant isotopic species of the
tellurium atom have been studied. In addition, the more intense
spectrum of sc-ethanetellurol has allowed us to perform an
analysis of its two less abundant species, namely 125Te and 124Te.
The approach used in the present study, which is a combination
of high resolution millimeter-wave spectroscopy and high level
Supporting Information Available: Synthesis of ethanetellurol, calculated molecular structure and harmonic vibrational
frequencies, rotational line assignments, measured frequencies,
experimental uncertainties and deviations from the final fits for
studied isotopologues of sc and ap conformations of ethanetellurol. This material is available free of charge via the Internet
at http://pubs.acs.org.
References and Notes
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