Kinetics for the recombination of phenyl radicals

Article abstract of DOI:10.1021/jp961569i

The rate constant for the C₆H₅ + C₆H₅ recombination reaction has been determined in the temperature range 300-500 K using a laser photolysis/mass spectrometric technique. The result is represented by k₁ = (1.39 ± 0.11) × 10¹³e^-(56±36)/T cm³/(mol s). In addition, the rate constant for the C₆H₅ + C₆H₅NO association reaction was found to be k₄ = (4.90 ± 0.19) × 10¹²e^(34±16)/T cm³/(mol s) by the mass balance of the initial concentration of C₆H₅ radicals. Using the result of k₁, previous kinetic data for C₆H₅ reactions determined by the conventional relative rate method were reanalyzed.

Full text of DOI:10.1021/jp961569i

14
J. Phys. Chem. A 1997, 101, 14-18
Kinetics for the Recombination of Phenyl Radicals
J. Park and M. C. Lin*
Department of Chemistry, Emory UniVersity, Atlanta, Georgia 30322
ReceiVed: May 30, 1996; In Final Form: October 8, 1996X
The rate constant for the C6H5 + C6H5 recombination reaction has been determined in the temperature range
300-500 K using a laser photolysis/mass spectrometric technique. The result is represented by k1 ) (1.39
( 0.11) × 1013e-(56(36)/T cm3/(mol s). In addition, the rate constant for the C6H5 + C6H5NO association
reaction was found to be k4 ) (4.90 ( 0.19) × 1012e(34(16)/T cm3/(mol s) by the mass balance of the initial
concentration of C6H5 radicals. Using the result of k1, previous kinetic data for C6H5 reactions determined
by the conventional relative rate method were reanalyzed.
Introduction
Phenyl radical is one of the most important reactive species
in the combustion of hydrocarbons, particularly in relation to
the formation of polycyclic aromatic hydrocarbons (PAH’s) and
the combustion of lead-free gasoline in which small aromatics
are used as additives.1-5 Prior to our recent use of the cavity-
ring-down (CRD) method6-15 for direct determination of rate
constants of various C6H5 reactions in the gas phase, most
kinetic data were analyzed by using the recombination of phenyl
radicals as a reference process:16-19
k1
C6H5 + C6H5
98 C12H10 (biphenyl)
(1)
Experimentally, the products of C6H5 metathetical reactions, for
example C6H6 from its reaction with H2,
k2
C6H5 + H2
98 C6H6 + H
(2)
Figure 1. Typical time-resolved mass spectrometric transient signals
of C12H10 and C6H5NO. See text for explanation.
were determined together with biphenyl; the rate constant for
the abstract process was then calculated with the much-used
relationship16-19
using the laser photolysis/high-pressure mass spectrometric
sampling system recently employed for product branching
studies of NH2 reactions with NO20 and NO2.21 The configu-
ration of the quartz reaction tube, which has a 120 µm conical
supersonic sampling hole at the center of the tube, is similar to
that described by Saalfeld and co-workers,22,23 and the coupling
of the photodissociation excimer laser with the reactor is
essentially the same as that used by Gutman and collabora-
tors.24,25 A schematic diagram of the apparatus and the
procedure of product measurements have been presented in
greater detail in the preceding article.26
The C6H5 radical was generated by the photolysis of C6H5NO
(nitrosobenzene) at 248 nm;6-15 the conversion of C6H5NO at
this wavelength with an unfocused, 30-50 mJ KrF laser beam
was in the range 20-40% with no evidence of secondary
photofragmentation of C6H5. The initial concentration of C6H5
in each experimental run was determined reproducibly from the
depletion of C6H5NO in the presence of an excess amount of
HBr diluted in He. The known fast exchange reaction,9 C6H5
+ HBr f C6H6 + Br, prevents the facile recombination reaction
C6H5 + NO f C6H5NO8 and other C6H5 radical reactions from
occurring so as to give a correct calculation of the initial
concentration of C6H5, [C6H5]0. The typical time-resolved
transient signals are shown in Figure 1. The rise of the C12H10
signal is attributable to the formation of C12H10 from the
recombination reaction of C6H5 and the decay of C6H5NO signal
k2 ) (k1/[C12H10])1/2[C6H6]/[H2]
using an assumed “reasonable” value for k1. However, the value
of k1 has been chronologically reduced from 1 × 1014 (ref 17)
to 1 × 1013 (ref 19) to 3 × 1012 cm3/(mol s) in most recent
analyses of high-temperature kinetic data by Stein and co-
workers.18 This historic change reduces the values of k2’s by
as much as 580%.
In view of the uncertainty in k1 and its pronounced effect on
the magnitude of many rate constants measured to date for C6H5
reactions (some of which are too slow to be determined directly
by the CRD technique, e.g., C6H5 + CH4), we have carried out
a series of kinetic measurements for k1 using a laser photolysis-
mass spectrometric technique.20,21 The results of this study for
k1 and the reanalyzed kinetic data for many of the C6H5 reactions
determined by the conventional relative rate method are reported
herein.
Experimental Section
The rate constant for the recombination of C6H5 radicals has
been measured at five temperatures between 300 and 500 K
* Corresponding author. e-mail address: chemmcl@emory.edu.
X Abstract published in AdVance ACS Abstracts, December 1, 1996.
S1089-5639(96)01569-1 CCC: $14.00 © 1997 American Chemical Society

Kinetics for the Recombination of Phenyl Radicals
J. Phys. Chem. A, Vol. 101, No. 1, 1997 15
TABLE 1: Typical Reaction Conditionsa and Rate Constantsb at Selected Temperatures Studied
T (K)
P
[C6H5NO]0
[NO]0
[C6H5]0
[C12H10]tc
[C6H5NO]tc
[C12H10NO]td
k1
k4
300
6620
6650
6700
6770
6620
6620
6620
6620
6620
6620
6620
6620
6620
6840
6840
6840
6840
6840
6880
6990
7110
7220
7320
6.21
6.09
6.06
6.02
5.68
5.59
5.52
5.43
5.37
5.18
5.01
4.89
4.79
5.75
5.60
5.42
5.28
5.17
5.95
5.87
5.80
5.72
5.67
12.21
17.13
19.91
23.49
14.28
17.54
19.88
23.07
25.41
20.44
26.86
31.55
35.50
15.25
20.74
27.29
32.56
36.75
14.85
21.18
27.98
34.21
39.34
2.02
1.98
1.97
1.96
2.51
2.48
2.45
2.41
2.38
2.77
2.68
2.61
2.56
2.69
2.62
2.53
2.47
2.41
2.55
2.52
2.48
2.45
2.43
0.106
0.082
0.070
0.061
0.183
0.158
0.143
0.132
0.118
0.187
0.159
0.135
0.116
0.266
0.201
0.156
0.121
0.122
0.236
0.204
0.159
0.144
0.133
7.283
7.315
7.364
7.401
6.880
6.934
7.027
6.985
6.956
6.783
6.711
6.670
6.616
7.000
7.013
6.942
6.893
6.796
7.010
7.190
7.270
7.313
7.346
0.367
0.312
0.279
0.218
0.473
0.405
0.327
0.295
0.277
0.394
0.329
0.282
0.249
0.451
0.400
0.350
0.304
0.269
0.508
0.396
0.346
0.288
0.246
1.012
1.073
1.036
1.034
1.145
1.187
1.186
1.269
1.257
1.222
1.265
1.271
1.098
1.331
1.289
1.320
1.230
1.438
1.311
1.341
1.173
1.424
1.486
0.486
0.574
0.580
0.514
0.548
0.558
0.492
0.520
0.540
0.497
0.560
0.562
0.561
0.425
0.494
0.569
0.591
0.599
0.447
0.462
0.507
0.502
0.496
353
405
442
500
a The units of total pressure and all concentrations are in mTorr. [X]0 represents the concentration of species X immediately after photolysis, t
) 0. b k is in units of 1013 cm3/(mol s). c The signal amplitudes were taken at t ) 10 ms in their plateau regions. d The yields of biphenyl nitroxide
were calculated by eq 9. See text for explanation.
indicates the depletion of C6H5NO by photolysis. A detailed
explanation will be given later.
benzene measured in the plateau region of the concentration
time profiles, typically t g 2 ms. [C6H5NO]0 is the concentra-
tion of nitrosobenzene measured after photolysis in the presence
of excess HBr. Accordingly, [C6H5NO]0 + [C6H5]0 represents
the concentration of nitrosobenzene before photolysis.
The apparent loss of the C6H5 radical at time t, as mentioned
above, is attributable to the association reaction
The rate constant for the recombination of C6H5 radicals was
determined by measuring the absolute yields of biphenyl in the
presence of varying amounts of NO, which competes with the
recombination process. The absolute concentration of C12H10
and the regenerated concentration C6H5NO formed by the
competing reactions
C6H5 + C6H5NO
9
48 (C6H5)2NO
(4)
C6H5 + C6H5
9
18 C12H10
(1)
(3)
producing the biphenyl nitroxide radical, which had been
previously detected in solution at room temperature.28 Our
search for m/z 184 indeed revealed the presence of the species,
which was not present before or after photolysis in the presence
of the excess amount of HBr.
C6H5 + NO
9
38 C6H5NO
can be calibrated with prepared mixtures. For C12H10, the
saturated vapor pressure at room temperature (297 K) diluted
with 50 Torr of He was used as the calibration sample. For
C6H5NO, varying known amounts of the molecule were diluted
with 100 Torr of He and were used as calibration mixtures after
overnight mixing.
All chemicals used in the present study (C6H5NO, C12H10,
and HBr) were obtained from Aldrich. HBr, which is known
to contain H2 impurity, was purified by trap-to-trap distillation.
C6H5NO was purified by recrystallization using ethanol as
solvent27 with subsequent vacuum distillation to remove the
solvent. The C12H10, which was determined to have 11.0 mTorr
vapor pressure at 297 K, was stored in a 5 L Pyrex bulb and
was degassed by prolonged diffusion pumping. He (99.999%
purity) acquired from Specialty Gases was used without further
purification.
In order to account for the mass balance of the C6H5, we
write
∆[C6H5] ) [C6H5]0 - 2[C12H10]t -
([C6H5NO]t - [C6H5NO]0) (5)
where ∆[C6H5] is the disappearance of C6H5 through reaction
4 which consumes both C6H5 and C6H5NO (see Figure 1).
Again, by mass balance,
[C6H5]0 ) 2[C12H10]t + [C6H5NO]gain + [(C6H5)2NO]t (6)
and
[C6H5NO]t - [C6H5NO]0 ) [C6H5NO]gain - [C6H5NO]loss
Results
) [C6H5NO]gain - [(C6H5)2NO]t
(7)
The experimental conditions, a set of data and kinetically
modeled results, are summarized in Table 1. The results indicate
that the initial concentration of C6H5, [C6H5]0, determined by
the depletion of C6H5NO in the presence of an excess amount
of HBr ([HBr]/[C6H5] > 300), is always greater than the quantity
2[C12H10]t + ([C6H5NO]t - [C6H5NO]0), where [C12H10]t and
[C6H5NO]t are the concentrations of biphenyl and nitroso-
where [C6H5NO]gain is the formation of C6H5NO by reaction 4
and [C6H5NO]loss is the consumption of C6H5NO by reaction
4. Combining eqs 6 and 7 with eq 5, and noting that
[C6H5NO]loss is the same as [(C6H5)2NO]t, we obtain
∆[C6H5] ) 2[(C6H5)2NO]t
(8)

16 J. Phys. Chem. A, Vol. 101, No. 1, 1997
Park and Lin
Figure 3. Arrhenius plots for the rate constants of C6H5 + C6H5 (O)
and C6H5 + C6H5NO (b) reactions.
Figure 2. Concentrations of C6H5 and product yields as functions of
NO concentration: (3) C6H5, (]) C6H5NO, (b) C12H10 × 5; (O)
(C6H5)2NO. Curves are kinetically modeled values.
The present result, k1 ) 1.4 × 1013e-56/T cm3/(mol s), falls within
the range of values assumed, 1 × 1014-3 × 1012 cm3/(mol s),
over time.16-19 The value of k1 at 298 K, 1.2 × 1013 cm3/(mol
s), is close to those of alkyl radical recombination reactions.29
It deserves some speculation whether the small apparent
activation energy, 0.4 kcal/mol, exists. At present, the system
with 12 heavy atoms defies any reasonable attempt of quantita-
tive ab initio quantum calculations. In principle, the recombina-
tion reaction may take place by the following two paths via
singlet and/or triplet potential energy surfaces:
The mass balance for C6H5 is then
[C6H5]0 ) 2[C12H10]t + ([C6H5NO]t -
[C6H5NO]0) + 2[(C6H5)2NO]t
or
[(C6H5)2NO]t ) 1/2{[C6H5]0 - 2[C12H10]t -
[C6H5NO]t + [C6H5NO]0} (9)
direct association
C6H5 + C6H5 f C6H5‚‚C6H5 f C6H5sC6H5 (C12H10)
We kinetically modeled the yields of C12H10, C6H5NO, and
(C6H5)2NO at time t with the following three-step mechanism:
indirect association by addition-isomerization
C6H5 + C6H5
9
18 C12H10
9
38 C6H5NO
(1)
(3)
(4)
C6H5 + C6H5 f C6H5‚CHdCHCHdCCHdCH f
C6H5sCHCHCHdCCHdCH
C6H5 + NO
C6H5 + C6H5NO 9
48 (C6H5)2NO
H migration8 C6H5sC6H5 (C12H10)
by adjusting the values of k1 and k4 with the known rate constant
for reaction 3, k3 ) 2.7 × 1012e433/T cm3/(mol s).8 A typical
set of experimental and kinetically modeled results at 355 K of
the three product concentrations as functions of NO is presented
in Figure 2. The experimental yields of biphenyl nitroxide were
obtained by eq 9 using measured [C6H5]0, [C6H5NO]t, [C6H5-
NO]0, and [C12H10]t. In Figure 2, the kinetically modeled results
are shown as curves, which can quantitatively depict the
variation of C12H10, C6H5NO, and (C6H5)2NO with the con-
centration of NO using a reproducible set of k1 and k4 (see Table
1 also). The averaged values of k1 and k4 obtained from the
modeling of kinetic data covering five temperatures between
The direct, singlet state association at the radical sites of C6H5
is expected to occur with little or no activation barrier, whereas
the recombination by addition-isomerization is expected to have
a small activation energy similar to that in the C6H5 + C6H6 f
C12H11 reaction, which has an apparent activation energy of 4
kcal/mol18 (at low temperatures). Since the addition process is
also quite exothermic (∆H e -74 kcal/mol) due to the
formation of a strong C-C bond (∼110 kcal/mol) at the expense
of a fraction of the resonance energy (<36 kcal/mol), the internal
excitation in the adduct may be sufficient to bring about the
isomerization (H migration) process. A small contribution of
the addition-isomerization at higher temperatures may result
in the small overall activation energy observed.
Since the concentration of biphenyl was determined by
calibration at the m/z 154 parent ion peak, it may be affected
to some extent by the presence of biphenyl nitroxide with m/z
184. To our knowledge, the fragmentation pattern of (C6H5)2-
NO has not been experimentally measured. Accordingly, we
could only draw the conclusion from examining its analogous
compounds such as (C6H5)2NH, (C6H5)2CO, and C6H5NN(O)-
C6H5, whose fragmentation patterns have been determined and
reported in the literature.30 At the ionization energy employed
in the present study, 70 eV, all the aforementioned compounds
exhibit negligible ion abundances at m/z 154, typically e0.05
of the most abundant ions. Therefore, we assumed no contribu-
300 and 500 K are graphically presented in Figure 3.
A
weighted least-squares analysis of the data by convoluting the
8
reported error for k3 gave for reaction 1
k1 ) (1.39 ( 0.11) × 1013e-(56(33)/T cm3/(mol s)
(10)
and for reaction 4
k4 ) (4.90 ( 0.19) × 1012e(34(16)/T cm3/(mol s) (11)
Discussion
The rate constant for the recombination of C6H5 radicals
presented in Figure 3 constitutes the first determination of k1.

Kinetics for the Recombination of Phenyl Radicals
J. Phys. Chem. A, Vol. 101, No. 1, 1997 17
TABLE 2: Rate Constants of Several Abstraction Reactions
kinetic measurements by CRD, will be investigated in the near
future for direct comparison. For C6H5 reactions with C2H2
and C2H4, whose rate constants measured by Stein and col-
laborators above 1000 K using a Knudsen cell under low-
pressure conditions,18 have been shown to be consistent with
our calculated values by the RRKM theory fitted to our low-
temperature CRD data.11,14 Because the long extrapolation
covering several decades of k-values, the increase in the
reference rate constant from 3 × 1012 to 1.4 × 1013e-56/T cm3/
(mol s), amounting to about a factor of 2.4 at 1000 K, is not
expected to bring about any severe disagreement from our earlier
conclusion. However, this question will be examined when
additional kinetic data are acquired for the two reactions at
higher temperatures than have been achieved11,14 and analyzed
with the aid of high-level ab initio MO results.
Reevaluated with Our k1
reaction
T (K)
log (A/cm3/(mol s)) Ea(kcal/mol) ref
H2
CH4
453-623
453-623
550-680
550-680
583-680
550-680
453-773
1000-1330
1000-1330
1000-1330
10.63
10.85
11.56
11.46
11.06
11.26
9.83
14.02
12.82
12.92
6.7
7.7
11.3
6.9
8.7
6.5
5.4
10.3
6.4
a
a
b
b
b
b
a
c
c
c
i-C4H10
c-C3H6
CH3COC6H5
CF3H
C2H2
C2H4
C6H6
8.7
a Reference 16. b Reference 17; the originally reported rate constants
were evaluated with k ) 1 × 1014 cm3/(mol s). c Reference 18.
tion or contamination from (C6H5)2NO to our biphenyl con-
centration measurement.
Conclusions
The formation of biphenyl nitroxide and the average value
of the rate constant for its production, k4 ) 5.4 × 1012 cm3/
(mol s), appear to be reasonable. Dialkyl nitroxides are known
to be stable. For example, the first C-N bond in (CH3)2NO
has been calculated to be as strong as 43 kcal/mol by Melius
using the BAC-MP4 method.31 In fact, di-(t-C4H9)2NO is a
well-known radical trap which is commercially available and
is typically delivered in bottles.32
The reactions of alkyl radicals with nitrosoalkanes have been
investigated semiquantitatively by Lampe and co-workers33,34
using mass spectrometry. For CD3 + CD3NO, the rate constant
for the formation of dimethyl-d6 nitroxide was reported to have
a lower limit of 4 × 1012 cm3/(mol s) at room temperature,
while for C2H5 + C2H5NO, its lower limit was established as
1.4 × 1012 cm3/(mol s) at 329 K. These results are consistent
with our finding for C6H5 + C6H5NO, 5.4 × 1012 cm3/(mol s).
Possibility of Wall Effects. At present, the possibility of
wall effects on C6H5 kinetics cannot be quantitatively assessed.
However, for these fast phenyl reactions, such effects may be
negligible. For example, in our preceding paper on NH2 + NO,
which occurs with a rate comparable to the C6H5 recombination
reaction, we have demonstrated that coating the reactor with
concentrated phosphoric acid did not lead to measurable effects
on the values of its total rate constant and H2O-product
branching ratio at pressures as low as 2 Torr.
In the present work, we have measured for the first time the
rate constant for the recombination of C6H5 radicals using the
laser photolysis/mass spectrometric technique. The absolute
product yields of biphenyl and the increased formation of
C6H5NO over that determined immediately after photolysis as
functions of added NO concentrations have been carefully
measured by using standard mixtures. From the analysis of
mass balance, it was concluded and subsequently confirmed that
an additional reaction product, biphenyl nitroxide, was formed
in the reaction. Kinetic simulation of the measured yields of
biphenyl, nitrosobenzene, and the calculated amounts of bi-
phenyl nitroxide employing the known rate constant for C6H5
+ NO f C6H5NO at varying NO concentrations allowed us to
reproducibly obtain the rate constants for biphenyl and biphenyl
nitroxide formation, respectively:
k1 ) (1.39 ( 0.11) × 1013e-(56(33)/T cm3/(mol s)
k4 ) (4.90 ( 0.19) × 1012e+(34(16)/T cm3/(mol s)
We have also used our result for k1 to reevaluate the existing
rate constants previously calculated with assumed, grossly
different values of k1. The new Arrhenius parameters thus
obtained are summarized in Table 2 for future applications.
After we completed the phenyl kinetic measurement, we have
examined the possibility of wall effects on a well-studied
recombination reaction, CH3 + CH3. For several reaction
pressures ranging from 2 to 10 Torr with CH3COCH3 as the
radical source and He as carrier gas, the recombination rate
constant determined by the growth rate of C2H6 increases from
1.7 × 1013 to 2.1 × 1013 cm3/(mol s), independent of surface
coating. These pressure-dependent rate constants agree closely
with the values reported by Gutman, Pilling, and co-workers.35
Reevaluation of Rate Constants for Several Known C6H5
+ RH Reactions. Prior to our recent measurements of rate
constants for C6H5 reactions with the CRD method,6-15 about
a dozen rate constants for the simple abstraction reactions
Acknowledgment. The authors gratefully acknowledge the
support of this work by the Division of Chemical Sciences,
Office of Energy Sciences, DOE, under Contract DE-FGO5-
91ER14192. We also thank Dr. T. Yu for a recrystallized and
purified nitrosobenzene sample used in the present study.
References and Notes
(1) Glassman, I. Combustion, 2nd ed.; Academic Press: New York,
1986.
(2) Brezinsky, K. Prog. Energy Combust. Sci. 1986, 12, 1.
(3) Bittner, J. D.; Howard, J. B. 18th Symposium (International) on
Combustion; The Combustion Institute: Pittsburgh, PA, 1983; p 1105.
(4) Brezinsky, K.; Litzinger, T. A.; Glassman, I. Int. J. Chem. Kinet.
1984, 16, 1053.
(5) Sawyer, R. F. 24th Symposium (International) on Combustion; The
Combustion Institute: Pittsburgh, PA, 1992; p 1423.
(6) Yu, T.; Lin, M. C. J. Am. Chem. Soc. 1993, 115, 4371.
(7) Lin, M. C.; Yu, T. Int. J. Chem. Kinet. 1993, 25, 875.
(8) Yu, T.; Lin, M. C. J. Phys Chem. 1994, 98, 2105.
(9) Yu, T.; Lin, M. C. Int. J. Chem. Kinet. 1994, 26, 771.
(10) Yu, T.; Lin, M. C. J. Phys. Chem. 1994, 98, 9697.
(11) Yu, T.; Lin, M. C. Int. J. Chem. Kinet. 1994, 26, 1095.
(12) Yu, T.; Lin, M. C. J. Am. Chem. Soc. 1994, 116, 9571.
(13) Yu, T.; Mebel, A. M.; Lin, M. C. J. Phys. Org. Chem. 1995, 8, 47.
(14) Yu, T.; Lin, M. C. Combust. Flame 1995, 100,169.
(15) Yu, T.; Lin, M. C. J. Phys. Chem. 1995, 99, 8599.
(16) Fielding, W.; Pritchard, H. O. J. Phys. Chem. 1962, 66, 821.
C6H5 + RH f C6H6 + R
including C6H5 + H2 mentioned in the Introduction were
determined with reference to reaction 1, assuming a wide range
of k1 values, from 1 × 1014 to 3 × 1012 cm3/(mol s), as alluded
to earlier. In Table 2, we summarize these reactions with the
reevaluated Arrhenius parameters using our present result, k1
) 1.4 × 1013e-56/T cm3/(mol s).
Some of the reactions with lower activation energies, e.g.,
C6H5 + i-C4H10 and CH3COC6H5, which may be amenable to

18 J. Phys. Chem. A, Vol. 101, No. 1, 1997
Park and Lin
(17) Duncan, F. J.; Trotman-Dickenson, A. F. J. Chem. Soc. 1962, 4672.
(18) (a) Fahr, A.; Mallard, W. G.; Stein, S. E. 21st Symposium
(International) on Combustion; The Combustion Institute: Pittsburgh, PA,
1986; p 825. (b) Fahr, A.; Stein, S. E. Ibid., 1988; p 1023.
(19) Kerr, J. A.; Moss, S. J. Handbook of Bimolecular and Termolecular
Gas Reactions; CRC Press: Boca Raton, FL, 1981; Vol. I.
(20) Park, J.; Lin, M. C. J. Phys. Chem. 1996, 100, 3317.
(21) Park, J.; Lin, M. C. Mass-Spectrometric Determination of Product
Branching Probabilities in the NH2 + NO2 Reaction at Temperatures
between 300 and 990 K. Int. J. Chem. Kinet., in press.
(22) Wyatt, J. R.; DeCorpo, J. J.; McDowell, M. V.; Saalfeld, F. E.
ReV. Sci. Instrum. 1974, 45, 916.
(27) McFarland, J. W. Organic Laboratory Chemistry, C. V. Mosby,
St. Louis, MO, 1969.
(28) (a) Maruyama, K.; Tanikaga, R.; Goto, R. Bull. Chem. Soc. Jpn.
1964, 37, 1893. (b) Tanikaga, R. Bull. Chem. Soc. Jpn. 1969, 42, 210.
(29) Kerr, J. A.; Drew, R. M. Handbook of Bimolecular and Ter-
molecular Gas Reactions; CDC Press: Boca Raton, FL, 1987; Vol. III,
Part B.
(30) McLafferty, F. W.; Stauffer, D. B. The Wiley/NBS Registry of Mass
Spectral Data; John Wiley & Sons: New York, 1989; Vol. 1.
(31) Melius, C. F. BAC-MP4 Heats of Formation and Free Energies;
Sandia National Laboratories, Livermore, CA, April 25, 1993.
(32) Catalog Handbook of Fine Chemicals, Aldrich Chemical Co.:
Milwaukee, WI, 1994-1995; p 458.
(23) Wyatt, J. R.; DeCorpo, J. J.; McDowell, M. V.; Saalfeld, F. E. Int.
J. Mass Spectrom. Ion Phys. 1975, 16, 33.
(33) Maschke, A.; Shapiro, B. S.; Lampe, F. W. J. Am. Chem. Soc. 1964,
86, 1929.
(34) Tan, H.-S.; Lampe, F. W. J. Phys. Chem. 1972, 76, 3303.
(35) Slagle, I. R.; Gutman, D.; Davies, J. W.; Pilling, M. J. J. Phys.
Chem. 1988, 92, 2455.
(24) Slagle, I. R.; Gutman, D. J. Am. Chem. Soc. 1985, 107, 5342.
(25) Russell, J. J.; Seetula, J. A.; Gutman, D. J. Am. Chem. Soc. 1988,
110, 3092.
(26) Park, J.; Lin, M. C. J. Phys. Chem. 1997, 101, 5.