Depletion kinetics of nickel atoms by sulfur dioxide

Article abstract of DOI:10.1021/jp983594p

The gas-phase depletion kinetics of Ni(a³F_J, a³D_J) in the presence of SO₂ are reported. Nickel atoms were produced by the 248 nm photodissociation of nickelocene and detected by laser-induced fluorescence. The ground term of Ni, a³F₄, and the two lowest energy spin-orbit states, a³D₃ and a³D₂, were found to react termolecularly (and with identical rate constants) with SO₂, an indication of rapid interconversion between these states. The limiting low-pressure third-order rate constant, measured over the temperature range 296-612 K, can be expressed as k_o(T) = 7.455-24.41(log T) + 3.993(log T)² cm⁶ molecule^-2 s^-1. A binding energy of 47 kcal mol^-1 was estimated by combining the kinetic results with unimolecular rate theory and density functional methods. The limiting high-pressure second-order rate constant over the temperature range is on the order of the collision rate. The other spin-orbit states of both terms depleted quite rapidly in the presence of SO₂, with rate constants also on the order of the collision rate.

Full text of DOI:10.1021/jp983594p

J. Phys. Chem. A 1999, 103, 75-79
75
Depletion Kinetics of Nickel Atoms by Sulfur Dioxide
Roy E. McClean
Chemistry Department, United States NaVal Academy, Annapolis, Maryland 21402
ReceiVed: September 3, 1998; In Final Form: October 22, 1998
The gas-phase depletion kinetics of Ni(a3F
, a D
3
are reported. Nickel atoms were
J
J
) in the presence of SO
2
produced by the 248 nm photodissociation of nickelocene and detected by laser-induced fluorescence. The
3
3
3
ground term of Ni, a F
termolecularly (and with identical rate constants) with SO
these states. The limiting low-pressure third-order rate constant, measured over the temperature range 296-
4
, and the two lowest energy spin-orbit states, a D
3 2
and a D , were found to react
2
, an indication of rapid interconversion between
2
6
-2 -1
6
o
12 K, can be expressed as k (T) ) 7.455-24.41(log T) + 3.993(log T) cm molecule s . A binding
-
1
energy of 47 kcal mol was estimated by combining the kinetic results with unimolecular rate theory and
density functional methods. The limiting high-pressure second-order rate constant over the temperature range
is on the order of the collision rate. The other spin-orbit states of both terms depleted quite rapidly in the
2
presence of SO , with rate constants also on the order of the collision rate.
TABLE 1: Atomic States of Ni and LIF Informationa
Introduction
There have been several recent investigations of bimolecular
Ni stateb
energy (cm-1
)
λ (nm) of excitationc
1
-5
3
reactions of transition-metal (TM) atoms with SO2.
These
a F
4
3
2
0
343.728
346.750
348.377
341.476
349.296
345.846
3
a F
1332.153
2216.519
204.786
879.813
1713.080
reactions are of interest, in part, because of the importance of
SO2 in acid rain and in the corrosion of metals. Many of the
gas-phase reactions have been observed to proceed with little
or no barriers. In most cases, the relatively fast rates have been
attributed to an electron-transfer mechanism whereby an electron
is transferred from the TM atom to the SO2. Due to the relatively
large ionization energies of TM atoms, valence interactions are
expected to play a role in their reactions; i.e., the reactions are
driven not only by an electron transfer, but also by the type of
orbital occupancies of the TM atoms.
3
a F
3
a D
3
2
1
3
a D
3
a D
a
The detection filter was centered at 350 nm and had fwhm ) 10
nm. b Reference 11. c Reference 12.
(argon), diluted precursor, and SO2 passed through separate mass
flow controllers after which they combined into one line and
entered the reaction chamber. A slow flow of argon passed over
the windows in order to minimize the deposition of the precursor
and photofragments. Total flows were between 150 and 8500
sccm, depending on the total pressure. Partial pressures of the
individual components were determined by their relative flows
and the total pressure in the reaction chamber. Pressures were
measured by Baratron manometers, and temperatures were
measured with a thermocouple attached to the reaction chamber.
Nickel atoms were produced from Ni(C5H5)2 by the unfocused
output of an excimer laser operating on KrF (248 nm) at 21
Hz. Rate-constant measurements did not depend on the pho-
3
3
In this paper, the depletion of Ni(a FJ, a DJ) by SO2 is
reported. Unlike the previous work on TM + SO2 reactions
where abstraction mechanisms were indicated, an abstraction
reaction is not thermodynamically feasible for the ground state
of Ni. The Ni + SO2 reaction is endothermic at relatively low
temperatures6,7 and, therefore, a termolecular mechanism is the
only viable reaction channel at room temperature. This work
provides information on the efficiency of 1:1 adduct formation
between Ni and SO2. It also allows one to determine if the Ni
excited states deplete at appreciable rates in the presence of
SO2, as observed in other TM + SO2 systems. Density
-
2
tolysis fluences, which were approximately 200-400 mJ cm
8
9
in the reaction chamber. Detection of nickel atoms was by LIF
using laser light from an excimer-pumped dye module. The
photolysis and dye beams counterpropagated through the
chamber. Neutral density filters were used to ensure that the
dye laser fluence (less than 1 mJ/pulse) did not affect the kinetic
results. The Ni states studied and the corresponding excitation
functional theory (DFT) and Troe’s factorization method are
combined with the kinetic results to estimate the binding energy
of the NiSO2 adduct.
Experimental Section
1
1,12
Details of the experimental arrangement have been described
wavelengths are listed in Table 1.
A photomultiplier tube
10
in detail elsewhere and are only summarized here. The laser-
photolysis/laser-induced fluorescence (LP/LIF), slow-flow tech-
nique was used in this work. The reaction chamber was a
stainless steel cross with gas inlet and outlet ports, a viewport
for LIF detection, and windows for passage of the laser beams;
the chamber was contained in a convection oven capable of
attaining temperatures up to 628 K. Nickelocene, the nickel
precursor, was entrained in a flow of argon gas. The buffer gas
and lens focusing system, situated 90° to the laser beams,
collected the LIF signal, which was subsequently sent to a gated
boxcar sampling module, and the boxcar’s output was stored
and analyzed by a computer.
All kinetic results are based on the disappearance of Ni atoms
under pseudo-first-order conditions, where the number density
of Ni was much less than the number density of SO2 and Ar.
Reaction time was taken as the delay time between the laser
1
0.1021/jp983594p CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/10/1998

76
J. Phys. Chem. A, Vol. 103, No. 1, 1999
McClean
Figure 2. Typical plot for determining second-order rate constants.
The conditions are the same as in Figure 1, except the partial pressures
of SO2 are changing. Each point represents an average of 2-3
2
Figure 1. Typical decay profile of Ni in the presence of SO . Data
3
are for Ni(a D .). T ) 296 K, Ptot ) 40 Torr, PSO2 ) 16.8 mTorr. The
3
-
11
3
measurements. The slope gives k ) (2.40 ( 0.06) × 10
cm
solid line through the data is an exponential fit with τ ) 68.0 µs. The
-1 -1
molecule
s , where the uncertainty is (2σ from the linear regression.
inset is the same data in semilogarithmic form; note the linearity.
TABLE 2: Measured Second-Order Rate Constants for the
pulses. For a given experimental run, the delay time was varied
by a digital delay generator controlled by a computer. Minimum
delay times were typically 1-10 µs in order to prevent overlap
of the prompt emission with the LIF signal. The trigger source
for these experiments was scattered pump laser light incident
upon a fast photodiode. LIF decay traces consisted of 200-
3
3
a
Depletion of Ni (a F
J
, a D
J
) by SO
2
k (10- cm molecule s-1
11
3
-1
)
state
P (Torr)
296 K
349 K
399 K
498 K
612 K
a3F
10
20
0.760
1.39
4.83
17.9
15.5
0.799
1.49
2.40
3.82
4.63
5.79
6.79
8.27
8.97
9.32
0.793
2.19
13.2
4
0.494
2.41
1
20
10
10
10
20
40
5
00 points, each point averaged over 2-10 laser shots. LIF
3
a F
3
intensities were proportional to Ni number densities.
Reagents. The following reagents were used as received: Ni-
3
a F
2
3
a D
3
0.416
0.718
1.17
2.38
3.21
4.07
5.54
6.01
7.33
7.51
0.299
0.489
0.891
1.52
2.07
2.83
3.89
4.59
5.16
5.85
0.138
0.243
0.399
0.792
1.10
1.70
2.18
(C5H5)2 (Strem Chemicals, Inc., 99%), Ar (Potomac Airgas, Inc.,
0.107
0.176
0.336
0.476
0.737
1.06
99.998%), SO2 (MG Industries, 99.98%).
8
0
1
2
3
20
00
00
Data Analysis and Results
A typical decay trace is shown in Figure 1. It represents the
3
400
3.10
3.19
1.41
1.52
decay of Ni(a D3) in the presence of added SO2. Partial pressures
5
6
00
00
10
40
10
of the precursor nickelocene are not accurately known in these
experiments. However, based on the carrier flow rate and
pressure, total flow rate, and total pressure, nickelocene’s partial
pressure in the reaction chamber is estimated to be less than
4.01
1.95
a3D
2
a3D
1
0
.5 mTorr for all experiments. The solid line through the data
a
Buffer ) argon. Overall uncertainties are (30% at the 95%
is an exponential fit to the equation
confidence limit.
I ) I exp(-t/τ)
(1)
reproducibility of k, and instrumental uncertainties such as digital
o
delay and flow measurements. The rate constants for the
3
3
3
depletion of the a F4, a D3, and a D2 states are identical. These
rate constants increase with increasing total pressure and
decrease with increasing temperature, an indication of the
termolecular reaction mechanism
where I and Io are the LIF signals at time t and time t ) 0,
respectively, and τ is the lifetime from which the pseudo-first-
order rate constant, 1/τ, is obtained. 1/τ is given by
1
/τ ) 1/τ + k[SO ]
(2)
o
2
Ni + SO h Ni-SO *
(3)
(4)
2
2
Ni-SO * + M f Ni-SO + M
where τo is the lifetime of Ni without added SO2, k is the second-
order rate constant, and [SO2] is the partial pressure of SO2. τo
represents the lifetime of Ni in the presence of species other
than SO2 in the reaction chamber and diffusion out of the
detection zone. τo was usually long compared to τ. Second-
order rate constants were obtained from the slopes of plots of
2
2
The third body M was predominantly argon. The partial
pressures of the other gaseous components were too low to
contribute significantly to the stabilization of the NiSO * adduct.
2
Data were not collected above 600 Torr and 612 K because of
1
/τ vs SO2 partial pressure such as that shown in Figure 2. Note
a low signal-to-noise ratio under such conditions. Since the
depletion rate constants of the a F , a D , and a D states are
4 3 2
3
3
3
that the intercept (1/τo) is relatively small so that interference
from photofragments and diffusion was minimal.
identical, a thorough pressure and temperature-dependence study
3
The measured rate constants are listed in Table 2. The
uncertainties resulting from the linear regression fits, such as
that in Figure 2, were approximately 3% ((1σ) in precision.
The overall uncertainties, estimated at (30% at the 95%
confidence limit, include statistical scatter in the data, the
was undertaken for only Ni(a D3), because it had the largest
LIF signal.
3
Plots of the second-order rate constants (for a D3) as a
function of total pressure at all temperatures are shown in
Figures 3 and 4. The lack of any true bimolecular component

Depletion Kinetics of Ni Atoms by SO2
J. Phys. Chem. A, Vol. 103, No. 1, 1999 77
TABLE 3: Falloff Modeling Parameters for the Reaction of
6
4
Ni (a D1/2, a F
J
) with SO
2
(cm molecule s-1) k
6
-2
(cm molecule s-1
3
-1
)
F
c
T (K) k
o
∞
-
-
29
-10
2
3
3
4
6
96 (3.3 ( 0.3) × 10
(1.7 ( 0.4) × 10
0.64 ( 0.10
29
-10
49 (1.6 ( 0.2) × 10
1.5 × 10 (fix)
0.79 ( 0.07
-
-
-
29
29
29
-10
99 (0.84 ( 0.08) × 10
98 (0.51 ( 0.08) × 10
12 (0.26 ( 0.05) × 10
The simplified Lindemann-Hinshelwood mechanism, eq 7, was
used to fit the data. The uncertainties represent two standard deviations
precision).
(1.1 ( 0.2) × 10
(1.1 ( 0.5) × 10
a
a
a
-10
-10
(0.84 ( 0.47) × 10
a
(
3
Figure 3. Pressure dependence of Ni(a D
3
2
) + SO at (a) 296, (b) 399,
and (c) 612 K. The solid line through the data at 296 is a fit to eq 6,
and the solid lines through the other data are fits to eq 7. See Table 3
for results of fits.
o
Figure 5. Temperature dependence of k . The solid line through the
data is a polynomial fit. See text for results of fit. The error bars
represent the (2σ uncertainties (precision).
k∞ appears to decrease with increasing temperature. However,
the relatively long extrapolations of the second-order rate
constants to the high-pressure limit as the temperature increases
and the combined uncertainties in k∞ precluded an accurate
assessment of this observation. The k∞ values obtained from
eqs 6 and 7 are on the order of the gas kinetic rate constant of
3
Figure 4. Pressure dependence of Ni(a D
4
3
2
) + SO at (a) 349 and (b)
99 K. The solid lines through curves (a) and (b) are fits to eqs 6 (with
fixed k ) and 7, respectively. See Table 3 for results of fit.
∞
to the rate is consistent with the thermochemistry of the ground
state, bimolecular channel
-
10
3
-1 -1
∼2 × 10
cm molecule s , thus justifying the use of k∞
-
10
3
-1 -1
-1 6,7
) 1.5 × 10
cm molecule
s
for the 349 K data.
Ni + SO f NiO + SO
∆H ≈ 40 kcal mol
(5)
2
Table 2 shows that the excited states above 880 cm-1 deplete
at approximately the gas collision rate, an indication of no
activation barrier. The kinetics of these states were not
investigated at total pressures above 10 Torr due to decreasing
signal-to-noise ratios. A pressure dependence and a positive
temperature dependence are not expected since the depletion
rate constants are large.
being thermodynamically inaccessible at relatively low tem-
peratures. The solid line through the 296 data is a fit using Troe’s
formalism
9
ko[M]
+ (k [M]/k )
log Fc
log k ) log
+
(6)
2
1
o
∞
1 + [log (k [M]/k )]
o
∞
Discussion
where ko is the limiting low-pressure third-order rate constant,
k∞ is the limiting high-pressure second-order rate constant, [M]
is the buffer gas number density, and Fc is the broadening factor.
Large uncertainties (>100%) in the fitted parameters were
obtained when the higher temperature data were fitted to eq 6.
The results presented here indicate that the excited states
-
1
below 880 cm deplete at identical rates and/or the rate of
interconversion among them is fast. The thermal energy is 206
-
1
3
-1
cm and the a D state is only 205 cm above the ground
3
-
10
3
Thus, for the 349 K data, k∞ was fixed at 1.5 × 10
molecule in eq 6. The simplified Lindemann-Hinshel-
wood expression
cm
state. Thus, rapid interconversion is likely, at least between the
-
1
-1
3
3
3
3
s
4 3 3 2
a F and a D states. (Ni(a D ) and Ni(a D ) account for
13
approximately 22% and 3%, respectively, of the thermal
3
3
3
population at 296 K.) Ni(a F4), Ni(a D3), and Ni(a D2) were
also found to react with NO at identical rates at ∼1 Torr total
pressure, and none of these states reacted with O2 and N2O.14
Rapid interconversion between the states was not indicated in
k ) k [M]/(1 + k [M]/k )
(7)
o
o
∞
was used for the higher temperature data. Results of the fits are
given in Table 3. ko decreases with increasing temperature, as
shown in Figure 5, and can be expressed as
that work. It thus appears that the depletion mechanism of Ni-
3
(
a D2) in the presence of small oxidants is similar to that of
3
3
8
2
Ni(a F4) and Ni(a D3). The 3d 4s electron configuration of the
ground state does not appear to introduce any barriers to
ko(T) ) 7.455-24.41(log T) +
.993(log T) cm molecule s-1 (8)
2
6
-2
reaction. Since the a F4 state is in thermal equilibrium with the
3
3

78
J. Phys. Chem. A, Vol. 103, No. 1, 1999
McClean
9
1 3
3
d 4s a D3 state, any barriers due to the closed s-subshell could
oxygen atoms, are observed and calculated. The binding energy
of NiSO2 estimated in this work is approximately equal to the
be screened. On the basis of the orbital-occupancy argument
presented above, we conclude that the ground state is converted
to the a D3 state, which is reactive. k∞ is close to the gas kinetic
2
binding energy of C2V η O,O Ni-O2 from an ab initio study: Eb
3
-1 22
) 48 ( 7 kcal mol . This observation suggests that the
rate constant, and ko decreases with increasing temperature,
indications of no energy barrier to product formation.
bonding in C2V NiO2 and C2V NiSO2 is similar. Covalent and
ionic components are present in NiO2. The relatively large
limiting low-pressure and high-pressure rate constants for Ni
Physical quenching is the likely depletion channel of the states
6
-
1
+ SO2 and the larger electron affinity of SO2 (than O2) suggest
above 880 cm . An abstraction channel is not accessible, and
-
10
3
-1
an ionic component in NiSO2.
rate constants on the order of 10
cm s for a termolecular
The reaction of Mn(3d 4s a6S5/2) with SO2 was also
5
2
channel at only 10 Torr total pressure is not expected. E-V
energy transfer may take place via the vibrational modes of SO2
investigated in this work to determine if a relatively unreactive
-
14
3
TM atom would react with SO2. An upper limit of ∼10 cm
since the energy differences between the Ni states are close to
-
1
-1
the vibrational modes of SO2.7
molecule
s
was obtained over the temperature range of
2
96-622 K. The electron-transfer mechanism has been offered
To estimate the binding energy Eb of the NiSO2 adduct
as an explanation for the reactions of TM atoms with SO2. The
ionization energy of Mn is less than that of Ni. Thus, the orbital
3
relative to Ni(a D3), simplified RRKM calculations using the
6
9
formalism of Troe were performed at 296 K. In brief, the rate
occupancy of the TM atom is the predominant driving force
constant for the unimolecular dissociation in the low-pressure
limit, kuni, of NiSO2 was first calculated. ko was then calculated
from the equilibrium expression Keq ) kuni/ko, where Keq is the
equilibrium constant for NiSO2 h Ni + SO2. The collision
efficiency, âc, of Ar was assumed to be 0.20. âc can be
determined by comparing the experimental and calculated
(at least when comparing Mn and Ni).
Summary and Conclusions
Results presented here indicate that Ni is very reactive toward
3
3
3
SO2. The three lowest states of Ni, a F4, a D3, and a D2, react
with SO2 via a termolecular mechanism. The 1:1 adduct
formation is efficient. The kinetic results were combined with
DFT and RRKM calculations to provide an estimate of 47 kcal
(strong collision) third-order rate constants. However, the
uncertainties and adjustable binding energy in the calculations
precluded such an approach. The molecular structure and
vibrational frequencies of NiSO2 needed for the RRKM calcula-
-
1
2
mol for the binding energy of NiSO2 (η O,O isomer). A
comparison between NiO and NiSO suggest covalent and ionic
8
tions were calculated from density functional methods. The
2
2
3
3
3
components to the bonding in NiSO2. The a F3, a F2, and a D1
states of Ni deplete at approximately the gas collision rate in
the presence of SO2.
binding energy was varied until agreement was obtained
between the calculated and experimental third-order rate con-
stant. The density functional calculations are not intended to
be exhaustive, but instead serve mainly to provide estimates of
the molecular parameters.
Acknowledgment. This research was supported by the Naval
Academy Research Council and a Cottrell College Science
Award of Research Corporation.
The molecular parameters of NiSO2 were calculated by the
15,16
SPARTAN
suite of programs. Calculations were performed
with the LSDA/pBP86 model and DN** numerical basis sets.
Several triplet isomers were assumed. The “side-on bonded,”
η O,O isomer (C2V geometry) gave the lowest energy. The DFT
results are to be taken with caution; numerical errors are likely
since calculations involve numerical integration steps. Addition-
ally, the relatively large number of low-lying states of Ni and
other TM atoms poses a challenge for the theoretical treatment
of transition metals. Pertinent output from the computations are
listed in the Appendix.
Appendix
2
The DFT suite of SPARTAN programs15,16 was used to
calculate the molecular parameters of NiSO2. For the triplet η O,O
2
isomer of NiSO2 (C2V geometry), we found bond lengths of r(S-
O) ) 1.5847 Å and r(O-Ni) ) 1.9539 Å. Bond angles are
∠ (O-S-O) ) 100.1412°, ∠ (S-O-Ni) ) 91.4730°, and ∠ (O-
Ni-O) ) 76.9128°. Calculated frequencies, in units of cm ,
are 127.12, 301.61, 349.38, 504.62, 836.33, and 841.61.
For the simplified RRKM calculations at 296 K, Eo was taken
as an adjustable parameter. The rate constant for the unimo-
lecular dissociation in the low-pressure limit, kuni, is given by 9
-
1
Agreement between the measured and calculated ko at 296
-
1
K was obtained for Eb ) 47 ( 3 kcal mol ; the uncertainty in
Eb is based only on the overall uncertainty in ko at 296 K. Since
there is no activation barrier, significantly smaller Eb values
would give association rate constants that are too small because
ko is a sensitive function of the binding energy.13 The presence
of several low-lying states in atomic Ni and the possibility of
several low-lying bound states in NiSO2 could lead to additional
pathways, thus affecting the calculated results. The equilibrium
constant, and hence ko, is also affected by the relatively low
level of the DFT calculations. Thus, only an estimate of Eb is
reported. This estimate is reasonable, however. A comparison
of the rates of TM and main-group metals with small oxygen-
containing molecules indicates that a bond energy of 40-50
F(E )RT
Qvib
o
kuni ) âCZLJ
exp(-E /RT)F F F FrotintnFcorr
o anh E rot
where âC is the collisional efficiency of Ar, ZLJ is the Leonard-
Jones rate constant, F(Eo) is the vibrational density of states of
NiSO2 at the threshold energy Eo for dissociation, Qvib is the
vibrational partition function of NiSO2, Fanh is a correction for
vibrational anharmonicity, FE is a correction for the variation
of the density of states, and Frot is the molecular rotational
correction factor. The corrections for internal rotational modes
and the coupling of the F factors, Frot int and Fcorr, were taken
as one.
-
1
kcal mol is in accord with third-order rate constants of the
magnitude measured in this work.1
7-21
-
10
cm3
The binding energies of Na-SO2 and K-SO2 have been
A Lennard-Jones collision frequency of 6.38 × 10
-
1
-1
found to lie within the range of the corresponding binding
molecule was calculated from reasonable values of the
s
energies of the metal-O2 superoxides.1
9,20
C2V η O,O-type
2
Lennard-Jones parameters. âc was taken as 0.20. s ) 6 and m
) 3, where s is the number of vibrational modes in NiSO2 and
structures, where the alkali-metal atoms are side-bonded to the

Depletion Kinetics of Ni Atoms by SO2
J. Phys. Chem. A, Vol. 103, No. 1, 1999 79
m is the number of vibrational modes that has disappeared after
(11) Moore, C. E. Atomic Energy Levels as Derived from the Analysis
of Optical Spectra. Natl. Stand. Ref. Data Ser. (U.S. Natl. Bur. Stand.) 1971,
NSRDS-NBS 35.
-1
dissociation. Eo ) 47 kcal mol . Calculated RRKM parameters
are a(Eo) ) 0.989, Fanh ) 1.37, FE ) 1.06, and Frot ) 22.4,
where a(Eo) is a constant calculated from the energy. Calculated
(12) Martin, G. A.; Fuhr, J. R.; Wiese, W. L. J. Phys. Chem. Ref. Data
1988, 17, Suppl. 4.
(13) Gilbert, R. G.; Smith, S. C. Theory of Unimolecular and Recom-
bination Reactions; Blackwell Scientific Publications: Boston, 1990.
-
10
-3
Keq, kuni, and ko values are 3.14 × 10
molecule cm , 5.17
-38
3
-1 -1
-29
6
-2
×
10 cm molecule s , and 3.30 × 10 cm molecule
1
(
79.
14) Matsui, R.; Senba, K.; Honma, K. J. Phys. Chem. A 1997, 101,
-
s , respectively.
1
(
15) SPARTAN; Wavefunction, Inc.: Irvine, CA, 1997.
References and Notes
(16) Hedre, W. J.; Lou, L. A Guide to Density Functional Calculations
in SPARTAN; Wavefunction, Inc.: Irvine, CA, 1997.
17) Brown, C. E.; Mitchell, S. A.; Hackett, P. A. J. Phys. Chem. 1991,
5, 1062 and references therein.
18) Parnis, J. M.; Mitchell, S. A.; Hackett, P. A. J. Phys. Chem. 1990,
4, 8152 and references therein.
19) Goumri, A.; Laakso, D.; Rocha, J.-D. R.; Francis, E.; Marshall, P.
J. Phys. Chem. 1993, 97, 5297.
(
1) McClean, R. E.; Campbell, M. L.; Kolsch, E. J. J. Phys. Chem. A
997, 101, 3348.
2) Campbell, M. L.; Hooper, K. L.; Kolsch, E. J. Chem Phys. Lett.
997, 274, 7.
(
1
1
1
9
9
(
(
(3) McClean, R. E.; Campbell, M. L.; Goodwin, R. H. J. Phys. Chem.
(
996, 100, 7502.
(4) Harter, J. S. S.; Campbell, M. L.; McClean, R. E. Int. J. Chem.
(20) Shi, Y.; Marshall, P. J. Phys. Chem. 1991, 95, 1654.
Kinet. 1997, 29, 367.
(
21) Nien, C.-F.; Rajasekhar, B.; Plane, J. M. C. J. Phys. Chem. 1993,
(
(
5) Campbell, M. L.; McClean, R. E. J. Phys. Chem. 1993, 97, 7942.
6) CRC Handbook of Chemistry and Physics, 75th ed.; Lide, D. R.,
9
7, 6449.
-
1
Ed.; CRC Press: Boca Raton, FL, 1995.
7) JANAF Thermochemical Tables, 3rd ed. J. Phys. Chem. Ref. Data
(22) The binding energy of 48 ( 7 kcal mol was obtained from
(
Bauschlicher, C. W., Jr.; Langhoff, S. R.; Partridge, H.; Sodupe, M. J. Phys.
Chem. 1993, 97, 856. A kinetic study of Ni + O2 yielded a binding energy
Chase, M. W., Jr., Davies, C. A., Downey, J. R., Jr., Frurip, D. J., McDonald,
R. A., Syverud, A. N., Eds.; 1985, 14, Suppl. 1.
-
1
of 57 kcal mol (ref 23), and a previous theoretical study yielded a value
-
1
(
8) Modern Density Functional Theory: A Tool for Chemistry;
Seminario, J. M., Politzer, P., Eds.; Elsevier: New York, 1995.
9) Troe, J. J. Phys. Chem. 1979, 83, 114.
10) Campbell, M. L.; McClean, R. E. J. Chem. Soc., Faraday Trans.
995, 91, 3787.
of 18 kcal mol (ref 24).
(23) Mitchell, S. A. In Gas-Phase Metal Reactions; Fontijn, A., Ed.;
Elsevier: Amsterdam, 1992; p 227.
(24) Blomberg, M. R. A.; Siegbahn, P. E. M.; Strich, A. Chem. Phys.
1985, 97, 287.
(
(
1