Experimental and theoretical characterization of H2OOO +

Article abstract of DOI:10.1021/ja037125z

This report presents the preparation and characterization of H₂OOO⁺, an important intermediate in water-oxygen chemistry. The H₂OOO⁺ cation was produced by co-deposition of H₂O/Ar with radio frequency discharged O₂/Ar at 4 K and was identified by four fundamental infrared absorptions. Quantum chemical calculations indicate a doublet ground state with a H₂O-O₂hemi-bonded C_s structure. Copyright

Full text of DOI:10.1021/ja037125z

Published on Web 08/30/2003
Experimental and Theoretical Characterization of H2OOO+
Mingfei Zhou,*,† Aihua Zeng,† Yun Wang,† Qingyu Kong,† Zhi-Xiang Wang,‡ and
Paul van Rague Schleyer‡
Shanghai Key Laboratory of Molecular Catalysts and InnoVatiVe Materials, Department of Chemistry &
Laser Chemistry Institute, Fudan UniVersity, Shanghai 200433, P.R. China, and Center for Computational Quantum
Chemistry, Computational Chemistry Annex, UniVersity of Georgia, Athens, Georgia 30602-2525
Received July 8, 2003; E-mail: mfzhou@fudan.edu.cn
Detailed knowledge concerning the interaction between water
and oxygen is of fundamental importance in biological, atmospheric,
and environmental sciences. For instance, photonucleation, an
important atmospheric phenomenon, was proposed to involve the
initial formation of a van der Waals complex, [H2O‚O2], followed
by its conversion into a charge-transfer complex, [H2O+O2-], upon
UV irradiation.1,2 Antibodies use H2O as an electron source in
biological systems. This facilitates the interaction of water with
singlet O2 to form H2O3, the first intermediate in a reaction cascade
which eventually gives H2O2.3,4 The [H2O‚O2]+ ion, existing in the
ionosphere, is assumed to be an important intermediate in the
formation of proton hydrates, H+(H2O)n,5-10 from O2+. The kinetics
and mechanism of photodissociation of the [H2O‚O2]+ cation have
been studied, and, without sophisticated characterization, the cation
was assumed to be an ion-molecule complex depicted as
O2+‚H2O.5-10 We now characterize the [H2OOO]+ cation spectro-
scopically as well as theoretically and show that a 3c-1e bond is
involved, instead of a simple ion-molecule complex.
Figure 1. IR spectra in the 3475-3320 cm-1 region from co-deposition
of H2O/Ar with discharged O2/Ar at 4 K. (a) 1.0% H2O/Ar and 1.5% O2/
Ar, deposited sample, (b) spectrum after irradiation at λ > 250 nm, (c)
1.0% H2O + 0.1% CCl4/Ar and 1.5% O2/Ar, deposited sample, and (d)
0.5% H216O + 0.5% H218O/Ar and 1.5% 18O2/Ar, deposited sample.
Table 1. Infrared Absorptions (in cm-1) Observed for Various
H2OOO+ Isotopomers in Solid Argon
The H2OOO+ cation was prepared by condensation of H2O/Ar
and O2/Ar via radio frequency discharge. Briefly, two separated
gas streams containing O2/Ar and H2O/Ar were co-deposited onto
a 4 K CsI window simultaneously. One of the gas streams was
subjected to discharge from a Tesla coil. The H2O/Ar (1:500 to
1:100) and O2/Ar (1:50 to 1:100) mixtures were prepared from
distilled water and high purity oxygen and argon. Infrared spectra
were recorded on a Bruker Equinox 55 spectrometer at 0.5 cm-1
resolution using a DTGS detector.
OH asy str.
OH sym. str.
O−O str.
H O−O str.
2 2
H2OOO+
3430.7
2555.5
3430.4
3416.2
2555.4
3383.8
3384.0
3341.7
2449.6
3341.0
3334.9
2449.0
2499.7
2499.7
731.0
606.3
726.8
724.2
598.7
D2OOO+
1601.1
1502.2
H2O18O18O+
H218OOO+
D2O18O18O+
HDOOO+
1511.4
1515.9
HDO18O18O+
Condensation of the H2O/Ar products at 4 K after discharge
resulted in OH (3547.9 cm-1),11 HOO (3412.1, 1388.3, and 1100.7
cm-1),12,13 H2O‚OH (3451.6 cm-1),14 and unidentified 767.8 cm-1
absorption splitting. The infrared absorptions with different isotopic
samples are listed in Table 1. The 3341.7 and 3430.7 cm-1 bands
exhibit H2O/D2O (1.3642 and 1.3425) and H216O/H218O frequency
ratios (1.0020 and 1.0042) that are characteristic of symmetric and
antisymmetric HOH stretching vibrations. The mixed H216O +
H218O (Figure 1, spectrum d) and H2O + HDO + D2O (Figure 1
of Supporting Information) spectra clearly show that one H2O unit
with two equivalent H atoms is involved in these two modes. The
strong H2O bending vibration overlaps the O-O stretching mode
of H2OOO+. Yet the corresponding modes of the D2OOO+ and
H2O18O18O isotopomers are observed distinctly at 1601.1 and
1502.2 cm-1 (Figure 2 of Supporting Information). This mode
shows small isotopic shifts with D2O and H218O. The mixed
16O2 + 18O2 and 16O2 + 16O18O + 18O2 spectra indicate that one
O2 unit with slightly nonequivalent O atoms is involved in this
mode. That the O-O stretching frequencies of H2O18O18O+ are
lower than those of D2O18O18O+ and HDO18O18O suggests that this
mode for the last two isotopomers is involved in anharmonic
resonance with a combination of lower-lying levels. The less
prominent 731.0 cm-1 band is assigned to the H2O-O2 stretching
vibration of the cation.
-
absorptions. Similarly, O3 (1039.4 cm-1), O3- (803.9 cm-1),15 O4
+
(953.6 cm-1),16 and O4 (1118.4 cm-1 17
)
were produced after
discharge of O2/Ar and condensation. New absorptions were
observed when H2O/Ar was co-deposited with discharged O2/Ar.
The same new absorptions were produced when H2O/Ar was
subjected to discharge and co-deposited with O2/Ar. These bands
can be grouped together by their consistent behavior upon annealing
and photolysis. The spectra in the O-H stretching frequency region
are shown in Figure 1. The new product absorptions diminished
after the sample was annealed to 20 K or after broadband Hg arc
lamp photolysis (Figure 1, spectrum b). When CCl4 was added to
serve as an electron trap,18 the intensities of the new product
absorptions were increased relative to the neutral H2O‚OH and HOO
-
-
absorptions (Figure 1, spectrum c), while the O3 and O4 anions
were eliminated. These results suggest that the new product is a
cationic species.
Isotopic substitutions (D2O, H218O, 18O2, and their mixtures) were
employed for product identification based on isotopic shifts and
After this H2OOO+ radical cation was fingerprinted spectro-
scopically, quantum chemical computations gave insight into the
† Fudan University.
‡ University of Georgia.
9
11512
J. AM. CHEM. SOC. 2003, 125, 11512-11513
10.1021/ja037125z CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
predicted by SVWN/6-311++G** may be more accurate than the
CCSD(T) and the other DFT distances, which may overestimated.
The overly long (2.296 Å) separation predicted by CASSCF(11,11)/
6-311G** evidently is due to the lack of dynamic electron
correlation. These problems - self-interaction error in DFT, large
spin contamination in CCSD(T), and lack of dynamic correlation
in CASSCF - might, in principle, be overcome at multireference
levels, such as MRSDCI and MRCI-SD/AQCC, but optimization
and frequency computations are not feasible at present.
In summary, we have characterized H2OOO+ to be a complex
involving a 3c-1e bond, instead of a simple ion-molecule
complex. The H2OOO+ cation is stable under visible irradiation; it
only was destroyed by UV photolysis. However, the cation
absorption diminished quickly on annealing, suggesting high
reactivity toward, for example, O2 or H2O.
Figure 2. (A) Geometries calculated at various levels (bond length in Å,
+
bond angle in deg). (B) Interaction between the πy* of O2 and in-plane
water lone pair. The values in parentheses are S2 values.
Table 2. Comparison of Calculated and Observed IR Frequencies
Acknowledgment. The NSFC (20125033), the NKBRSF, and
the University of Georgia supported this work. We thank Hans
Lischka for attempting multireference calculations, and H. F.
Schaefer, III and the referees for helpful discussions.
(in cm-1) for H2OOO+ (Values in Parentheses Are IR Intensities)
OH asy str.
OH sym. str.
O−O str.
H O−O str.
2 2
B3LYP
BHHLYP
BLYP
3723(238)
3861(320)
3587(206)
3615(211)
3624(271)
3836
3621(535)
3746(884)
3490(340)
3516(323)
3521(349)
3738
1762(593)
1860(1423)
1645(240)
1694(219)
1773(186)
1820
679(133)
687(109)
689(167)
711(169)
745(190)
647
Supporting Information Available: Spectra and calculated vibra-
tional frequencies and intensities (PDF). This material is available free
of charge via the Internet at http://pubs.acs.org.
BP86
SVWN
CCSD(T)
observed
3430.7
3341.7
1601.1a
731.0
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hybrid B3LYP (679 cm-1) and BHHLYP (687 cm-1) values are
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S2 ) 1.68 value for the doublet is quite large. Surprisingly, the
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