towards insight into properties and stabilities of complexes of ozone with co2, cs2 and sco species
TRANSCRIPT
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ORIGINAL RESEARCH
Towards insight into properties and stabilities of complexesof ozone with CO2, CS2 and SCO species
Abdolvahab Seif • Moein Goodarzi
Received: 3 September 2013 / Accepted: 19 October 2013
� Springer Science+Business Media New York 2013
Abstract The MP2 method in combination with the aug-
cc-pVXZ (X = D and T) basis set has been carried out to
examine the complexes between O3 and isostructure spe-
cies of CO2, CS2 and SCO. Two, two and four minima
have been located on the potential energy surfaces of O3–
CO2, O3–CS2 and O3–SCO complexes, respectively. The
results reveal that the stabilization of complexes should be
in the order O3–CS2 [ O3–SCO [ O3–CO2.
Keywords Ozone � Isostructure species �Atmospheric chemistry � MP2
Introduction
By now, the study of noncovalently bonded interactions is
one of the hottest subjects in material world, and has been
studied in numerous pamphlets of such systems [1, 2]. The
complexes formed through these interactions are very
important in many areas, such as atmospheric chemistry
and biochemical procedure.
Ozone (O3) is one of the most interesting species
in the atmosphere. It is incontrovertible that the exis-
tence of O3 in the atmosphere is important for life on
the Earth. Because, it absorbs solar radiation with a
wavelength which influences on our health. In the
troposphere, O3 is a harmful pollutant that causes dam-
age to glaze and respiratory tissues in animals and tis-
sues in plants. It can also act as a chemical oxidant by
adding oxygen atoms to other compounds. The largest
concentration of O3 is attained at approximately
4 9 1012 molecules/cm3 [3–5]. Because of its short-lived
nature, tropospheric O3 does not have strong global
effects, but has very strong radiative forcing effects on
regional scales. In fact, there are regions of the world
where tropospheric O3 has a radiative forcing up to
150 % of carbon dioxide [6].
Atmospheric sulphur chemistry plays an important role
in the Earth’s atmosphere [7, 8]. It is well accepted that
carbon disulphide (CS2) and carbonyl sulphide (SCO) are
two of the major pollutants in the atmosphere [9, 10].
The CS2 molecule gets out during volcanic eruptions
[11]. Swamps are also one of the major sources of this
molecule. The pollutants, which are derived from carbon
disulphide by photolysis, are great threats to human health
and global environment. Its atmospheric quality is greatly
affected by atmospheric particles, on which a lot of het-
erogeneous interactions occur.
The SCO molecule is the most abundant sulphur com-
pound naturally present in the atmosphere. It is emitted
from oceans, volcanoes and deep sea vents. The long
atmospheric lifetime of SCO makes it the major source of
stratospheric sulphate, though sulphur from volcanic
activity can be significant too [12]. As such, it is a sub-
stantial compound in the global sulphur cycle.
In the present work, we report for the first time
detailed examination of the stability and properties of
complexes including O3 molecule with one of CO2, CS2
and SCO molecules. This computational study can
provide valuable information in the atmospheric
chemistry.
A. Seif (&)
Department of Chemistry, Faculty of Science, University of
Kurdistan, Sanandaj, Iran
e-mail: [email protected]
M. Goodarzi
Department of Chemistry, Institute for Advanced Studies in
Basic Sciences (IASBS), Zanjan, Iran
123
Struct Chem
DOI 10.1007/s11224-013-0365-3
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Computational method
All calculations have been performed with the GAUSSIAN
03 quantum chemical package [13] using MP2/aug-cc-
pVXZ (X = D and T) level [14] along to the frozen core
approximation. Harmonic vibrational frequency calcula-
tions have been performed at the MP2/aug-cc-pVDZ
computational level to confirm the existence of all com-
plexes as local minima (with the number of imaginary
frequencies NIMAG = 0) and to provide the evaluation of
the zero–point energies (ZPEs).
Despite the complicated nature of O3 upon a multicon-
figuration scheme [15], many reports have focused on the
simple single-configuration types of calculations. In this
regard we can see that MP2, as one of the acceptable
computational levels, has attracted attention to investigate
of O3 complexes [16, 17].
In all complexes, the reported energies correspond to
that corrected from the inherent basis set superposition
error (BSSE) using the full counterpoise method [18].
The molecular electrostatic potential (MEP) on the
electron density isosurface of 0.001 a.u. has been
obtained and depicted using the WFA program [19]. The
atoms in molecules (AIM) methodology [20] have been
used with the AIM2000 [21] programs to analyse the
electron density calculated at the MP2/aug-cc-pVDZ
computational level. The natural bond orbital (NBO)
technique was performed to count the value of charge
transfer occurring at atomic charges using the NBO-3
program [22–24].
Results and discussion
The stabilization energies of the complexes in the
present work were calculated as the difference between
the energy of the complex and the sum of the ener-
gies of the isolated monomers in their minimum
configuration.
To determine the structural complexes, the different
orientations of CO2, CS2 and SCO species to O3 molecule
have been chosen. The b, c and d nomenclatures stand for
complexes of O3–CO2, O3–CS2 and O3–SCO, respec-
tively. Notice that the numbering that has been used in
nomenclature conform to the ordering of binding energy
(corrected with BSSE) at the MP2/aug-cc-pVTZ//MP2/
aug-cc-pVDZ level. In the present work, our results have
been accommodated within three sections. The first on
monomers and its characterizations have been discussed.
The second on the analyses of the dimers clustering and at
last the evaluation of the AIM and NBO analyses are
discussed.
Monomers
The O3 molecule has C2V symmetry, whereas other iso-
structure species are belonging to the more symmetrical
groups, CO2 and CS2 molecules have D?h symmetry and
SCO one has C?v symmetry.
The electronic feature of the monomers, which is of the
topmost interest in the study of non-covalent interactions,
is the MEP on the 0.001 a.u. electron density isosurface.
The 0.001 a.u. isosurface has been famed, since it has been
shown to resemble the experimental van der Waals surface
[25]. To identify basic and acidic sites for possible inter-
molecular interactions, the MEP is very useful implement.
To understanding of a more detailed of the electrostatic
characterization, it is worth to mention the presence of four
minima in the MEP of the O3 molecule, each twin of them
for lateral oxygen atoms. Figure 1 shows that O3 molecule
has two major regions on its electrostatic profile. Blue
colour indicates the high density of the presence of elec-
trons, whereas red refers to deficiency of the presence of
electrons. This approach mainly exists for other studied
monomers, CO2, CS2 and SCO. Minima for each of CO2
and CS2 (D?h) species and also for SCO (C?v) are shown
in Fig. 1. According to electrostatic potential profiles of
monomers along interaction, it is worth to underscore three
of the following points:
(a) According to the electrostatic potential profile of O3,
it seems that the surrounding of central oxygen atom
is mainly positive.
(b) Comparing profiles of CO2 and CS2 monomers reveal
that the substitution of both O-atoms in CO2 mono-
mer by S-atoms causes diminishing of deficiency
upon central atom and towards it to lateral atoms.
This treatment can be attributed to the decreasing of
electronegativity of S-atoms. Thus, the S-atoms of
CS2 are more positive than the O-atoms of CO2.
(c) The profile of SCO monomer shows that the head of
O-atom is much more negative than that of S-atom.
Heterodimers
O3–CO2 complexes
Figure 2 shows that association of CO2 monomer leads to
two minima, b1 and b2. b1 complex is formed when just
one of O-atoms of CO2 molecule attacks to both terminal O
atoms of O3. The distances of O���O interaction are 2.973
and 2.966 A at the MP2/aug-cc-pVDZ level. Table 1
shows that the binding energy of b1 complex (after BSSE
correction) is 8.32 kJ/mol at the MP2/aug-cc-pVTZ//MP2/
aug-cc-pVDZ level.
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b2 complex was found on the PES of O3–CO2 system.
This complex is formed through a linkage between terminal
O-atom of O3 and C-atom of CO2 (O���C interaction) with
bond length of 2.951 A at the MP2/aug-cc-pVDZ level. The
binding energy of this complex (corrected with BSSE) is
5.22 kJ/mol at the MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ
level.
These results show that b1 complex is 3.10 kJ/mol more
stable than b2 one. Note that our results are calculated at
the room situation. Hence, differences of temperature and
pressure, particularly in the atmosphere, may influence this
result.
O3–CS2 complexes
Similar to prior system, two minima, c1 and c2, were
located on the PES of O3–CS2 system as shown in Fig. 2.
c1 is the most stable complexes among all obtained com-
plexes for O3–CO2, O3–CS2 and O3–SCO systems. c1 is
12.04 kJ/mol more stable than initial reactants of O3 and CS2
Fig. 1 Molecular electrostatic
potential on the 0.001 a.u.
electron density isosurface of
monomers a O3, b CO2, c CS2
and d SCO
Table 1 Stabilization energies (kJ/mol) of O3–CO2, O3–CS2 and O3–SCO systems at the MP2 level
Complexes MP2/aug-cc-pVDZ MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ
EI EI ? BSSE EI ? BSSE ? ZPE EI EI ? BSSE
b1 -11.88 [-9.58] -6.87, 42 % [-3.26,65 %] -0.42 -10.84 -8.32
b2 -7.83 -4.40 1.19 -6.84 -5.22
c1 -14.78 [-16.91] -8.83, 40 % [-1.54, 90 %] -4.42 -15.23 -12.04
c2 -14.23 -8.88 -4.25 -14.55 -11.64
d1 -12.53 [-12.11] -7.59, 39 % [-1.79, 85 %] -2.08 -12.60 -10.03
d2 -12.70 -7.45 -1.94 -12.57 -9.81
d3 -8.06 -4.55 -0.10 -7.44 -5.68
d4 -7.74 -4.36 0.11 -7.17 -5.46
The values of in square brackets are at the MP2/6-311??G(d,p) level [23]. The BSSE contributions to the raw interaction energy are in
percentage form
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at the MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ level. In c1
complex, all three O-atoms of O3 present in intermolecular
interactions. Two of them have been emanated from the
connection of terminal oxygen atoms of O3 monomer with one
of S-atoms of CS2 monomer, with interaction distance of
3.256 A. The third interaction, with bond length of 3.061 A is
formed through the linkage of central O-atom of O3 to C-atom
of CS2 monomer. Note that interaction of central O-atom of O3
with C-atom of CS2 monomer appeals only in the c1 complex.
C2 is the second stable complexes among all obtained
complexes for O3–CO2, O3–CS2 and O3–SCO systems
which is formed through two interactions, O���S (3.113 A)
and O���C (2.968 A). The binding energy of this complex,
approaching to c1 complex, is 11.64 kJ/mol (corrected
with BSSE) at the MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ
level.
O3–SCO complexes
The latest system, considered in this work, has four minima
as shown in Fig. 1.
d1 complex is the most stable complex in the O3–SCO
system. In this complex, both terminal O-atoms of O3
molecule approach SCO molecule to form two interactions
of O���S (3.173 A) and O���C (2.916 A). As shown in
Table 1, the binding energy d1 complex is 10.03 kJ/mol at
the MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ level (cor-
rected with BSSE).
The second most stable complexes in the O3–SCO
system are d2 including two similar interactions of O���Cwith bond length 3.045 A at the MP2/aug-cc-pVDZ level.
The third and fourth minima located on the PES of this
system are d3 and d4, respectively. Although these two
Fig. 2 The representation of molecular graph of the minima obtained at the MP2/aug-cc-pVDZ level, b O3–CO2, c O3–CS2 and d O3–SCO
systems. The red and yellow dots represent the position of the bond and ring critical points, respectively
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complexes are very similar to each other, they have been
differed on the orientation of oxygen and sulphur atoms of
SCO towards the O3 monomer. It is mentionable that both
of them include one O���C interaction, in which O���Cinteraction of d3 complex is only 0.008 A shorter than that
of d4 complex. The computation of binding energies for
them shows that they should be 5.68 and 5.46 kJ/mol at the
MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ level, respectively.
The d3 and d4 complexes are the most unstable complexes
in the O3–SCO system.
Note that Venayagamoorthy and Ford [26] have recently
done molecular orbital studies of the vibrational spectra on
the complexes between O3 and each of CO2, CS2 and SCO
monomers at the MP2/6-311??G(d,p) level. They have
only reported the most stable complex for each of O3–CO2,
O3–CS2 and O3–SCO systems which are b1, c1 and d1,
respectively. As shown in Table 1, the reported binding
energy by Venayagamoorthy and Ford for b1, c1 and d1
complexes (at the MP2/6-311??G(d,p) level) are in good
agreement with those of the present work (without BSSE)
at the MP2/aug-cc-pVDZ level. While, comparison of the
corrected binding energy with BSSE shows that energy
values at the MP2/aug-cc-pVDZ level (in the present work)
are very different from those of MP2/6-311??G(d,p) level
(by Venayagamoorthy and Ford [26]). The values of BSSE
in both the present and the previous works are gathered in
Table 1.
It should be noted that the binding energies with the
Dunning basis sets are considerably larger than those of the
earlier work using a fairly large pople- type basis set.
As result, the binding energy of all complexes obtained
in the O3–CO2, O3–CS2 and O3–SCO systems can organize
in the order c1 [ c2 [ d1 [ d2 [ b1 [ d3 [ d4 [ b2.
This means that the most stable complexes belong to O3–
CS2 system. Therefore, this system plays more prodigious
role, from the atmospheric point of view.
AIM and NBO
Because of the presence of intermolecular interaction, it is
important to know the nature of interaction meticulously.
Thus, the usage of the Badar’s theory within AIM analysis
can be beneficial to analyse of interactions, especially weak
interactions. According to this theory, which is capable of
the topological analysis of the electron density, those points
of space where the gradient is hollow are characterized.
Three main kinds of these hollowed gradients, the so-called
critical points, are bond critical points, BCP (3, -1), ring
critical points, RCP (3, ?1) and cage critical points, CCP
(3, ?3). Note that the number (3) and sign (-1, ?1 and
?3) of the eigenvalues of these critical points have been
calculated after the solution of Hessian matrixes. The most
interested critical point, BCP, is located along a maximum
electron density trajectory that connects two atoms, known
as bond path.
These BCPs present electron density values between
0.0073 and 0.0103 a.u. and Laplacians between 0.0265 and
0.0356 a.u. as shown in Table 2. In Fig. 2, the corre-
sponding critical points and bond path of the three systems
are portrayed showing a diversity of complex graph forms.
The GC/VC ratio, being GC and VC the kinetic and potential
energy density at BCP, respectively, has been used as a
measure of the covalency in non-covalent interactions.
Values greater than 1 generally indicates a non-covalent
interaction without covalent character, while ratios smaller
than 1 are stating of the covalent nature of the interaction
[27]. The values of this quantity are around 1.2 that indi-
cates non-covalent nature of the interactions.
The small electron density, positive values of r2q and
-GC/VC \ 1 indicate that all intermolecular interactions
are weak interactions of non-covalent without any covalent
characters.
The electron density for each dataset shows a good
correlations between interatomic distance of the atoms
involved and qBCP (a.u.) and r2qBCP (a.u.). However,
previous reports have shown that this correlation should be
exponential (Fig. 3) [28, 29]. Thus, as the intermolecular
distance of the interacting atoms decreases, the values of
qBCP and r2qBCP increases.
The charge transfer values upon the formation of the
complexes are listed in Table 3. It is interest that the
maximum value of this quantity among all complexes is
belonging to the most stable complexes, c1 (0.009). Also,
O3 molecule has the role of an acceptor in O3–CS2, O3–
SCO systems, while it is a donor in O3–CO2 systems. The
Table 2 Interatomic distances (A) and bond critical point data (a.u.)
calculated at the MP2/aug-cc-pVDZ level
Complexes Interaction Interaction
distance
q r2q -G/V
b1 O���O 2.973 0.0087 0.0351 1.1616
O���O 2.966 0.0088 0.0356 1.1605
b2 O���C 2.951 0.0088 0.0324 1.2495
c1 O���S 3.256 0.0079 0.0265 1.1383
O���C 3.061 0.0074 0.0300 1.2037
O���S 3.256 0.0079 0.0265 1.1381
c2 O���C 2.968 0.0092 0.0317 1.1792
O���S 3.113 0.0103 0.0323 1.1113
d1 O���S 3.173 0.0094 0.0294 1.1112
O���C 2.916 0.0093 0.0332 1.2019
d2 O���C 3.045 0.0081 0.0291 1.2024
O���C 3.045 0.0081 0.0291 1.2023
d3 O���C 3.071 0.0074 0.0292 1.2474
d4 O���C 3.079 0.0073 0.0295 1.2438
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values of dipole momentum of complexes were listed in the
latest column of this table. These values are in range of
0.550–1.365 D. It should be noted that the minimum value
of dipole momentum among all systems is belong to the
most stable complexes c1 (0.550 D).
Conclusions
Ab initio calculations have been performed at the MP2/
aug-cc-pVDZ and MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ
levels to analyse the complexes at the O3–CO2, O3–CS2
and O3–SCO systems. The results can be summed as
follows:
(a) Our calculations reveal that the stability of three
systems can be organized in the order O3–CS2 [ O3–
SCO [ O3–CO2. The stability energies are in range
5.22–12.04 kJ/mol at the MP2/aug-cc-pVTZ//MP2/
aug-cc-pVDZ level.
(b) All possible interactions (regarding AIM analysis)
among atoms of monomers have been found in the
present work. Note that interaction of central O-atom
of O3 with C-atom of CS2 monomer appeals only in
the c1 complex.
(c) Based on AIM analysis, the small electron density,
positive values of r2qBCP and -GC/VC [ 1 indicates
that all intermolecular interactions in O3–CO2, O3–
CS2 and O3–SCO systems are weak interactions of
non-covalent with no covalent characters.
(d) The maximum value of charge transfer and the
minimum value of dipole momentum obtained are
belonging to the most stable complexes among three
systems.
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