Infrared spectroscopic studies on photolysis of methyl iodide and its clusters in solid parahydrogen

Article abstract of DOI:10.1063/1.469763

Methyl iodide is trapped as the monomer and as clusters in the parahydrogen, known as a quantum crystal, at temperatures below about 8 K.UV illumination of the deposited sample at about 5 K causes the dispersal of clusters and the production of the methyl radical, methane, and ethane as evidenced by their infrared absorption spectra.Thermal annealing of the photolyzed sample at temperatures up to 11 K results in the disappearance of the methyl radical, the enhancement of ethane, and the regeneration of methyl iodide.When the initial concentration of the iodide is small, the clusters in the deposited sample are suppressed.For such a sample the UV excitation produces the methyl radical and methane but the formation of ethane is negligibly small.Relevance of the present work to studies of photolysis in gaseous clusters of methyl iodide is discussed.

Full text of DOI:10.1063/1.469763

Infrared spectroscopic studies on photolysis of methyl iodide and its clusters in solid
parahydrogen
Takamasa Momose, Masaaki Miki, Mikio Uchida, Takayuki Shimizu, Isamu Yoshizawa, and Tadamasa Shida
Citation: The Journal of Chemical Physics 103, 1400 (1995); doi: 10.1063/1.469763
View online: http://dx.doi.org/10.1063/1.469763
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Infrared spectroscopic studies on photolysis of methyl iodide and its
clusters in solid parahydrogen
Takamasa Momose, Masaaki Miki, Mikio Uchida, Takayuki Shimizu, Isamu Yoshizawa,
and Tadamasa Shida
Department of Chemistry, Faculty of Science, Kyoto University, Kyoto 606-01, Japan
͑Received 14 April 1995; accepted 21 April 1995͒
Methyl iodide is trapped as the monomer and as clusters in the parahydrogen, known as a quantum
crystal, at temperatures below about 8 K. UV illumination of the deposited sample at about 5 K
causes the dispersal of clusters and the production of the methyl radical, methane, and ethane as
evidenced by their infrared absorption spectra. Thermal annealing of the photolyzed sample at
temperatures up to 11 K results in the disappearance of the methyl radical, the enhancement of
ethane, and the regeneration of methyl iodide. When the initial concentration of the iodide is small,
the clusters in the deposited sample are suppressed. For such a sample the UV excitation produces
the methyl radical and methane but the formation of ethane is negligibly small. Relevance of the
present work to studies of photolysis in gaseous clusters of methyl iodide is discussed. © 1995
American Institute of Physics.
I. INTRODUCTION
The optical measurement was performed by a Nicolet
FTIR spectrometer ͑Magna 750͒ with a CaF2 beamsplitter
and a MCT ͑HgCdTe͒ detector with a resolution of 0.25
cmϪ1. The measurements before and after the UV illumina-
tion described below were made at 4.80Ϯ0.05 K. The UV
illumination was carried out by using a 20 W mercury lamp
which was placed directly in front of the outermost CaF2
window of the cryostat. To see the effect of thermal anneal-
ing the photolyzed sample was kept at temperatures between
4.8 and 11.0 K for 15 min with an accuracy of Ϯ0.1 K, and
then the optical measurement was carried out at each el-
evated temperature.
Methyl iodide is one of the prominent molecules in mo-
lecular photophysics and chemistry because it has provided
information on topics of fundamental importance such as the
branching into two channels separated by the spin–orbit
interaction,1 the real-time dynamics of the C–I bond
scission,2–4 and the internal energy distribution of the photo-
dissociated methyl radical in the vibrational5–10 and the ro-
tational energy regimes.11–14 Also, recent interest in possible
new photochemical reactions in clusters15 has attracted atten-
tion to the methyl iodide cluster in molecular beams.16–24
Meanwhile, a new high-resolution matrix-isolation spec-
troscopy using the solid parahydrogen as the matrix has been
launched recently by Oka and co-workers. They have been
studying relatively simple molecules such as orthohydrogen
and deuterated hydrogens.25–31 The new matrix has several
salient features favorable for high-resolution spectroscopy.
We attempt to apply the new technique for the study of mol-
ecules of chemical interest such as methyl iodide. The
present work is the first of a series of studies using the solid
parahydrogen as a new matrix.
III. EXPERIMENTAL RESULTS
Spectra I–IV in Figs. 1 and 2 are for a relatively con-
centrated sample. Spectrum I was observed immediately af-
ter lowering of the temperature of the deposited sample to
4.80 K. Spectrum II is the same as I after a succeeding 150
min UV illumination at 4.80 K. Spectra III and IV are the
same as II after successive elevation of temperature of the
illuminated sample to 7.0 and 8.0 K, respectively. Spectral
measurements were also made at other temperatures up to
11.0 K to obtain continuously changing spectra which are not
shown in the figures to avoid congestion. The scales of the
ordinate are arbitrary but are common to the four spectra in
each figure. They are vertically displaced for clarity. All the
numbers on the abscissa and in the text are in units of cmϪ1
throughout the present paper.
II. EXPERIMENT
Ultrahigh purity ͑Ͼ99.999 95%͒ normal hydrogen gas
was transferred to a ferric oxide ortho–para converting cata-
lyst at ϳ14.3 K for about 1.5 h to obtain parahydrogen with
a purity of 99.9% as estimated by the intensity of the funda-
mental vibrational bands of orthohydrogen.31 Commercial
methyl iodide ͑Nacalai tesque, Inc.͒ was used as received.
The admixed gas of methyl iodide in parahydrogen with a
concentration of 0.005%–0.01% was introduced into a cop-
per cell which was attached to the bottom of a cryostat. The
inner diameter and the path length of the optical cell were 2
and 3 cm, respectively. Slightly wedged CaF2 windows of a
thickness of ϳ2 mm were attached to both ends of the cell
via indium gaskets. An optically transparent solid sample
was grown in the cell by continuously flowing the gas into
the cell at about 7.7 K, typically in 1 h.
The essential features of spectra I–IV are summarized as
follows:
Spectrum I: The bands at 3060–3040, 2965–2940, 2850,
and 2825–2815 in Fig. 1 and those at 1440–1420, 1410–
1395, and 1250–1235 in Fig. 2 are comparable with the re-
ported bands of methyl iodide in a neon matrix ͑Table I of
Ref. 32͒ which are reproduced below with the qualitative
description for the intensity as strong ͑s͒, medium ͑m͒, and
weak ͑w͒; 3055 ͑m͒, 2965 ͑s͒, 2855 ͑w͒, and 2830 ͑m͒ for
Fig. 1 and 1435 ͑s͒, 1409 ͑m͒, and 1249 ͑s͒ for Fig. 2. In
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Momose et al.: Photolysis of methyl iodide
1401
FIG. 1. Infrared absorption spectra of methyl iodide in solid parahydrogen, 3200–2750 cmϪ1. ͑I͒ As deposited at 4.8 K. ͑II͒ Same as I after a 150 min UV
illumination at 4.8 K. ͑III͒ Same as II measured at 7.0 K. ͑IV͒ Same as II measured at 8.0 K. We have measured the spectra at various temperatures up to 11
K to obtain intermediate spectral patterns but they are omitted to avoid congestion. The insets at the bottom and the top of the figure are for methane and
ethane in solid parahydrogen at 4.8–4.9 K, respectively. The symbols, R, I, M, and E stand for the methyl radical, methyl iodide, methane, and ethane. They
are indicated for convenience of identifying the absorption bands.
addition to the above seven absorption bands we observed a
weak band at 2485–2465 which apparently corresponds to
the one at 2496 reported for the neon matrix.32 This band,
considered to be the first overtone of the band at 1250–1235,
is omitted for the sake of space saving. The omission does
not affect the essential argument which follows. The numer-
ous downward spikes in the region of 1450–1360 of Fig. 2
are due to water vapor in the optical path and should be
ignored. On account of the fair agreement of the bands in
Figs. 1 and 2 with those reported for the neon matrix32 and of
the internal consistency in the spectral analysis to be pre-
sented below all the band systems enumerated above are as-
signed to methyl iodide.
Spectrum II: The spectral changes upon the UV illumi-
nation are remarkable and extensive. They can be classified
into the following three groups: R, M, and E. ͑These symbols
stand for the methyl rគadical, mគ ethane, and eគthane and these
three spectral changes will be shown to be related to these
three species.͒
3040–3000 and 1320–1295 which are found to behave in
common upon photo and thermal treatments as described
below.
Group E: Another new set of broad bands appears at
2985–2965 ͑s͒, 2960–2930 ͑weak and broad͒, 2923 ͑weak
but relatively sharp͒, and 2890–2870 ͑medium and partially
structured͒ in Fig. 1.
Besides the above three types of spectral changes we
note that the bands assigned to methyl iodide in spectrum I
and designated with I, which stands for the iodide, show a
general tendency to be sharpened with the loss of the broad
wing on the lower energy side. To be specific, the four bands
of spectrum I in Fig. 1 change to those showing a sharp peak
at 3057.6, 2965.2, 2853.1, and 2826.3. Similarly, the two
bands of spectrum I in Fig. 2 change to a small peak at
1432.6 superposing on a low ‘‘terrace’’ at ϳ1440–1425 and
another small peak at 1407.1. Finally, the partially structured
bands at 1250–1235 of spectrum I in Fig. 2 collapse into the
single feature at 1248.6. These spectral changes will be dis-
cussed in connection with the monomer and the cluster of
methyl iodide ͑see Sec. IV B͒.
Group R: A new trio appears as a doublet at 3171.4/
3170.6 ͑s͒, 2780.1/2779.3 ͑w͒, and 1402.7/1401.6 ͑s͒. They
can be attributed to a common signal carrier because of their
same behavior on warming ͑see spectra III and IV͒.
Group M: Richly structured bands newly appear at
Spectra III and IV: The conspicuous doublet absorptions
of group R diminish quickly with rising temperature while
those of group M also decrease accompanying the growth of
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Momose et al.: Photolysis of methyl iodide
FIG. 2. Infrared absorption spectra of methyl iodide in solid parahydrogen, 1450–1230 cmϪ1. See caption for Fig. 1. The numerous signals except for the
meaningful absorptions described in Sec. III are due to the irrelevant water vapor in the optical path. The ‘‘emissive’’ and absorptive patterns of the signals
are due to the temporal fluctuation of the cancellation between the measurements of the background and the sample. The inset at the lower right corner is for
a methane/parahydrogen system at 4.8–4.9 K.
a broad band in the lower energy region. The approximate
maxima of the broad bands at the final stage of spectrum IV
are at about 3015 and 1304. The absorptions of group E in
spectrum II are enhanced slightly with the smearing of the
structures seen for the bands at 2985–2965 and at 2890–
2870.
Spectra I–III in Fig. 3 demonstrate representatively the
spectral change observed for a relatively dilute sample. Spec-
trum I is for the sample immediately after the lowering of
temperature to 4.80 K. Spectrum II is the same as I after a
240 min UV illumination at 4.80 K and measured at the same
temperature. Spectrum III is the same as II after elevating the
sample to 7.0 K and measured at the same temperature. Due
to the reduction of the amount of the methyl iodide the over-
all spectral intensity in Fig. 3 is suppressed compared with
the spectra in Figs. 1 and 2. However, the following spectral
changes are notable:
and 2 also appear in Fig. 3 with the relative abundance of M
over R. In contrast, the strong band at 2985–2965 of group E
observed in Fig. 1 appears only feebly in the narrower region
of 2985–2980. The other band of group R at 1402.7/1401.6
and the one at 1320–1295 of group M are also observed as in
Fig. 2, but they are not shown to avoid redundancy. Notice
that the band at 2965–2955 seen in spectrum I of Fig. 3
disappears almost completely in spectrum II.
Spectrum III: The doublets of group R are reduced re-
markably as in Figs. 1 and 2 while the band at 2965–2955 in
spectrum I of Fig. 3 seems to have recovered slightly as
revealed by a small peak at about 2965.
IV. DISCUSSION
A. Spectral assignment
The spectra of group R are associated with the methyl
radical because the two strong doublets at 3171.4/3170.6 and
1402.7/1401.6 are reasonably close to the absorptions of the
methyl radical at 3162 ͑␯ ͒ and 1396 ͑␯ ͒ in a neon matrix
Spectrum I: The absorption band corresponding to that at
2965–2940 in spectrum I of Fig. 1 is sharpened by losing the
broad shoulder on the low energy side is compressed into a
narrower range of 2965–2955. At the same time the multip-
let structure is more pronounced than that on the band at
2965–2940 in spectrum I of Fig. 1.
3
4
͓Table II of Ref. 32, apparently the number of 1398 in Table
II should read 1396 in reference to Table VI͔ and at 3150 and
1385 in an argon matrix.33 They should also be compared
with the absorption of the radical in the gas phase. The band
Spectrum II: The doublet at 3171.4/3170.6 of group R
and the band at 3040–3000 of group M observed in Figs. 1
origin for the ␯ ͑the in-plane-degenerate CH stretch͒ band is
3
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Momose et al.: Photolysis of methyl iodide
1403
FIG. 3. Infrared absorption spectra of methyl iodide in solid parahydrogen, 3200–2750 cmϪ1. The spectra in this figure are for a sample in which methyl
iodide molecules are better isolated than those for a sample giving the spectra in Figs. 1 and 2. ͑I͒ As deposited at 4.8 K. ͑II͒ Same as after a 240 min UV
illumination at 4.8 K. ͑III͒ Same as II measured at 7.0 K.
determined to be 3160.8212͑12͒ ͑Ref. 34͒ while the ␯ band
has not been detected. The very weak absorptions at 2780.1/
2779.3 barely seen in spectrum II of Fig. 1 are regarded as
present work for an ethane/parahydrogen system which are
shown in the upper insets of Fig. 1. It should be emphasized
that ethane is already produced at the stage of the UV illu-
mination at 4.8 K ͑see discussion on photochemistry below͒.
In concluding this subsection we can summarize that the
spectral changes of R, M, and E in the previous section are
associated with the production of the methyl radical, meth-
ane, and ethane, all being induced upon the UV illumination.
4
the first overtone of the ␯ band which has not been previ-
4
ously reported to our knowledge. The considerable blue shift
of the absorptions in the solid hydrogen relative to the gas
phase and their doublet feature are a most interesting subject
to pursue. It is pertinent in this context to mention a recent
report of the ESR detection of the methyl radical in photo-
lyzed methyl iodide/parahydrogen mixture.35
B. Photochemistry
The spectra of group M are attributed to methane be-
cause we have observed quite comparable spectra for
methane/parahydrogen mixtures as shown in the lower insets
of Figs. 1 and 2. The characteristic structures on the two
band systems are indicative of the quantization of the rota-
tional levels of methane in the solid parahydrogen which will
be investigated in detail.36 At the moment it suffices to men-
tion that the systems at 3040–3000 and 1320–1295 are as-
signed to the ␯ ͑the asymmetric CH stretch͒ and the ␯ ͑the
In the present work the degree of isolation can be con-
trolled by changing both the initial concentration of methyl
iodide in the parahydrogen gas and the deposition tempera-
ture. A number of experiments with samples of varying de-
grees of isolation have led us to conclude that the samples
giving the spectra in Figs. 1 and 2 correspond to the case of
a medium degree of isolation which allows the coexistence
of the monomer and clusters, while in the sample for Fig. 3
the iodide is mostly isolated. The cluster absorption bands at
2965–2940 and 1250–1235 are featureless and are always
red shifted with respect to the sharp multiplets associated
with the monomer absorption bands. As for the nature of the
multiplets detailed analysis will be put forth following the
planned investigation of a similar multiplet feature observed
for the prototypical methane molecule.36 It is interesting to
3
4
degenerate CH bend͒ bands of the isolated methane
molecule.37
The new absorptions of group E are assigned to ethane
because they are in fair agreement with those observed for
ethane in a neon matrix at 2979 ͑s͒, 2947 ͑m͒, 2921 ͑w͒,
2888 ͑m͒, 2857 ͑w͒, and 2839 ͑w͒.32 Furthermore, they have
general resemblance to the absorptions recorded in the
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1404
Momose et al.: Photolysis of methyl iodide
note that the broad bands ascribed to the clusters transform
drastically into the sharp multiplets as is seen from the com-
parison of spectra I and II in Figs. 1 and 2. The change
indicates that the absorption of the UV photon by the clusters
causes not only the photochemical processes to be discussed
below but also efficient dispersal of the clusters to the mono-
mer. The excess energy corresponding to the difference be-
tween the photon energy and the energy required for the
chemical processes may be dissipated translationally to
‘‘boil’’ the clusters14,16 and spatter methyl iodide molecules
into the bulk of the solid hydrogen which may be depicted as
a temporary jellylike medium to accept the spattered mol-
ecules and confines each of them quickly. This may be a
most unique property of the quantum solid of hydrogen.
A remarkable change upon the UV illumination common
to Figs. 1–3 ͑cf. spectrum II against I͒ is that methyl iodide
diminishes ͑in Figs. 1 and 2͒ or disappears completely ͑in
Fig. 3͒ to yield the absorption bands of the methyl radical
and methane which are denoted by R and M, respectively.
Thus, it is obvious that some of the methyl radicals are suf-
ficiently reactive to yield methane while the remainder are
trapped. Since the feature of spectrum I in Fig. 3 indicates
that methyl iodide is well isolated compared with the
samples giving the spectra in Figs. 1 and 2, the hydrogen
atom donor for the formation of methane must be among the
hydrogen molecules surrounding the photolyzed iodide. At
the same time, the concomitant appearance of the methyl
radical implies that the thermalized methyl radical at 4.80 K
does not abstract the hydrogen atom, at least appreciably, in
the time scale of the present work. We can summarize the
above statement by reactions ͑1͒–͑3͒ below where the aster-
isk indicates that the radical is epithermal and that the rate of
reaction ͑3͒ is immeasurably slow, although the possibility of
a slow tunneling reaction between the thermalized radical
and a hydrogen molecule cannot be ruled out,
CH I͒ ϩh␯→CH ϩCH ϩI ,
and/or
͑4͒
͑5͒
͑
3
2
3
3
2
CH I͒ ϩh␯→C ϩH ϩI .
͑
3
2
2
6
2
The major reasoning for reactions ͑4͒ and ͑5͒ is that the
iodine molecule is produced within 10 ps,17 carrying only a
very small fraction of the exoergicity of the reaction.22 How-
ever, direct evidence for either product, the radical or ethane,
has not been given. Contrastingly, the present work has pro-
vided definite spectral evidence for both of them. The forma-
tion of ethane by reaction ͑5͒ seems to be substantiated be-
cause the bands of group E are already observed at 4.8 K for
the UV illuminated sample containing the methyl iodide
clusters ͑see spectrum II of Figs. 1 and 2͒ but only negligibly
for the sample containing no clusters ͑see spectrum II of Fig.
3͒.
C. Thermochemistry
The changes from spectrum II to III and IV in Figs. 1
and 2 and the change from II to III in Fig. 3 plainly indicate
the thermally induced disappearance of the methyl radical
͑R͒ and the increase of ethane ͑E͒. Although the absorption
line shape of ethane is deformed with temperature, the inte-
grated intensity of the absorption of E continues to increase.
Thus, one may add the following recombination reaction
which proceeds between the near-lying radicals formed by
reaction ͑4͒:
CH3ϩCH3→C2H6.
͑6͒
The necessity of the proximity of the two radicals is sup-
ported by the fact that the formation of ethane in the dilute
sample, where reaction ͑4͒ is prohibitive, is negligibly small
͑cf. spectrum II of Fig. 3͒. The thermal acceleration of the
recombination implies that the reaction is not completely
barrier-free, which is reasonable in view of the possible cage
effect in the solid matrix.
Meanwhile, the small recovery of methyl iodide in spec-
trum III of Fig. 3 may be attributed to the geminate recom-
bination of the iodine atom of reaction ͑1͒ with the counter-
part radical which has failed to induce reaction ͑2͒. Thus, we
add the following recombination also:
*
CH3Iϩh␯→CH3 ϩI,
͑1͒
͑2͒
͑3͒
*
CH3 ϩH2→CH4ϩH,
CH3ϩH2→CH4ϩH.
We note that the photon energy ͑ϳ4.9 eV͒ amply exceeds the
dissociation energy of the C–I bond ͑ϳ2.3 eV͒ to permit the
methyl radical being epithermal.
CH3ϩI→CH3I.
͑7͒
Another remarkable difference between Figs. 1 and 2 vs
Fig. 3 is that the photo-induced production of ethane in the
dilute sample is negligibly small ͑compare spectrum II of
Fig. 1 with spectrum II of Fig. 3͒. This indicates that the
formation of ethane is closely related to the initial clustering
of methyl iodide dominant in the concentrated sample.
Despite the difference of the present system of the solid
parahydrogen from the familiar system of jet-cooled molecu-
lar beams,16–24 we note some relevance between the two
systems from the viewpoint of the photochemical reactions
therein; studies of the valence excitation of gaseous methyl
iodide clusters in the molecular beam have disclosed ‘‘new’’
chemistry23 in which the iodine molecule is supposed to be
produced from the photoexcited dimer by an unusual con-
certed mechanism as summarized in reactions ͑4͒ and ͑5͒,
It is to be noted that the methyl radical survives at 4.8 K
for longer than 10 h. Thus, the recombination reactions ͑6͒
and ͑7͒ must be immeasurably slow at 4.8 K but start to be
observed at temperatures higher by only a few kelvins. Such
a sensitivity of the reactions to the temperature is quite re-
markable.
The three stable species, i.e., methyl iodide, methane,
and ethane, present in the photolyzed sample are considered
to be susceptible to aggregation by thermally induced diffu-
sion as revealed by the loss of the band structures and/or by
the red shift of the newly appearing broad bands ͑see Figs. 1
and 2͒. We note that the thermal expansion of the solid
parahydrogen increases sharply at temperatures above about
7 K.38 The stress caused by the increase in the thermal ex-
pansion may ease the diffusion of the molecules for aggre-
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Momose et al.: Photolysis of methyl iodide
1405
gation. In the case of ethane, however, both the loss of the
structure and the spectral shift are small compared with
methane and methyl iodide. It is also noted that the absorp-
tions ascribed to ethane in spectra II–IV of Fig. 1 are con-
siderably different from the absorptions of the ethane/
parahydrogen system shown in the inset of Fig. 1. In this
latter system ethane is not considered to be well isolated,
whereas the ethane giving the absorptions in spectra II–IV of
Fig. 1 should be isolated from another ethane molecule by
virtue of the mechanism of reaction ͑5͒. This difference of
the environment of ethane in the two systems is regarded as
responsible for the difference of the spectral line shape.
It must be stressed that the above argument is based on
the presumption that the reactions in the gaseous and in the
solid parahydrogen are essentially the same. To endorse the
assumption it is desirable to detect iodine molecules pro-
duced simultaneously with ethane and the methyl radical in
our system. We are now planning such experiments.
8 M. D. Barry and P. A. Gorry, Mol. Phys. 52, 461 ͑1984͒.
9 D. Imre, J. L. Kinsey, A. Asinha, and J. Krenos, J. Phys. Chem. 88, 3956
͑1984͒.
10 T. Suzuki, H. Kanamori, and E. Hirota, J. Chem. Phys. 94, 6607 ͑1991͒.
11 I. Powis and J. F. Black, J. Phys. Chem. 93, 2461 ͑1989͒.
12 R. O. Loo, H. P. Haerri, G. E. Hall, and P. L. Houston, J. Chem. Phys. 90,
4222 ͑1989͒.
13 D. W. Chandler, J. W. Thoman, Jr., M. H. M. Jassen, and D. H. Parker,
Chem. Phys. Lett. 156, 151 ͑1989͒.
14 M. Zahedi, J. A. Harrison, and J. W. Nibler, J. Chem. Phys. 100, 4043
͑1994͒.
15 R. B. Gerber, A. B. McCoy, and A. Garcia-Vela, Annu. Rev. Phys. Chem.
45, 275 ͑1994͒.
16 S. P. Sapers and V. Vaida, J. Chem. Phys. 88, 3638 ͑1988͒.
17 J. A. Syage and J. Steadman, Chem. Phys. Lett. 166, 159 ͑1990͒.
18 P. G. Wang, Y. P. Zhang, C. J. Ruggle, and L. D. Ziegler, J. Chem. Phys.
92, 2806 ͑1990͒.
19 D. J. Donaldson, V. Vaida, and R. Naaman, J. Chem. Phys. 87, 2522
͑1987͒.
20 V. Vaida, D. J. Donaldson, S. P. Sapers, R. Naaman, and M. S. Child, J.
Phys. Chem. 93, 513 ͑1989͒.
21 V. Vaida, D. J. Donaldson, S. P. Sapers, and R. Naaman, J. Chem. Soc.
Faraday Trans. 86, 2043 ͑1990͒.
22 Y. B. Fan and D. J. Donaldson, J. Phys. Chem. 96, 19 ͑1992͒.
23 Y. B. Fan and D. J. Donaldson, J. Chem. Phys. 97, 189 ͑1992͒.
24 Y. B. Fan, K. L. Randall, and D. J. Donaldson, J. Chem. Phys. 98, 4700
͑1993͒.
ACKNOWLEDGMENTS
The authors are most grateful to Professors Eizi Hirota
and Takeshi Oka for their encouragement and invaluable
concern for this work. Marry-Frances Jagod read the manu-
script and suggested modifications to the style. The work was
supported by the Grants-in-Aid for Scientific Research on
Priority Areas No. 05237105 and the Grant ͑C͒ No. 6640649
of the Ministry of Education, Science, and Culture, Japan.
Also, the support of the Toray Science Foundation, the Shi-
madzu Science Foundation, and the Sumitomo Foundation
are greatly appreciated.
25 T. Oka, Annu. Rev. Phys. Chem. 44, 299 ͑1993͒.
26 D. P. Weliky, T. J. Byers, K. E. Kerr, T. Momose, R. M. Dickson, and T.
Oka, Appl. Phys. B 59, 265 ͑1994͒.
27 M. Okumura, M-C. Chan, and T. Oka, Phys. Rev. Lett. 62, 32 ͑1989͒.
28 M-C. Chan, M. Okumura, C. M. Gabrys, L-W. Xu, B. D. Rehfuss, and T.
Oka, Phys. Rev. Lett. 66, 2060 ͑1991͒.
29 T. Momose, D. P. Weliky, and T. Oka, J. Mol. Spectrosc. 153, 760 ͑1992͒.
30 K. E. Kerr, T. Momose, D. P. Weliky, C. M. Gabrys, and T. Oka, Phys.
Rev. Lett. 72, 3957 ͑1994͒.
31 M-C. Chan, S. S. Lee, M. Okumura, and T. Oka, J. Chem. Phys. 95, 88
͑1991͒.
32 A. Snelson, J. Phys. Chem. 74, 537 ͑1970͒.
33 J. Pacansky and J. Bargon, J. Am. Chem. Soc. 97, 6869 ͑1975͒.
34 T. Amano, P. F. Bernath, C. Yamada, Y. Endo, and E. Hirota, J. Chem.
Phys. 77, 5284 ͑1982͒.
1 Y. Amatatsu and K. Morokuma, J. Chem. Phys. 94, 4858 ͑1991͒, and
references cited therein.
2 J. L. Knee, L. R. Khundkar, and A. H. Zewail, J. Chem. Phys. 83, 1996
͑1985͒.
35 T. Miyazaki, K. Yamamoto, and J. Arai, Chem. Phys. Lett. 219, 405
͑1994͒.
3 L. R. Khundkar and A. H. Zewail, Chem. Phys. Lett. 142, 426 ͑1987͒.
4 M. Tadjeddine, J. P. Flament, and C. Teichteil, Chem. Phys. 118, 45
͑1987͒.
36 The subject will be investigated jointly by the groups in Chicago ͑T. Oka͒
and Kyoto.
37 G. Herzberg, Molecular Spectra and Molecular Structure II. Infrared and
Raman Spectra of Polyatomic Molecules ͑Krieger, Malabar, FL, 1991͒, p.
306.
5 R. K. Sparks, K. Shobatake, L. R. Carlson, and Y. T. Lee, J. Chem. Phys.
75, 3838 ͑1981͒.
6 H. W. Hermann and S. R. Leone, J. Chem. Phys. 76, 4759 ͑1982͒.
7 G. N. A. van Veen, T. Baller, A. E. de Vries, and N. J. A. van Veen, Chem.
Phys. 87, 405 ͑1984͒.
38 P. C. Souers, Hydrogen Properties for Fusion Energy ͑University of Cali-
fornia, Berkeley, 1986͒, p. 79.
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