Photodissociation dynamics of ketene at 157.6 nm

Article abstract of DOI:10.1063/1.2147221

Photodissociation dynamics of ketene at 157.6 nm has been investigated using the photofragment translational spectroscopic technique based on photoionization detection using vacuum-ultraviolet synchrotron radiation. Three dissociation channels have been observed: C H2 +CO, CH+HCO, and HCCO+H. The product translational energy distributions and angular anisotropy parameters were measured for all three observed dissociation channels, and the relative branching ratios for different channels were also estimated. The experimental results show that the direct C-C bond cleavage (C H2 +CO) is the dominant channel, while H migration and elimination channels are very minor. The results in this work show that direct dissociation on excited electronic state is much more significant than the indirect dissociation via the ground state in the ketene photodissociation at 157.6 nm.

Full text of DOI:10.1063/1.2147221

Photodissociation dynamics of ketene at 157.6 nm
I-Chung Lu, Shih-Huang Lee, Yuan T. Lee, and Xueming Yang
Citation: The Journal of Chemical Physics 124, 024324 (2006); doi: 10.1063/1.2147221
View online: http://dx.doi.org/10.1063/1.2147221
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/124/2?ver=pdfcov
Published by the AIP Publishing
Articles you may be interested in
Photodissociation dynamics of C3H5I in the near-ultraviolet region
J. Chem. Phys. 141, 104316 (2014); 10.1063/1.4894393
Photodissociation dynamics of 3-bromo-1,1,1-trifluoro-2-propanol and 2-(bromomethyl) hexafluoro-2-propanol at
234 nm: Resonance-enhanced multiphoton ionization detection of Br (2 P j )
J. Chem. Phys. 134, 194313 (2011); 10.1063/1.3591373
Photodissociation dynamics of vinyl fluoride ( C H 2 C H F ) at 157 and 193 nm : Distributions of kinetic energy
and branching ratios
J. Chem. Phys. 125, 144315 (2006); 10.1063/1.2357946
Distributions of angular anisotropy and kinetic energy of products from the photodissociation of methanol at 157
nm
J. Chem. Phys. 121, 11053 (2004); 10.1063/1.1814099
C–Cl bond fission dynamics and angular momentum recoupling in the 235 nm photodissociation of allyl chloride
J. Chem. Phys. 121, 11016 (2004); 10.1063/1.1812757
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
209.183.185.254 On: Sun, 23 Nov 2014 05:04:06

THE JOURNAL OF CHEMICAL PHYSICS 124, 024324 ͑2006͒
Photodissociation dynamics of ketene at 157.6 nm
I-Chung Lu
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
Shih-Huang Lee
National Synchrotron Radiation Research Center, Husinchu 30076, Taiwan
Yuan T. Lee
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan
a͒
Xueming Yang
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116011, China
͑
Received 29 August 2005; accepted 9 November 2005; published online 13 January 2006͒
Photodissociation dynamics of ketene at 157.6 nm has been investigated using the photofragment
translational spectroscopic technique based on photoionization detection using vacuum-ultraviolet
synchrotron radiation. Three dissociation channels have been observed: CH +CO, CH+HCO, and
2
HCCO+H. The product translational energy distributions and angular anisotropy parameters were
measured for all three observed dissociation channels, and the relative branching ratios for different
channels were also estimated. The experimental results show that the direct C–C bond cleavage
͑
CH +CO͒ is the dominant channel, while H migration and elimination channels are very minor.
2
The results in this work show that direct dissociation on excited electronic state is much more
significant than the indirect dissociation via the ground state in the ketene photodissociation at
157.6 nm. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2147221͔
3 1A potential-energy surface is C -I symmetry ͑out-of-
I. INTRODUCTION
1
S
plane bent͒. Up until now, most photodissociation studies of
Ketene ͑CH CO͒ has received much attention in the
ketene were focused on the diffuse absorption band region,
2
1
1
field of photochemistry. It has been long known as the pho-
tochemical source of methylene radical in both interstellar
space and in laboratory work. Moreover, ketene has proven
to be a benchmark system for theoretical study of unimolecu-
to the 1 A and 1 B states.
2 1
In this work, ketene photodissociation at 157.6 nm exci-
1
tation to the 3 A electronic state was investigated. Several
1
product channels are energetically accessible at 157.6 nm ex-
citation ͑see Fig. 1͒. A molecular-beam apparatus based on
synchrotron radiation as the ionization detection scheme was
used this work. Time-of-flight spectra were obtained by the
photofragment translational spectroscopy ͑PTS͒ technique.
The product angular anisotropic parameter ␤ for these chan-
nels was measured, and the relative branching ratio of differ-
ent channels have also been estimated.
1
,2
lar dissociation. Photodissociation of ketene in a collision-
3
free environment has been investigated at 193 nm excitation
and longer wavelengths.
CvC bond cleavage channels have been observed as major
primary photodissociation pathways. Previous experimental
results suggest that the H atom elimination channel at
4
–8
Both H atom elimination and
193 nm excitation occurs on the ground electronic state sur-
face and exhibits clear statistical signature, CvC bond fis-
sion process was the main focus of previous ketene photo-
II. EXPERIMENT
dissociation studies. Both triplet and singlet CH radicals
2
have been observed in this dissociation process. Previous
The experimental apparatus and method are described in
1
11
12–15
studies indicate that CH ͑ A ͒ was produced by internal con-
detail in a previous publication and elsewhere.
In order
2
1
version from S state to ground state ͑S ͒, while the ground-
to understand the dissociation dynamics of ketene at
157.6 nm clearly, photofragment time-of-flight ͑TOF͒ spec-
tra were measured in a molecular-beam apparatus with
vacuum ultraviolet ͑vuv͒ ionization. The character of this
apparatus is the tunable vuv photon beam to ionize the neu-
tral photofragment in the ionization region of the detector.
The tunable vuv photon beam comes from the U9 beamline
of the National Synchrotron Radiation Research Center in
Hsinchu, Taiwan. The molecular-beam machine consists of
three parts: the rotatable source, the reaction chamber, and
the fixed detector. A pulsed molecular beam of 10% ketene
seeded in Ar was made by expanding the sample from source
chamber into the reaction main chamber with a backing pres-
1
0
3
state CH ͑ B ͒ radical is produced from intersystem crossing
2
1
to the T potential-energy surface after vertical excitation.
1
The vacuum-uv absorption spectrum of the ketene mol-
ecule has been measured previously. The electron transition
1
1
around 157.6 nm was assigned to the 3 A ͑3d͒-X A
1
1
9
,10
1
band.
There are three lower 3d Rydberg states, 3 A ,
1
1
1
1
3
B , and 3 A . The transition to the lowest ͑3 A ͒ 3d Ry-
dberg state has the largest oscillator strength. The theoretical
calculations also show that the symmetry of the ketene in
1
2
1
1
0
a͒Author to whom correspondence should be addressed. Electronic mail:
xmyang@dicp.ac.cn
0
021-9606/2006/124͑2͒/024324/6/$23.00
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
09.183.185.254 On: Sun, 23 Nov 2014 05:04:06
124, 024324-1
© 2006 American Institute of Physics
2

024324-2
Lu et al.
J. Chem. Phys. 124, 024324 ͑2006͒
FIG. 1. Schematic energy diagram for the photodisso-
ciation channels of ketene at 157.6 nm ͑181.4
kcal/mol͒ excitation.
sure of 700 Torr. The molecular beam was intersected at 90°
using vacuum distillation from 195 to 77 K several times to
remove impurities such as CO and CH COOH.
with a F excimer laser ͑157.6 nm͒ beam, Lambda Physik
2
2
3
LPF 220i F. In order to avoid the multiphoton dissociation
effect, the 157.6 nm laser power was attenuated by one or
two mesh screens to be about 0.5–1 mJ per pulse during the
experiment. The vacuum pressure of the reaction chamber
was maintained at 2ϫ10 Torr evacuated by a 2000 l/s tur-
bomolecular pump and a cryopump, thus a collision-free
condition was achieved. After flying about 100 mm from the
crossed region, the neutral reaction products were ionized by
the tunable synchrotron vuv photon beam. For the sake of
sufficiently ionizing the reaction products, we employed a
windowless noble gas filter in the beamline to substitute for
The product TOF spectra from photodissociation of the
ketene compounds were measured in the laboratory frame. In
order to obtain the center-of-mass translational energy distri-
butions P͑ET͒, the analysis of the laboratory TOF spectra
was performed using a forward convolution program, PHOT-
RAN. In this computer program, the spectra of two momen-
tum matched fragments produced in a binary dissociation
process can be simulated using a translational energy distri-
−
8
bution P͑ET͒.
III. RESULTS AND DISCUSSIONS
a monochromoator. The photon flux of tunable vuv beam is
estimated to be about 1016 photon s−1 and the spectrum en-
In this experiment, TOF spectra of the products pro-
duced in the photodissociation of ketene at 157 nm were
measured using vuv photoionization technique. Signals of
the photodissociation products from ketene photolysis at
ergy resolution is about 3%. In this experiment, the synchro-
tron photon energy is tunable by adjusting the gap of the
undulator device raging from 30 to 36 nm, corresponding to
+
+
+
+
mass 13͑CH ͒, 14͑CH ͒, 28͑CO ͒, 29͑HCO ͒, and
2
1
1–17.5 eV. The ionization region was evacuated to less
+
4
1͑HCCO ͒ have been detected. After careful measurement
and detailed analyses of the TOF spectra, three dissociation
−
12
than 4ϫ10 Torr with several turbomolecular pumps and a
liquid-nitrogen-cooled trap. After ionization, the photofrag-
ment ions are focused by ion optics, mass selected by a
quadrupole mass filter, and recorded with a Daly-type ion
counter. The TOF spectra for different fragment from the
photodissociation of ketene at 157.6 nm have been measured
using the apparatus described above. To obtain a TOF spec-
trum with a good signal-to-noise ratio, the experimental TOF
channels were identified: the CH +CO channel, the CH
2
+
HCO channel, and the HCCO+H channel. Anisotropy pa-
rameters have also been determined for all observed photo-
fragments.
A. CH +CO channel
2
5
+
spectra were taken by averaging over about ϳ5ϫ10 laser
Figure 2 shows the TOF spectra of mass 14͑CH ͒ and
2
+
shots. The measurement of angular anisotropy of products
has been carried out in the photolysis of ketene at 157 nm. In
this experiment, the TOF spectra for different products at
different laser polarizations are measured using a thin-film
polarizer ͑Laseroptik GmbH͒. The polarizer setup is de-
mass 28͑CO ͒ from the photodissociation of ketene at
57.6 nm. In the TOF spectra of mass 14, no significant dis-
1
sociative ionization was observed by tuning the detection
photon energy from the ionization threshold to 14 eV. The
TOF spectra at mass 14 and mass 28 at 30° can be easily
simulated using a single kinetic-energy distribution, indicat-
ing that products are momentum matched and from a single
1
,16
scribed in detail elsewhere.
Ketene ͑CH CO͒ was synthesized according to literature
2
procedures through thermal decomposition of acetic anhy-
dride ͑Aldrich 99%͒ at temperature ϳ800 K. The ketene
thus formed was collected using a liquid nitrogen bath at
binary channel. The translational energy distribution P͑E ͒ is
T
1
7
shown in Fig. 3͑a͒. These two TOF spectra can be assigned
to the CH +CO channel.
2
77 K; most of the by-product such as acetic acid was trapped
Figure 4 shows the TOF spectra of CH and CO detected
2
at 185 K using a dry ice/methanol slush before entering the
sample collector. The reaction products were then purified
using dissociating light with polarization parallel and perpen-
dicular to the TOF axis. The angular anisotropy parameter ␤
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
09.183.185.254 On: Sun, 23 Nov 2014 05:04:06
2

024324-3
Photodissociation dynamics of ketene
J. Chem. Phys. 124, 024324 ͑2006͒
FIG. 2. ͑a͒ The TOF spectra of mass 28 product at the laboratory angle of
0° using 14.5 eV photon energy. Curve 1 is the contribution from CH2
CO channel. Curve 2 was simulated by dissociation ionization from the
HCO radical. ͑b͒ TOF spectra of mass 14 at the laboratory angle of 30°
using 12.8 eV photon energy. The opened circles are the experimental data
points, while the solid lines are the simulated contributions.
FIG. 3. ͑a͒ The translational energy distribution P͑E ͒ of CH +CO channel.
T
2
3
+
͑
b͒ P͑E ͒ of CH+HCO channel. The error bars for the two distributions are
T
about ±10%.
the anisotropy parameter is positive, suggest that transition
dipole moment should be parallel to the C–C–O plane. It is
also clear that the lifetime of this dissociating molecule is not
sufficiently long to smear the angular anisotropy parameter
totally. Quite likely, the dissociation time should be compa-
rable to the rotational time of the parent molecule.
is about 0.7 near the peak. It is clear that the angular aniso-
tropy parameter is translational energy dependent. The
slower part of the signal is from the HCO channel, the an-
isotropy of this channel is clearly zero. The seemed energy
dependence of ␤ could be partly from the overlapped signals
between the CH +CO channel and the HCO+CH channel.
B. CH+HCO channel
2
In addition, the direct dissociation of CH +CO could also
+
+
2
The TOF spectra at mass 13͑CH ͒ and mass 29͑HCO ͒
have also been observed at a laboratory angle of 30°, as
shown in Fig. 5. As we can see in Fig. 5͑a͒, the fast curve 1
exhibit an energy-dependent angular anisotropy as in many
1
8
other cases. If direct bond dissociation coupled with an
angular motion, it is possible that product angular anisotropy
is strongly energy dependent. Photodissociation of ketene in
this channel with 193 nm has been previously studied by
13
is attributed to the contribution from the C of CO molecule
m/e=29͒. Another slower curve 2 can be assigned to the
͑
CH+HCO channel signal. This component can be momen-
tum matched with the slower part ͑curve 2͒ of the TOF spec-
trum at mass 13 ͓Fig. 5͑b͔͒ using the same kinetic-energy
distribution shown in Fig. 3͑b͒. There are three distinct fea-
tures in the TOF spectra of mass 13 shown in Fig. 5͑b͒. The
small and fast peak ͑curve 1͒ is attributed to the dissociative
1
9
20
Fujimoto et al. and Sonobe and Rosenfeld. Their study
indicated clearly that CO product is highly vibrationally and
rotationally excited, since dissociation process via a nonlin-
ear geometry. In this case, the energetic limit of the product
translational energy distribution is consistent with the limit
1
1
+
of the CH ͑ B ͒+CO͑ ⌺ ͒ channel. The dissociation process
2
1
ionization of CH product. This peak could be fitted using
2
is spin allowed since the initially excited state is also a sin-
the kinetic-energy distribution shown in Fig. 3͑a͒. In addi-
tion, the slowest part ͑curve 3͒ is clearly from the cracking of
mass 41 product ͑HCCO͒ from the H atom elimination that
will be discussed later.
Since the energy of this channel is quite high,
ϳ173.4 kcal/mol, this channel only opens up at very high
excitation energy. The available energy for this dissociation
glet state. The average product translational energy, ͗E ͘, is
T
about 36% of the total available energy for this channel. This
is consistent with the theoretical calculations that the initial
1
excitation is to the 3 A state, a diffusive Rydberg state that
1
is likely coupled to a direct dissociative state. A positive ␤
parameter for this channel also supports this picture. Since
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
09.183.185.254 On: Sun, 23 Nov 2014 05:04:06
2

024324-4
Lu et al.
J. Chem. Phys. 124, 024324 ͑2006͒
FIG. 5. ͑a͒ TOF spectra of mass 29 product at the laboratory angle of 30°
FIG. 4. Upper panel: TOF spectra of mass 28 ͑CO͒ product at ␪=30° mea-
sured at two different photolysis polarization direction using 15.5 eV ion-
ization photons. Lower panel: the anisotropy parameter obtained for the
1
3
using 11 eV photon energy. Curve 1 is the contribution from the CO
simulated by CH +CO channel. Curve 2 was simulated by HCO+CH chan-
2
nel. ͑b͒ TOF spectra of mass 13 at the laboratory angle of 30° using 12.8 eV
photon energy. The solid lines are the simulated contributions from three
channels: ͑1͒ cracking of the CH radical from CH +CO channel, ͑2͒ CH
CH +CO channel.
2
2
2
channel at 157.6 nm is only ϳ8 kcal/mol, which is consis-
product from CH+HCO channel, and ͑3͒ cracking of HCCO radical from H
elimination channel.
tent with the experimentally observed P͑E ͒. The averaged
T
translational energy release ͗E ͘ is only 0.9 kcal/mol, indi-
T
cating only 11% of the total available energy is deposited to
the product translational energy. This suggests that most of
the available energy is deposited into the internal energy of
the two radicals ͑CH and HCO͒. The product angular aniso-
tropy parameter of this channel was determined to be zero,
this dissociation channel dissociated through an intermediate
that lives much longer than the rotational period of the parent
molecule. Clearly, this channel requires a H atom migration
before bond dissociation. It is quite possible that the disso-
ciation of this channel occurs via internal conversion to the
ground before dissociation occurs, suggesting that dissocia-
tion of this channel might be rather statistical. The transla-
5
6
6 kcal/mol, which is a little below the available energy,
6 kcal/mol. About 30% of the total available energy is de-
posited in the translational degrees of freedom, indicating
that majority of the available energy is deposited into the
internal energy degrees of freedom of the HCCO radical.
21
In the ketene photodissociation at 193 nm, the experi-
mental results suggest that the H atom elimination C–H bond
occurs on the S PES. The maximum of the total kinetic-
0
energy release ͑TKER͒ of the H elimination channel at
1
93 nm is about 44.3 kcal/mol, and it peaks at
ϳ3.8 kcal/mol. For the ketene photodissociation at
57.6 nm, the internal excitation of the hot HCCO radical is
1
tional energy distribution P͑E ͒ for this channel shows a
T
clearly higher than that at 193 nm. Anisotropy parameter ␤
was also found to be zero for this channel at 157 nm. It is
interesting to point that the peak position of the translational
energy distribution for this channel at 157.6 nm,
ϳ13 kcal/mol, is much higher than that at 193 nm. This in-
dicates that the dynamics of ketene photodissociation at
157 nm is slightly different from that at 193 nm. If ketene
photodissociation at the two wavelengths are similar and oc-
curs on the ground-state surface via internal conversion with
energy fully randomized, the peak position of the product
translational energy should be more or less the same for the
two wavelengths. However, this is not the case here, which
peak at 0.9 kcal/mol, implying that this process has a small
dissociation barrier of 0.9 kcal/mol.
C. HCCO+H channel
The H atom elimination channel has also been observed.
The TOF signals at different angles have been detected at
+
mass 41͑HCCO ͒. Two of the spectra are shown in Fig. 6.
These TOF spectra can be simulated using the translational
energy distribution shown in Fig. 7. The translational energy
distribution for the H elimination process peaks at
ϳ13 kcal/mol and the sharp cutoff at kinetic energy of
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
09.183.185.254 On: Sun, 23 Nov 2014 05:04:06
2

024324-5
Photodissociation dynamics of ketene
J. Chem. Phys. 124, 024324 ͑2006͒
TABLE I. Branching ratios for all product channels in photolysis of ketene
at 157.6 nm.
Dissociation channel
Branching ratio ͑%͒
CH +CO
97
0.9
2.1
2
CH+HCO
HCCO+H
D. Branching ratios
The relative branching ratios of different ketene photo-
dissociation channels at 157.6 nm have been determined. To
determine the branching ratios, we have measured all of the
TOF signals that could be detected at the ionization photon
energy at 17 eV in order to mimic the condition of the elec-
tron impact ionization, where the photoionization cross sec-
tion do not drastically. In the estimation of the branching
ratios, we assume that the detection efficiency is the same for
all the detected fragments. This assumption of estimating
2
2
branching ratios has been proved to quite reasonable. The
estimated branching ratios are listed in Table I.
The dominant channel of ketene photodissociation at
1
57.6 nm is the CH +CO channel. Clearly the dynamics of
2
this dissociation is significantly different from the other two
channels. This dissociation process occurs likely via a strong
coupling between the excited Rydberg state and a repulsive
state, while the other two photodissociation channels, CH
FIG. 6. The TOF spectra of mass 41͑HCCO͒ product at the laboratory
angles of 20° and 30° using 12.8 eV photon energy. The open circles are the
experimental data points, while the solid lines are the simulated
contributions.
+
HCO and HCCO+H, proceed likely via internal conver-
sion to the ground state from the excited Rydberg state. The
observed branching ratios reflect largely the relative
strengths of the two type couplings. Obviously, the excited
state couples to the repulsive much more strongly than that
to the ground state.
suggests that the H atom elimination may not be fully statis-
tically albeit it is possible that this channel occurs on the
ground state. This is likely due to the dynamical imprint
from the internal conversion that affects the H atom elimina-
tion dynamics. No H atom signal has been detected for this
channel using the same setup. This is probably due to the low
signal levels of these channels, which is likely beyond the
sensitivity of our apparatus.
IV. CONCLUSIONS
Photodissociation dynamics of ketene at 157.6 nm has
been investigated using photofragment translational spectros-
copy ͑PTS͒. Three distinct dissociation pathways have been
observed. The dominant dissociation channel is CH +CO
2
with 97% yield, while the CH+HCO and H+HCCO chan-
nels are also present but with only ϳ0.9% and ϳ2.1% yield.
Product translational energy distributions for these two dis-
sociation channels have been determined from simulating the
experimental time-of-flight spectra. In addition, the averaged
product angular anisotropy parameter for the CH +CO
2
channel is determined to be 0.6, indicating that this dissocia-
tion channel should be a rather fast dissociation process via
excited states. This dissociation channel is likely via an in-
tersystem crossing process from the Rydberg excited surface,
1
3
A1͑3d͒, to a direct dissociation state with very strong cou-
pling. The experimental results indicate that both CH
HCO and H+HCCO channels have an anisotropy param-
+
eter of zero, implying that these two channels likely occur on
the ground surface through internal conversion from the ex-
cited surface, even though the dissociation is not necessary
fully statistical.
FIG. 7. The translational energy distribution used to simulate the TOF spec-
tra of the dissociation products from the H atom elimination channel. The
error bars for the two distribution are about ±10%.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
09.183.185.254 On: Sun, 23 Nov 2014 05:04:06
2

024324-6
Lu et al.
J. Chem. Phys. 124, 024324 ͑2006͒
9
0
ACKNOWLEDGMENTS
S. Y. Chiang, M. Bahou, Y. J. Wu, and Y. P. Lee, J. Chem. Phys. 117,
4
306 ͑2002͒.
1
This work was supported by the National Research
Council and the Academia Sinica of Taiwan. We also thank
for the support from National Synchrotron Radiation Re-
search Center in U9 chemical dynamics beam line and fi-
nance. One of the authors ͑X.Y.͒ would like to thank the
support from the Ministry of Science and Technology of
China, the Chinese Academy of Sciences, and the National
Natural Science Foundation of China.
P. G. Szalay, A. G. Csaszar, and L. Nemes, J. Chem. Phys. 105, 1034
͑1996͒.
I.-C. Lu, J. J. Lin, S.-H. Lee, Y. T. Lee, and X. Yang, Chem. Phys. Lett.
11
3
82, 665 ͑2003͒.
12
C. C. Wang, Y. T. Lee, J. J. Lin, J. Shu, Y. Y. Lee, and X. Yang, J. Chem.
Phys. 117, 153 ͑2002͒.
J. J. Lin, Y. Chen, Y. Y. Lee, Y. T. Lee, and X. Yang, Chem. Phys. Lett.
361, 374 ͑2002͒.
S.-H. Lee, Y. Y. Lee, Y. T. Lee, and X. Yang, J. Chem. Phys. 119, 827
1
1
1
3
4
5
͑
2003͒.
X. Mu, I.-C. Lu, S.-H. Lee, X. Wang, and X. Yang, J. Chem. Phys. 121,
684 ͑2004͒.
1
M. L. Costen, H. Katayanagi, and F. E. Hall, J. Phys. Chem. A 104,
4
1
0247 ͑2000͒.
16
2
3
S.-H. Lee and Y. T. Lee, Chem. Phys. Lett. 395, 311 ͑2004͒.
R. L. Nuttall, A. H. Laufer, and M. V. Kilday, J. Chem. Thermodyn. 3,
J. P. Cole and G. G. Balint-Kurti, J. Chem. Phys. 119, 6003 ͑2003͒.
E. J. Feltham, R. H. Qaadiri, E. Cottrill, P. A. Cook, J. P. Cole, G. G.
Balint-Kurti, and M. N. R. Ashfold, J. Chem. Phys. 119, 6017 ͑2003͒.
M. Castillejo, S. Couris, E. Lane, M. Martin, and J. Ruiz, Chem. Phys.
1
1
1
2
7
8
9
0
1
67 ͑1971͒.
4
5
R. N. Dixon, D. W. Huang, X. F. Yang, S. Harich, J. J. Lin, and X. Yang,
Science 285, 1249 ͑1999͒.
G. J. Fujimoto, M. E. Umstead, and M. C. Lin, Chem. Phys. 65, 197
2
32, 353 ͑1998͒.
C. C. Hayden, D. M. Neumark, K. Shobatake, R. K. Sparks, and Y. T.
͑
1982͒.
Lee, J. Chem. Phys. 76, 3607 ͑1982͒.
6
7
B. I. Sonobe and R. N. Rosenfeld, J. Am. Chem. Soc. 105, 7528 ͑1983͒.
E. J. Feltham, R. H. Qadiri, E. E. H. Cottrill, P. A. Cook, J. P. Cole, G. G.
Balint-Kurti, and M. N. R. AshfoldJ. Chem. Phys. 119, 6017 ͑2003͒.
J. Shu, J. J. Lin, Y. T. Lee, and X. Yang, J. Am. Chem. Soc. 123, 322
͑2001͒.
W. C. Price, J. P. Teegan, and A. D. Walsh, J. Chem. Soc. 1951, 920.
M. Drabbels, C. G. Morgan, D. S. McGuire, and A. M. Wodtke, J. Chem.
Phys. 102, 611 ͑1995͒.
21
8
22
C. G. Morgan, M. Drabbels, and A. M. Wodtke, J. Chem. Phys. 104,
7460 ͑1996͒.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
09.183.185.254 On: Sun, 23 Nov 2014 05:04:06
2