Infrared spectroscopic and density functional theory study on the reactions of rhodium and cobalt atoms with carbon dioxide in rare-gas matrixes

Article abstract of DOI:10.1021/jp0728095

Reactions of laser-ablated rhodium and cobalt atoms with carbon dioxide molecules in solid argon and neon have been investigated using matrix isolation infrared spectroscopy. The OMCO, O₂MCO, OMCO^-(M = Rh, Co), OCo₂CO, and

Full text of DOI:10.1021/jp0728095

J. Phys. Chem. A 2007, 111, 7793-7799
7793
Infrared Spectroscopic and Density Functional Theory Study on the Reactions of Rhodium
and Cobalt Atoms with Carbon Dioxide in Rare-Gas Matrixes
Ling Jiang, Yun-Lei Teng, and Qiang Xu*
National Institute of AdVanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan, and
Graduate School of Science and Technology, Kobe UniVersity, Nada Ku, Kobe, Hyogo 657-8501, Japan
ReceiVed: April 11, 2007; In Final Form: May 31, 2007
Reactions of laser-ablated rhodium and cobalt atoms with carbon dioxide molecules in solid argon and neon
have been investigated using matrix isolation infrared spectroscopy. The OMCO, O2MCO, OMCO- (M )
Rh, Co), OCo2CO, and OCoCO+ molecules have been formed and characterized on the basis of isotopic
shifts, mixed isotopic splitting patterns, ultraviolet irradiation, CCl4-doping experiments, and the change of
laser power. Density functional theory calculations have been performed on these products. The overall
agreement between the experimental and calculated vibrational frequencies, relative absorption intensities,
and isotopic shifts supports the identification of these products from the matrix infrared spectrum.
Introduction
the OMCO, O2MCO, OMCO- (M ) Rh, Co), OCo2CO, and
OCoCO+ molecules.
The interaction of metals with carbon dioxide is of consider-
able interest because of its importance in a great number of
catalytic processes.1-8 Metal-catalyzed activation of carbon
dioxide has many potential incentives with economic and
environmental benefits.1-8 Extensive efforts have been made
to recycle CO2 from industrial emissions and to remove some
of this greenhouse gas.1-8 Transition metal catalysts have been
widely used in such processes. The dissociation of CO2 on
supported rhodium catalyst has been detected by infrared
spectroscopy above 523 K.9 Furthermore, the addition of Pt,
Pd, or Rh exhibited a significant promotion for the reforming
of CH4 with CO2 over Ni0.03Mg0.970 solid solution catalyst.10
Experimental and Theoretical Methods
The experiment for laser ablation and matrix isolation infrared
spectroscopy is similar to those previously reported.37,38 In short,
the Nd:YAG laser fundamental (1064 nm, 10 Hz repetition rate
with 10 ns pulse width) was focused on rotating Rh and Co
targets. Laser-ablated Rh and Co atoms were codeposited with
CO2 in excess argon (or neon) onto a CsI window cooled
normally to 4 K by means of a closed-cycle helium refrigerator.
Typically, 1-20 mJ/pulse laser power was used. CO2 (99.99%,
Takachiho Chemical Industrial Co., Ltd.), 13C16O2 (99%, 18O
< 1%, Cambridge Isotopic Laboratories), 12C18O2 (95%,
Cambridge Isotopic Laboratories), 12C16O2
+
13C16O2, and
Reactions of metal atoms with carbon dioxide have been
investigated, and a series of metal-carbon dioxide complexes
have been experimentally characterized.11-31 Quantum chemical
calculations have been performed to understand the electronic
structures and bonding characteristics of these complexes.11-34
The insertion product (OMCO) has been observed for all first-
row transition metal atoms except Cu and Zn in rare-gas
matrixes.15-23 The reactions of Cr through Cu atoms with CO2
give OMCO- anions, and Co, Ni, and Cu atoms also produce
12C16O2 12C18O2 were used in different experiments. In
+
general, matrix samples were deposited for 30-60 min with a
typical rate of 2-4 mmol/h. After sample deposition, IR spectra
were recorded on a Bio-Rad FTS-6000e spectrometer at 0.5
cm-1 resolution using a liquid nitrogen cooled HgCdTe (MCT)
detector for the spectral range of 5000-400 cm-1. Samples were
annealed at different temperatures and subjected to broad-band
irradiation for 10-15 min using a high-pressure mercury arc
lamp (Ushio, 100 W, λ > 250 nm).
additional MCO2 anions.15-23
-
Recent studies have shown that, with the aid of isotopic
substitution technique, matrix isolation infrared spectroscopy
combined with quantum chemical calculation is very powerful
in investigating the spectrum, structure, and bonding of novel
species.35,36 In contrast to extensive experimental and theoretical
studies of the interactions of CO2 molecules with the transition
metal and main group element atoms,11-31 however, much less
work has been done on the Rh + CO2 reactions. Recently, argon
matrix investigations of the reactions of laser-ablated Co metal
atoms with CO2 molecules have characterized the OCoCO,
OCoCO-, and CoCO2- molecules.23 Here we report a study of
reactions of laser-ablated rhodium and cobalt atoms with carbon
dioxide in solid argon and neon. IR spectroscopy coupled with
theoretical calculations provides evidence for the formation of
Density functional theory (DFT) calculations were performed
to predict the structures and vibrational frequencies of the
observed reaction products using the Gaussian 03 program.39
The BP86 density functional method was used.40 The 6-311+G(d)
basis set was used for the C and O atoms,41 and the Los Alamos
ECP plus DZ (LANL2DZ) basis set was for the Rh and Co
atoms.42 Geometries were fully optimized, and vibrational
frequencies were calculated with analytical second derivatives.
Previous investigations have shown that such computational
methods can provide reliable information for metal complexes,
such as infrared frequencies, relative absorption intensities, and
isotopic shifts.11-38
Results and Discussion
Experiments have been done with carbon dioxide concentra-
tions ranging from 0.02% to 2.0% in excess argon and neon.
* Corresponding author. E-mail: q.xu@aist.go.jp.
10.1021/jp0728095 CCC: $37.00 © 2007 American Chemical Society
Published on Web 07/24/2007

7794 J. Phys. Chem. A, Vol. 111, No. 32, 2007
Jiang et al.
Figure 1. Infrared spectra in the 2200-1900 and 800-700 cm-1
regions from codeposition of laser-ablated Rh atoms with 1.0% CO2
in Ar. (a) After 1 h of sample deposition at 4 K, (b) after annealing to
25 K, (c) after 10 min of broad-band irradiation, and (d) after annealing
to 30 K.
Figure 3. Infrared spectra in the 2150-1800 cm-1 region from
codeposition of laser-ablated Rh atoms with 0.3% CO2 in Ne. (a) After
45 min of sample deposition at 4 K, (b) after annealing to 10 K, (c)
after 12 min of broad-band irradiation, (d) after annealing to 12 K,
and (e) 0.3% CO2 + 0.05% CCl4, after annealing to 10 K.
Figure 2. Infrared spectra in the 2050-1950 cm-1 region for laser-
ablated Rh atoms codeposited with isotopic CO2 in Ar after annealing
to 25 K. (a) 1.0% 12C16O2, (b) 0.7% 12C16O2 + 0.7% 13C16O2, (c) 1.0%
13C16O2, (d) 0.7% 12C16O2 + 0.7% 12C18O2, and (e) 1.0% 12C18O2.
Figure 4. Infrared spectra in the 2150-1800 cm-1 region from
codeposition of laser-ablated Rh atoms with 0.2% 12C16O2 + 0.2%
12C18O2 in Ne. (a) After 45 min of sample deposition at 4 K, (b) after
annealing to 10 K, (c) after 12 min of broad-band irradiation, and (d)
after annealing to 12 K.
The experiments of the Co atoms with CO2 in the argon matrix
have been reported previously23 and will not be shown in the
present study. Typical infrared spectra for the reactions of laser-
ablated Rh atoms with CO2 molecules in excess argon and neon
in the selected regions are illustrated in Figures 1-4, and those
for the reactions of laser-ablated Co atoms with CO2 molecules
in excess neon in the selected regions are illustrated in Figures
5-7. The absorption bands in different isotopic experiments
are listed in Tables 1 and 2. The stepwise annealing and
irradiation behavior of the product absorptions is also shown
in the figures and will be discussed below. Experiments were
also done with different concentrations of CCl4 serving as an
possible reaction products. The comparison of the observed and
calculated isotopic frequency ratios for the C-O and M-O (M
) Rh, Co) stretching modes of the products is summarized in
Table 3. The ground electronic states, point groups, vibrational
frequencies, and intensities are listed in Table 4.
ORhCO. In the reaction of the Rh atoms with CO2 in the
argon matrix, two absorptions at 2024.2 and 779.2 cm-1 appear
together during sample deposition, change little after annealing
to 25 K, increase visibly after broad-band irradiation, and
increase slightly after further annealing to higher temperature
(Table 1 and Figure 1). The upper band at 2024.2 cm-1 shifts
to 1977.4 cm-1 with 13C16O2 and to 1979.7 cm-1 with 12C18O2,
exhibiting isotopic frequency ratios (12C16O2/13C16O2, 1.0237;
12C16O2/12C18O2, 1.0225) characteristic of C-O stretching
vibrations. The mixed 12C16O2 + 13C16O2 and 12C16O2 + 12C18O2
isotopic spectra (Figure 2) only provide the sum of pure isotopic
bands, which indicates only one CO unit is involved in this
carbonyl stretching mode.50 The 779.2 cm-1 band shows no
electron scavenger. The absorptions of the RhO, (RhO)x,43
- 45-49
CoO,44 CO, CO4-, and C2O4
molecules have also been
observed in the present experiments and will not be discussed
here. It is noted that the (RhO)x absorptions increase sharply
and new absorptions increase slightly with the increase of the
laser power in the Rh + CO2 reaction, suggesting that these
new absorptions involve one Rh atom other than Rhx.
Quantum chemical calculations have been carried out for the
possible isomers and electronic states of the potential product
molecules. Figure 8 shows the optimized structures of the

Reactions of Rh and Co with CO2 in Rare Gases
J. Phys. Chem. A, Vol. 111, No. 32, 2007 7795
Figure 7. Infrared spectra in the 2100-1800 cm-1 region from
codeposition of laser-ablated Co atoms with 0.3% 12C16O2 + 0.3%
13C16O2 in Ne. (a) After 45 min of sample deposition at 4 K, (b) after
annealing to 10 K, (c) after 12 min of broad-band irradiation, and (d)
after annealing to 11 K.
Figure 5. Infrared spectra in the 2100-1800 cm-1 region from
codeposition of laser-ablated Co atoms with 0.4% CO2 in Ne. (a) After
45 min of sample deposition at 4 K, (b) after annealing to 10 K, (c)
after 12 min of broad-band irradiation, (d) after annealing to 11 K,
and (e) 0.3% CO2 + 0.05% CCl4, after 12 min of broad-band irradiation
and annealing to 11 K.
4
which lies 4 kcal/mol lower in energy than a A′ one. For the
C-O stretching mode, the vibrational frequency is calculated
to be 2019.7 cm-1 with the 12C16O2/13C16O2 and 12C16O2/12C18O2
isotopic frequency ratios of 1.0245 and 1.0221 (Tables 3 and
4), respectively, which are in agreement with the experimental
observations. The Rh-O stretching vibration is predicted to be
776.3 cm-1, and the calculated 12C16O2/12C18O2 isotopic fre-
quency ratio of 1.0526 is consistent with the experimental value
of 1.0528 (Table 3). These agreements support the assignment
of the ORhCO molecule.
O2RhCO. In the reaction of the Rh atoms with CO2 in the
neon matrix, the absorption at 2096.7 cm-1 appears weakly
during sample deposition, changes little after annealing to 10
K, increases sharply after broad-band irradiation, and increases
slightly after further annealing to 12 K (Table 1 and Figure 3).
This band shifts to 2049.2 cm-1 with 13C16O2 and to 2049.4
cm-1 with 12C18O2, exhibiting isotopic frequency ratios (12C16O2/
13C16O2, 1.0232; 12C16O2/12C18O2, 1.0231) characteristic of C-O
stretching vibrations. The mixed 12C16O2 + 12C18O2 isotopic
spectra (Figure 4) only provide the sum of pure isotopic bands,
which indicates that only one CO unit is involved in this
carbonyl stretching mode.50
DFT calculations for the O2RhCO molecule provide the C-O
stretching vibrational frequency at 2073.0 cm-1 (583 km/mol)
with calculated 12C16O2/13C16O2 and 12C16O2/12C18O2 ratios in
accord with the experimental values (Tables 1, 3, and 4). The
antisymmetric O-Rh-O stretching vibrational frequency is
calculated at 847.3 cm-1, which has a relatively small intensity
(123 km/mol) and is not readily observed, consistent with the
absence from the present experiments. The corresponding C-O
stretching frequency of the O2RhCO molecule in solid argon
appears at 2093.8 cm-1 (Table 1 and Figure 1).
Figure 6. Infrared spectra in the 1000-700 cm-1 region from
codeposition of laser-ablated Co atoms with 0.4% CO2 in Ne. (a) After
45 min of sample deposition at 4 K, (b) after annealing to 10 K, (c)
after 12 min of broad-band irradiation, (d) after annealing to 11 K,
and (e) 0.3% CO2 + 0.05% CCl4, after 12 min of broad-band irradiation
and annealing to 11 K.
carbon isotopic shift, but shifts to 740.1 cm-1 with 12C18O2.
The 12C16O2/12C18O2 isotopic frequency ratio of 1.0528 is very
close to the diatomic Rh16O/Rh18O frequency ratio of 1.0516,43
suggesting a Rh-O stretching mode. Only doublets have been
observed in the 12C16O2 + 12C18O2 isotopic spectra. Furthermore,
doping with CCl4 has no effect on these bands (not shown here),
suggesting that the product is neutral.51 The 2024.2 and 779.2
cm-1 bands are therefore assigned to the C-O and Rh-O
stretching vibrations of the neutral ORhCO molecule, respec-
tively. The corresponding C-O and Rh-O stretching frequen-
cies of ORhCO in solid neon appear at 2045.0 and 790.1 cm-1
(Table 1 and Figure 3), respectively, which are 20.8 and 10.9
cm-1 blue-shifted from the argon matrix counterpart.
ORhCO-. In the reaction of Rh atoms with CO2 in the neon
matrix, the absorption at 1867.8 cm-1 appears weakly during
sample deposition, changes little after annealing to 10 K,
disappears after broad-band irradiation, and does not return after
further annealing to 12 K (Table 1 and Figure 3). This band
shifts to 1823.8 cm-1 with 13C16O2 and to 1828.9 cm-1 with
12C18O2, exhibiting isotopic frequency ratios (12C16O2/13C16O2,
1.0241; 12C16O2/12C18O2, 1.0213) characteristic of C-O stretch-
ing vibrations. The mixed 12C16O2 + 12C18O2 isotopic spectra
BP86 calculations predict that the ORhCO molecule has a
2
Cs symmetry with a A′′ ground state (Table 4 and Figure 8),

7796 J. Phys. Chem. A, Vol. 111, No. 32, 2007
Jiang et al.
TABLE 1: IR Absorptions (in cm-1) Observed from Codeposition of Laser-Ablated Rh Atoms with CO2 in Excess Argon and
Neon at 4 K
12C16O2
13C16O2
12C18O2
R(12/13)
R(16/18)
assignment
Ar
2093.8
2024.2
799.0
779.2
720.9
2043.1
1977.4
799.0
779.2
720.9
2043.2
1979.7
759.8
740.1
686.2
1.0248
1.0237
1.0000
1.0000
1.0000
1.0248
1.0225
1.0516
1.0528
1.0506
O2RhCO
ORhCO
RhO
ORhCO
(RhO)x
Ne
2096.7
2045.0
1872.8
1867.8
819.9
2049.2
1998.6
1833.0
1823.8
819.9
2049.4
1999.8
1840.3
1828.9
781.3
1.0232
1.0232
1.0217
1.0241
1.0000
1.0000
1.0231
1.0226
1.0177
1.0213
1.0494
1.0530
O2RhCO
ORhCO
?
ORhCO-
RhO
790.1
790.1
750.3
ORhCO
TABLE 2: IR Absorptions (in cm-1) Observed from Codeposition of Laser-Ablated Co Atoms with CO2 in Excess Neon at 4 K
12C16O2
13C16O2
12C18O2
R(12/13)
R(16/18)
assignment
2102.2
2040.4
2027.1
1995.7
1801.3
942.9
853.7
793.3
753.9
2054.6
1994.7
1981.2
1949.2
1759.4
942.9
853.7
793.3
753.9
2054.5
1993.5
1981.2
1951.9
1758.5
905.6
816.1
758.2
720.9
1.0232
1.0229
1.0232
1.0239
1.0238
1.0000
1.0000
1.0000
1.0000
1.0232
1.0235
1.0232
1.0224
1.0243
1.0412
1.0461
1.0463
1.0458
O2CoCO
OCoCO+
OCoCO
OCo2CO
OCoCO-
O2CoCO
CoO
OCoCO
OCoCO-
TABLE 3: Comparison of Observed (in Neon) and Calculated IR Frequency Ratios for the Products
R(12/13)
R(16/18)
species
vibrational mode
obsd
calcd
obsd
calcd
ORhCO
νC-O
νRh-O
νC-O
νC-O
νC-O
νCo-O
νC-O
νCo-O
νC-O
νC-O
νCo-O
νC-O
1.0232
1.0000
1.0232
1.0241
1.0232
1.0000
1.0232
1.0000
1.0239
1.0238
1.0000
1.0229
1.0245
1.0004
1.0239
1.0247
1.0238
1.0000
1.0240
1.0001
1.0241
1.0248
1.0000
1.0235
1.0226
1.0528
1.0231
1.0213
1.0232
1.0463
1.0232
1.0412
1.0224
1.0243
1.0458
1.0235
1.0221
1.0526
1.0230
1.0217
1.0233
1.0460
1.0228
1.0404
1.0227
1.0217
1.0451
1.0235
O2RhCO
ORhCO-
OCoCO
O2CoCO
OCo2CO
OCoCO-
OCoCO+
(Figure 4) only provide the sum of pure isotopic bands, which
indicates only one CO unit is involved in this carbonyl stretching
mode.50 Furthermore, the 1867.8 cm-1 band disappears after
doping with CCl4 (Figure 3, trace e), suggesting that the product
is anionic.51 Accordingly, the 1867.8 cm-1 band is assigned to
the C-O stretching vibration of the ORhCO- anion. The argon
counterpart of ORhCO- is absent from the present matrix
experiments.
The present DFT calculations predict that the ORhCO-
3
molecule has a A′′ ground state with a Cs symmetry (Table 4
and Figure 8). The C-O stretching vibrational frequency is
calculated at 1842.9 cm-1 (1087 km/mol) (Table 4), which is
in agreement with the experimental value of 1867.8 cm-1 (Table
1). The Rh-O stretching vibration is predicted to be 671.6 cm-1
,
which has a relatively small intensity (77 km/mol) and is not
readily observed, consistent with the absence from the present
experiments. The RhCO angle in the anionic ORhCO-
molecule (163.6°) is slightly smaller than in the neutral ORhCO
molecule (173.7°) (Figure 8).
Other Absorption from the Rh + CO2 Reaction. In the
Rh + CO2 reaction in solid neon (Figure 3), a weak absorption
at 1872.8 cm-1 appears during sample deposition, increases
slightly after annealing to 10 K, decreases markedly after broad-
band irradiation, and recovers slightly after further annealing.
This band shifts to 1833.0 cm-1 with 13C16O2 and to 1840.3
cm-1 with 12C18O2, giving 12C16O2/13C16O2 and 12C16O2/12C18O2
isotopic frequency ratios of 1.0217 and 1.0177, which suggests
that this mode is not a pure C-O stretch mode. Tentatively,
Figure 8. Optimized structures (bond lengths in angstroms, bond angles
in degrees) of possible reaction products.

Reactions of Rh and Co with CO2 in Rare Gases
J. Phys. Chem. A, Vol. 111, No. 32, 2007 7797
TABLE 4: Ground Electronic States, Point Groups, Vibrational Frequencies (cm-1), and Intensities (km/mol) Calculated for
the Reaction Productsa
species
electronic state
point group
frequency (intensity, mode)
ORhCO
O2RhCO
ORhCO-
OCoCO
O2CoCO
OCo2CO
OCoCO-
OCoCO+
2A′′
2A′′
3A′′
4A′′
2A′′
3A′
Cs
Cs
Cs
Cs
Cs
Cs
Cs
Cs
2019.7 (663, A′), 776.3 (32, A′), 525.6 (9, A′), 428.0 (4, A′)
2073.0 (583, A′), 847.3 (123, A′′), 806.1 (6, A′), 463.5 (9, A′)
1842.9 (1087, A′), 671.6 (77, A′), 526.0 (3, A′), 421.3 (0.2, A′)
2025.2 (714, A′), 839.0 (46, A′), 474.7 (16, A′)
2108.5 (498, A′), 950.8 (114, A′′), 859.9 (3, A′), 511.9 (10, A′), 415.4 (1, A′)
1992.3 (1252, A′), 662.0 (21, A′), 544.4 (2, A′), 471.2 (48, A′), 449.7 (9, A′), 444.5 (3, A′′)
1839.0 (1177, A′), 781.2 (117, A′)
3A′′
3A′′
2186.8 (191, A′), 891.1 (16, A′), 424.2 (4, A′)
a Only the frequencies above 400 cm-1 are listed.
the band at 1872.8 cm-1 is assigned to the absorption of some
impurities.
increases visibly after broad-band irradiation, and changes little
after further annealing to 11 K (Table 2 and Figure 5). This
band shifts to 1949.2 cm-1 with 13C16O2 and to 1951.9 cm-1
with 12C18O2, exhibiting isotopic frequency ratios (12C16O2/
13C16O2, 1.0239; 12C16O2/12C18O2, 1.0224) characteristic of C-O
stretching vibrations. The mixed 12C16O2 + 13C16O2 isotopic
spectra (Figure 7) only provide the sum of pure isotopic bands,
which indicates that only one CO unit is involved in this
carbonyl stretching mode.50 It is noted that the 1995.7 cm-1
band is favored under the experimental conditions of higher
laser energy, indicating that this new absorption should involve
more than one Co atom. Doping with CCl4 has no effect on
this band (Figure 5e), suggesting that the product is neutral.51
BP86 calculations for the OCo2CO molecule provide the
C-O stretching vibrational frequency at 1992.3 cm-1 (Table 4
and Figure 8), which is in good agreement with the experimental
value of 1995.7 cm-1 (Table 1). The calculated 12C16O2/13C16O2
and 12C16O2/12C18O2 isotopic frequency ratios of 1.0241 and
1.0227 are consistent with the experimental values of 1.0239
and 1.0224, respectively (Table 3), which suggests the assign-
ment of the OCo2CO molecule. As listed in Table 4, the Co-O
and Co-C stretching vibrational frequencies of the OCo2CO
molecule are predicted to have relatively small intensities and
are not readily observed, in accord with the absence from the
present experiments. The argon counterpart of OCo2CO is absent
from the matrix experiments.23 In contrast, the C-O stretching
vibrational frequency of the Co2CO molecule has been observed
at 1953.3 cm-1 from the reactions of laser-ablated Co atoms
with CO molecules in solid argon.52
OCoCO+. In the reaction of Co atoms with CO2 in solid
neon, a sharp band at 2040.4 cm-1 appears during sample
deposition, and changes little after annealing to 10 K, after
broad-band irradiation, and after further annealing to 11 K
(Table 2 and Figure 5). This band shifts to 1994.7 cm-1 with
13C16O2 and to 1993.5 cm-1 with 12C18O2, exhibiting isotopic
frequency ratios (12C16O2/13C16O2, 1.0229; 12C16O2/12C18O2,
1.0235) characteristic of C-O stretching vibrations. The mixed
12C16O2 + 13C16O2 isotopic spectra (Figure 7) only provide the
sum of pure isotopic bands, which indicates only one CO unit
is involved in this carbonyl stretching mode.50 Furthermore, the
2040.4 cm-1 band increases markedly after doping with CCl4
(Figure 5e), suggesting that the product is cationic.51 Therefore
the cation with the OCoCO+ stoichiometry is considered.
DFT calculations predict the C-O stretching vibrational
frequencies of the OCoCO+, CoOCO+, and OCoOC+ molecules
to be 2186.8, 2404.7, and 1958.7 cm-1, respectively. The
OCoCO+ and OCoOC+ molecules lie 57 and 89 kcal/mol higher
in energy than the CoOCO+ molecule. However, the calculated
C-O stretching vibrational frequency in the CoOCO+ molecule
(2404.7 cm-1) is much higher than the experimental value of
2040.4 cm-1. Accordingly, the 2040.4 cm-1 band is assigned
to the C-O stretching vibration of the OCoCO+ cation. As listed
OCoCO, OCoCO-, and CoCO2-. The neon matrix absorp-
tions at 2027.1 and 793.3 cm-1 (Table 2 and Figures 5 and 6)
are due to the C-O and Co-O stretching vibrations of the
OCoCO molecule, respectively, which are consistent with the
previous reports of 2026.6 and 783.8 cm-1 absorptions in
argon.23 The 1801.3 and 753.9 cm-1 bands are due to the C-O
and Co-O stretching vibrations of the OCoCO- anion, respec-
tively. Weak absorptions at 1714.9, 1237.3, and 725.4 cm-1
are due to the antisymmetric C-O, symmetric C-O, and Co-C
-
stretching vibrations of the CoCO2 anion, respectively. Dis-
cussions about the OCoCO, OCoCO-, and CoCO2- molecules
in solid argon have been reported previously,23 and we will focus
on the new products from the reaction of the Co atoms with
CO2 in the neon matrix in this study.
O2CoCO. In the reaction of the Co atoms with CO2 in the
neon matrix, the absorptions at 2102.2 and 942.9 cm-1 appear
together during sample deposition, change little after annealing
to 10 K, increase visibly after broad-band irradiation, and
increase markedly after further annealing to higher temperature
(Table 2 and Figures 5 and 6). The 2102.2 cm-1 band shifts to
2054.6 cm-1 with 13C16O2 and to 2054.5 cm-1 with 12C18O2,
exhibiting isotopic frequency ratios (12C16O2/13C16O2, 1.0232;
12C16O2/12C18O2, 1.0232) characteristic of C-O stretching
vibrations. The mixed 12C16O2
+
13C16O2 isotopic spectra
(Figure 7) only provide the sum of pure isotopic bands, which
indicates only one CO unit is involved in this carbonyl stretching
mode.50 The 942.9 cm-1 band shows no carbon isotopic shift,
but shifts to 905.6 cm-1 with 12C18O2. The 12C16O2/12C18O2
isotopic frequency ratio of 1.0412 is lower than the CoO
diatomic harmonic ratio of 1.0465 (in argon),44 but is much
closer to the Co16O/Co18O ratio for the ν3 mode of the OCoO
molecule (1.0376, in argon).44 A triplet isotopic pattern has been
observed in the 12C16O2 + 12C18O2 isotopic spectra, suggesting
that an antisymmetric O-Co-O stretching mode is involved
in this product. Accordingly, the 2102.2 and 942.9 cm-1 bands
are assigned to the C-O stretching and antisymmetric O-Co-O
stretching vibrations of the O2CoCO molecule, respectively. The
argon counterpart of O2CoCO is absent from the matrix
experiments.23
BP86 calculations predict that the O2CoCO molecule has a
2
Cs symmetry with a A′′ ground state (Table 4 and Figure 8).
The C-O stretching and antisymmetric O-Co-O stretching
vibrational frequencies are calculated to be 2108.5 (498) and
950.8 cm-1 (114 km/mol) (Table 4), respectively, which are
consistent with the experimental observations. A similar agree-
ment has also been obtained for the 12C16O2/13C16O2 and
12C16O2/12C18O2 isotopic frequency ratios (Table 3).
OCo2CO. In the reaction of the Co atoms with CO2 in solid
neon, the absorption at 1995.7 cm-1 appears weakly during
sample deposition, changes little after annealing to 10 K,

7798 J. Phys. Chem. A, Vol. 111, No. 32, 2007
Jiang et al.
in Table 3, the calculated 12C16O2/13C16O2 and 12C16O2/12C18O2
isotopic frequency ratios of 1.0235 and 1.0235 are consistent
with the experimental values of 1.0229 and 1.0235, respectively.
The Co-O stretching vibration is predicted to be 891.1 cm-1
(Table 4), which has relatively small intensity (16 km/mol) and
is not readily observed, consistent with the absence from the
present experiments.
cm-1 in argon and 2045.0 and 790.1 cm-1 in neon are assigned
to the C-O and Rh-O stretching vibrations of the ORhCO
molecule, respectively. The O2RhCO and ORhCO- molecules
have also been observed in the rare-gas matrixes. Previous argon
matrix investigations of the reactions of laser-ablated Co metal
atoms with CO2 molecules have characterized the OCoCO,
OCoCO-, and CoCO2- molecules.23 Present neon experiments
produce new absorptions of the O2CoCO, OCo2CO, and
OCoCO+ molecules. Density functional theory calculations have
been performed on these products, which support the experi-
mental assignments of the infrared spectra.
Reaction Mechanism
On the basis of the behavior of sample annealing and
irradiation, together with the observed species and calculated
stable isomers, a plausible reaction mechanism can be proposed
as follows. Under the present experimental conditions, the
OMCO (M ) Rh, Co) molecules are the primary products
during sample deposition (Figures 1, 3, and 5), suggesting that
the spontaneous insertion of laser-ablated Rh and Co atoms into
CO2 to form the OMCO molecules is the dominant process
(reaction 1). Similar findings have also been found for the groups
3-10 transition metal atoms.15-23 Theoretical investigations
reveal that the insertion of metal atoms into CO2 to form the
OMCO molecules needs a low or no energy barrier:15-23,32,53
Acknowledgment. The authors would like to express thanks
to the reviewers for valuable suggestions. We gratefully
acknowledge financial support for this research by a Grant-in-
Aid for Scientific Research (B) (Grant 17350012) from the
Ministry of Education, Culture, Sports, Science and Technology
(MEXT) of Japan. L.J. thanks MEXT of Japan and Kobe
University for an Honors Scholarship.
References and Notes
(1) Palmer, D. A.; van Eldik, R. Chem. ReV. 1983, 83, 651.
(2) Culter, A. R.; Hanna, P. K.; Vites, J. C. Chem. ReV. 1988, 88, 1363.
(3) Jessop, P. G.; Ikariya, T.; Noyori, R. Chem. ReV. 1995, 95, 259.
(4) Freund, H. J.; Roberts, M. W. Surf. Sci. Rep. 1996, 25, 225.
(5) Gibson, D. H. Chem. ReV. 1996, 96, 2063.
(6) Gibson, D. H. Coord. Chem. ReV. 1999, 185-186, 335.
(7) Solymosi, F. J. Mol. Catal. 1991, 65, 337.
(8) Creutz, C. In Electrochemical and Electrocatalytic Reactions of
Carbon Dioxide; Sullivan, B. P., Krist, K., Guard, H. E., Eds.; Elsevier:
Amsterdam, 1993.
M + CO2 f OMCO
(M ) Rh, Co)
(1)
The observation of RhO, (RhO)x, CoO, and CO shows the
presence of the O atoms and the CO molecules. The decom-
position of the OMCO molecule may proceed by radiation
during sample deposition (reaction 2). The O2MCO molecule
may be formed from the reaction of the OMCO molecule with
the O atom (reaction 3) or with another CO2 molecule (reactions
4 and 5). Under the experimental conditions of higher laser
energy, the OCo2CO molecule is generated by the addition of
the Co atom to the OCoCO molecule (reaction 6):
(9) Erdohelyi, A.; Cserenyi, J.; Solymosi, F. J. Catal. 1993, 144, 287.
(10) Chen, Y. G.; Tomishige, K.; Yokoyama, K.; Fujimoto, K. Appl.
Catal., A 1997, 165, 335.
(11) Kafafi, Z. H.; Hauge, R. H.; Billups, W. E.; Margrave, J. L. J. Am.
Chem. Soc. 1983, 105, 3886 (Li + CO2).
(12) Kafafi, Z. H.; Hauge, R. H.; Billups, W. E.; Margrave, J. L. Inorg.
Chem. 1984, 23, 177 (Cs + CO2).
OMCO f MO + CO
(2)
(3)
(13) Andrews, L.; Tague, T. J., Jr. J. Am. Chem. Soc. 1998, 120, 13230
(Be + CO2).
OMCO + O f O2MCO
(14) Solov’ev, V. N.; Polikarpov, E. V.; Nemukhin, A. V.; Sergeev, G.
B. J. Phys. Chem. A 1999, 103, 6721 (Mg + CO2).
(15) Zhou, M. F.; Andrews, L. J. Am. Chem. Soc. 1998, 120, 13230
(Sc, Y + CO2).
MO + CO2 f O2MCO
OMCO + CO2 f O2MCO + CO
OCoCO + Co f OCo2CO
(4)
(5)
(6)
(16) Mascetti, J.; Tranquille, M. J. Phys. Chem. 1988, 92, 2177; Coord.
Chem. ReV. 1999, 190-192, 557 (Ti, V, Cr, Fe, Co, Ni, Cu + CO2).
(17) Chertihin, G. V.; Andrews, L. J. Am. Chem. Soc. 1995, 117, 1595
(Ti + CO2).
(18) Zhou, M. F.; Andrews, L. J. Phys. Chem. A 1999, 103, 2066 (Ti,
V + CO2).
Recent investigations have shown that laser ablation of metal
targets produces not only neutral metal atoms, but also metal
cations and electrons, and ionic metal complexes can also be
formed in the reactions with small molecules.51 In the present
experiments, the OMCO- anion appears during sample deposi-
tion and changes little after sample annealing (Figure 3),
suggesting that this anion may be generated by electron capture
by neutral OMCO during codeposition (reaction 7). In addition,
the OCoCO+ molecule may be formed from the reaction of the
Co+ cation with CO2 (reaction 8):
(19) Zhang, L.; Wang, X.; Chen, M.; Qin, Q. Z. Chem. Phys. 2000,
254, 231 (Zr + CO2).
(20) Chen, M.; Wang, X.; Zhang, L.; Qin, Q. Z. J. Phys. Chem. A 2000,
104, 7010 (Nb + CO2).
(21) Wang, X.; Chen, M.; Zhang, L.; Qin, Q. Z. J. Phys. Chem. A 2000,
104, 758 (Ta + CO2).
(22) Souter, P. F.; Andrews, L. Chem. Commun. 1997, 777; J. Am. Chem.
Soc. 1997, 119, 7350 (Cr, Mo, W + CO2).
(23) Zhou, M. F.; Liang, B.; Andrews, L. J. Phys. Chem. A 1999, 103,
2013 (Cr-Zn + CO2).
(24) Liang, B.; Andrews, L. J. Phys. Chem. A 2002, 106, 595 (Re +
CO2).
(25) Liang, B.; Andrews, L. J. Phys. Chem. A 2002, 106, 4042 (Os, Ru
+ CO2).
OMCO + e- f OMCO-
Co+ + CO2 f OCoCO+
(7)
(8)
(26) Andrews, L.; Zhou, M. F.; Liang, B.; Li, J.; Bursten, B. E. J. Am.
Chem. Soc. 2000, 122, 11440 (U, Th + CO2).
(27) Bulkholder, T. R.; Andrews, L.; Bartlett, R. J. J. Phys. Chem. 1993,
97, 3500 (B + CO2).
(28) Quere, A. M. L.; Xu, C.; Manceron, L. J. Phys. Chem. 1991, 95,
3031 (Al + CO2).
Conclusions
Reactions of laser-ablated Rh and Co atoms with CO2
molecules in solid argon and neon have been investigated using
matrix isolation infrared spectroscopy. On the basis of isotopic
shifts, mixed isotopic splitting patterns, ultraviolet irradiation,
and CCl4-doping experiments, absorptions at 2024.2 and 779.2
(29) Brock, L. R.; Duncan, M. A. J. Phys. Chem. 1991, 95, 3031 (Al +
CO2).
(30) Howard, J. A.; McCague, C.; Sutcliffe, R.; Tse, J. S.; Joly, H. A.
J. Chem. Soc., Faraday Trans. 1995, 91, 799 (Al, Ga + CO2).
(31) Himmel, H. J.; Downs, A. J.; Greene, T. M. Chem. ReV. 2002,
102, 4191, and references therein.

Reactions of Rh and Co with CO2 in Rare Gases
J. Phys. Chem. A, Vol. 111, No. 32, 2007 7799
(32) Papai, I.; Mascetti, J.; Fournier, R. J. Phys. Chem. A 1997, 101,
4465.
(33) Fan, H. J.; Liu, C. W. Chem. Phys. Lett. 1999, 300, 351.
(34) Sodupe, M.; Branchadell, V.; Rosi, M.; Bauschlicher, C. W., Jr. J.
Phys. Chem. A 1997, 101, 7854.
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,
revision B.04; Gaussian, Inc.: Pittsburgh, PA, 2003.
(40) Becke, A. D. Phys. ReV. A 1988, 38, 3098. Perdew, J. P. Phys.
ReV. B 1986, 33, 8822.
(35) See, for example: Xu, C.; Manceron, L.; Perchard, J. P. J. Chem.
Soc., Faraday Trans. 1993, 89, 1291. Bondybey, V. E.; Smith, A. M.;
Agreiter, J. Chem. ReV. 1996, 96, 2113. Fedrigo, S.; Haslett, T. L.;
Moskovits, M. J. Am. Chem. Soc. 1996, 118, 5083. Khriachtchev, L.;
Pettersson, M.; Runeberg, N.; Lundell, J.; Rasanen, M. Nature 2000, 406,
874. Himmel, H. J.; Manceron, L.; Downs, A. J.; Pullumbi, P. J. Am. Chem.
Soc. 2002, 124, 4448. Li, J.; Bursten, B. E.; Liang, B.; Andrews, L. Science
2002, 295, 2242. Andrews, L.; Wang, X. Science 2003, 299, 2049.
(36) Zhou, M. F.; Tsumori, N.; Li, Z.; Fan, K.; Andrews, L.; Xu, Q. J.
Am. Chem. Soc. 2002, 124, 12936. Zhou, M. F.; Xu, Q.; Wang, Z.; von
Rague´ Schleyer, P. J. Am. Chem. Soc. 2002, 124, 14854. Jiang, L.; Xu, Q.
J. Am. Chem. Soc. 2005, 127, 42. Xu, Q.; Jiang, L.; Tsumori, N. Angew.
Chem., Int. Ed. 2005, 44, 4338. Jiang, L.; Xu, Q. J. Am. Chem. Soc. 2005,
127, 8906.
(37) Burkholder, T. R.; Andrews, L. J. Chem. Phys. 1991, 95, 8697.
(38) Zhou, M. F.; Tsumori, N.; Andrews, L.; Xu, Q. J. Phys. Chem. A
2003, 107, 2458. Jiang, L.; Xu, Q. J. Chem. Phys. 2005, 122, 034505.
(39) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.;
Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
(41) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639.
Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980,
72, 650.
(42) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(43) Citra, A.; Andrews, L. J. Phys. Chem. A 1999, 103, 4845 (Rh +
O2).
(44) Chertihin, G. V.; Citra, A.; Andrews, L.; Bauschlicher, C. W., Jr.
J. Phys. Chem. A 1997, 101, 8793 (Co + O2).
(45) Jacox, M. E.; Milligan, D. E. J. Chem. Phys. 1971, 54, 3935.
(46) Jacox, M. E.; Thompson, W. E. J. Chem. Phys. 1989, 91, 1410.
(47) Zhou, M. F.; Andrews, L. J. Chem. Phys. 1999, 110, 2414.
(48) Zhou, M. F.; Andrews, L. J. Chem. Phys. 1999, 110, 6820.
(49) Zhou, M. F.; Zhang, L. N.; Chen, M. H.; Qin, Q. Z. J. Chem. Phys.
2000, 112, 7089.
(50) Darling, J. H.; Ogden, J. S. J. Chem. Soc., Dalton Trans. 1972,
2496.
(51) Zhou, M. F.; Andrews, L.; Bauschlicher, C. W., Jr. Chem. ReV.
2001, 101, 1931.
(52) Tremblay, B.; Manceron, L.; Gutsev, G.; Andrews, L.; Partridge,
H., III. J. Chem. Phys. 2002, 117, 8479.
(53) See, for example: Mebel, A. M.; Hwang, D. Y. J. Phys. Chem. A
2000, 104, 11662. Hwang, D. Y.; Mebel, A. M. J. Chem. Phys. 2002, 116,
5633.