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are used to describe the CO2 formation. In fact, the TV and
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850 K) on Pd(110) (Figure 13a and 14a). In the CO + O2
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dissociation, which reacts with CO immediately after the
formation, may not be accommodated to the surface, and such
a hot O atom can affect the extent of the vibrational excitation.
Such dynamic roles of nascent hot oxygen have also been
observed in other reaction systems.43-46 In this case, the rate
constant kr in the CO + NO reaction (eq 7) may be larger than
that in the CO + O2 reaction (eq 23), which results in lower θO
values in Figure 2c and f. Further investigation is necessary for
the elucidation of the mechanism for the excitation of the
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B
the bending vibrational one (TVB) on Pd(110). In contrast, TV
was higher than TVAS on Pd(111). These behaviors suggest that
the activated complex for CO2 formation is more bent on Pd-
(111) than that on Pd(110), which is reflected by the surface
B
AS
smoothness. Both TV and TV increased gradually with
increasing surface temperature (TS).
(4) From the IR emission spectra of CO2 during the CO +
AS
B
NO reaction over both Pd surfaces, TV decreased and TV
increased significantly with increasing TS. TVB was higher than
AS
B
TV at higher temperatures (above 700 K). TV in CO + NO
reactions on Pd(110) at 800 and 850 K was much higher than
that in CO + O2 reactions, which was discussed in terms of the
large difference in the oxygen coverage and the difference in
the dynamics of both reactions.
Acknowledgment. This work has been supported by the 21st
Century Center of Excellence (COE) Program under the
Ministry of Education, Culture, Sports, Science, and Technology
(MEXT), Japan.
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References and Notes
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