1A06
UCCSD, UQCISD, and UMP2 studies on O2•••HF/FH van der Waals complexes: A
prospective on the structure, properties and topology
Pradeep R Varadwaja, Ian Loveb, Kentarou KawaguchiaaDepartment of Chemistry, Faculty of Sciences, Okayama University, Tsushima-Naka 3-1-1,Okayama-Ken, Okayama-shi, Japan 700 8530, b Department of Chemistry & Chemical
Technology, National University of Lesotho, Roma 180, Lesotho

Introduction
Molecular O2 (triplet spin state, X³Ȉ¯g) is aninteresting open shell system of atmosphericimportance. Thus, its interaction withmolecular HF (singlet spin state) should
presumably add insight for the understandingof weak interaction. The O2⋅⋅⋅HF complex has
been studied several times theoretically for its
electronic structure, properties and vibrational
characteristics using high level ab initio
techniques1,2 and eventually, identified andanalyzed experimentally using FTMW3 and IR
spectroscopic methods4,5. In all these studies,
attention has been given to the complexes ofO2⋅⋅⋅HF whilst there is almost no study oncomplexes formed between O2 and the F endof HF. In this work, we have investigated allthe possible types of complexes formed
between O2 and HF/FH. The equilibrium
structures,electronicandvibrational
properties, and topology of electron charge
density at bond critical points of the studied
systems are analyzed, compared, andpresented.
Results and Discussion
Figure 1 shows the UCCSD/Aug-CC-pVDZ
optimized configurations of the complexes ofO2⋅⋅⋅HF and O2⋅⋅⋅FH examined. Figures a andb are the two close global minima with bent
geometry, c (T-shape), d (linear), and e (quasilinear) are first order saddle point structures ofO2…HF whilst f (T-shape), g (linear), h(quasi-linear), i (bent) and j (bent) are allminima on the O2…FH hyper-surface. The
global minima a and b are found to be similar
to that reported previously at the UCCSD(T)/aug-cc-pVNZ (N = D, T)2 although aninconsistency has been found while comparing
with the T-shape complex of O2…HF, which
has been reported as a minimum. The saddle
point structures are confirmed by an analysisof the O2…HF/FH intermolecular bending
frequencies (O2…HF/HF bend, see Table 1).

Figure 1: UCCSD/aug-cc-pVDZ optimized
geometries of the complexes examined.
Some physical properties of the complexes aresummarized in Table 1. First of all, the intermolecular bond distances range from 2.220(O2..HF bent) to 3.202 Å(O2..FH T-shape)
which are less than or close to the sum of thevan der Waals radii of atoms involved in bond

critical points (see Figure 2) (electron density
at bcp: ~ 0.0097 au for a and b; ~0.0052 au for
T-shape, and ~0.0056 au for linear), positive
values of Laplacian of charge density (∇2ρ) atbcp (0.038 au for a and b, 0.021 au for Tshape; 0.024 au for linear), mutual penetration
for all, loss of charge on H (0.0034e for a andb; 0.0008e for T-shape; 0.0023e for linear),formation (H = 1.20 Å, O = 1.55 Å, and F =1.47 Å). The dipole moment enhancement(results from an inductive effect) is an
important measure of an interaction and isreflected upon complex formation. As shownin Table 1, there is no regular ordering among
the values of ∆µ (compared with ∆E) in the setof complexes examined, however, the mostComplex typeO2…HF bent (120)O2…HF bent (123)O2…HF T-shape
O2…HF linear
O2…HF quasi-linear
O2…FH Tshape
O2…FH linear
O2…FH quasi-linear
O2…FH bent (120)O2…FH bent (123)∆ r( ΗF)
0.00090.00110.00030.00030.0004-0.0003-0.0004-0.0005-0.0003-0.0003µ2.134
2.147
2.008
2.103
2.104
1.88
1.912
1.912
1.884
1.885

stable complex is accompanied by a largest
value of ∆µ.
Table 1: Physical parameters of O2…HF andO2…FH complexes obtained from theUCCSD/ aug -ccpVDZ level.
Figure 2: The ∇2ρ
contour map ofO2…HF(bent,∠OOH ≈ 120o)complex.
Furthermore, theH-bonded complexes were examined to bered-shifted (∆ν) with a concomitant elongationof the HF bond (∆r(HF)) whilst the complexes
with O2 weakly bonded to the F end of HF areblue-shifted with a concomitant HF bondcontraction. A red-shift of 15 cm-1 is predicted
for the HF stretch of O2…HF bent complex(∠OOH ≈ 120o), which is in agreement with ashift of 12.9 cm-1 observed experimentally4.
The UQCISD and UMP2 results are inconsistent with those obtained from theUCCSD level, and analyzed.
Analysis of the bonding features using thequantum theory of atoms in molecules(QTAIM) reveals that the existence of bond

∆µ
0.324
0.337
0.198
0.293
0.294
0.07
0.108
0.108
0.080
0.081

∆E-4.46-4.38-2.38-2.81-2.81-2.21-2.32
-2.25
-1.85
-1.84

O….H/F2.22012.22792.56032.37152.37293.20243.048
3.01373.12883.1264∆ν O2..FH/HF bend
-15
36.4
-23
38.7
-4.7-142.6
-3.7
-53
-3.3
-50
1.8
30.4
4
40.6
3.4
34.3
1.1
5.8
1.2
7.2

energetic destabilization of H atom, dipolarpolarization, and H atom volume decreased
for all the complexes satisfying the eightnecessary criterions of Popelier & Koch's
criteria for hydrogen bonds6. Thus asexpected, the bonding effect is greater for thea and b complexes compared to the othergeometries. It is also evident from thisanalysis that the O2⋅⋅⋅HF bent configuration(∠OOH ≈120/123o) satisfies the necessary andsufficient conditions of a hydrogen bondedinteraction whilst the O2⋅⋅⋅FH impropercomplexes are at the extreme end of weakinteractions.
References
1. A. M. Sapse, J. Chem. Phys. 78 (1983) 5733
2. W. M. Fawzy, J. Chem. Phys. 124 (2006)
164303. References therein
3. S. Wu, G. Sedo, E. M. Grumstrup, K. R.
Leopold, J. Chem. Phys. 127 (2007) 204315.
4. W. M. Fawzy, C. M. Lovejoy, D. M. Nesbitt,
J. T. Hougen, J. Chem. Phys. 117 (2002) 693,
References therein
5. R. D. Hunt, L. Andrews, J. Chem. Phys. 86(1987) 3781
6. U. Koch, P. L. A. Popelier, J. Phys. Chem.
99 (1995) 9747.