Chemical Physics 282 (2002) 305–314
www.elsevier.com/locate/chemphys
Ab initio and RRKM calculations for the
decomposition channels of CH3OBr and BrCH2OH
Demetrios K. Papayannis, Evangelos Drougas, Agnie M. Kosmas *
Physical Chemistry Laboratory, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
Received 8 March 2002
Abstract
Quantum mechanical and RRKM calculations are carried out to study the potential energy surface and the kinetics for
the six most important decomposition channels of methyl hypobromite ðCH3 OBrÞ. Optimized geometries, vibrational
frequencies, and relative energies have been obtained for the various stationary points. The O–Br bond scission to
CH3 O þ Br products and the 1,2 elimination pathway leading to HCHO þ HBr appear to be the most important dissociation channels. Analogous paths from the isomeric BrCH2 OH are also examined. The calculations are compared with
the results for the other two similar systems, CH3 OF and CH3 OCl. Ó 2002 Elsevier Science B.V. All rights reserved.
1. Introduction
The species CH3 OX (X ¼ halogen atom), especially those with X ¼ Cl, Br were early recognized
to play a significant role in several of the processes
involved in stratospheric ozone depletion cycles [1–
15]. Thus, numerous studies have been devoted to
the theoretical and experimental investigation of
the properties of these compounds [16–29]. Also
several studies have been devoted to the examination of the potential energy surface for the decomposition and isomerization pathways of two of
the members of this series, CH3 OF [30,31] and
CH3 OCl [32–35] and the experimental investigation of the related association reactions CH3 O þ X
and CH3 þ OX, X ¼ F, Cl, Br [8–11,14,15,36,37].
*
Corresponding author. Fax: +30-5109-8798.
E-mail address: [email protected] (A.M. Kosmas).
Hence, to contribute to the completion of this
family, the decomposition and isomerization
pathways of CH3 OBr are investigated in the present work.
As in the case of the other two similar compounds, CH3 OF and CH3 OCl, there are six main
channels in the decomposition scheme of CH3 OBr:
CH3 OBr ! HCHO þ HBr
ð1Þ
CH3 OBr ! BrCH2 OH
ð2Þ
CH3 OBr ! cis–HCOBr þ H2
ð3Þ
CH3 OBr ! CH3 O þ Br
ð4Þ
CH3 OBr ! CH3 þ OBr
ð5Þ
CH3 OBr ! CH2 þ HOBr
ð6Þ
In addition, the following production pathways
of the isomeric bromomethanol are of interest, i.e.,
0301-0104/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 1 - 0 1 0 4 ( 0 2 ) 0 0 7 2 0 - 6
306
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
the four-center 1,2 HBr elimination, (7), the 1,2 HH
elimination, (8), and the isomerization to CH3 OBr,
(9)
BrCH2 OH ! HCHO þ HBr
ð7Þ
BrCH2 OH ! H2 þ BrCHO
ð8Þ
BrCH2 OH ! CH3 OBr
ð9Þ
These processes are also examined as being closely
associated with the corresponding pathways of
CH3 OBr system.
2. Quantum mechanical calculations and results
The geometries of all reactants, products, and
stationary points have been fully optimized at the
UMP2(full)/6-311+G(d, p) level of theory. Harmonic frequency calculations were carried out at
the same level of theory and the zero-point energies
were determined. To improve the reliability of the
energetics, single-point energies at the QCISD(T)/
6-311+G(d, p) and UMP2(full)/6-311+G(3df, 2p)
levels of theory were calculated at the optimized
geometries. Based on these values G2MP2 theory
[38] was employed and the G2MP2 energies were
obtained. All calculations were performed with the
Gaussian 98 series of programs [39].
Optimized geometries for the stationary points
on the potential energy surface and BrCHO
product are shown in Fig. 1 and the reaction energy profile is depicted in Fig. 2. Like the other
members of the CH3 OX family, CH3 OBr possesses
a trans-structure in Cs symmetry in consistency
with the literature results and a cis-conformation
located 2.8 kcal mol1 higher. The second energy
minimum, BrCH2 OH, is located 34.5 kcal mol1
lower than CH3 OBr. Calculated harmonic vibrational frequencies and moments of inertia are listed in Table 1. Our geometrical and frequency
results for CH3 OBr are within 5% of the B3LYP/
6-311++G(3d2f, 3pd) results of Guha and Francisco [21,29] and the results of Messer et al. [22]
and Espinosa-Garcia [22,26]. In addition to the
energy minima five tight transition state structures
have been determined, labeled according to the
associated pathway as TS1, TS2, TS3, TS7, and
TS8. The stable structures are characterized by
positive frequencies and the transition states possess one imaginary frequency. The MP2/6311+G(d, p) and G2MP2 total electronic energies
and the relative energetics with respect to CH3 OBr
minimum for all decomposition channels studied,
(1)–(9), along with the corresponding ZPE corrections, are listed in Table 2. The structural and
frequency results obtained for H2 ; CH2 ; CH3 ;
CH3 O, and HCHO are in good agreement with
previous studies of other CH3 OX systems [30–33]
and they are not depicted here for space reasons.
Also the results for HBr and HOBr are in good
agreement with literature results [22,23,26,40].
As in both CH3 OF and CH3 OCl, an important
decomposition channel in CH3 OBr is the 1,2 hydrogen halide elimination process to HCHOþ
HBr products, channel (1). The mechanism involves first the isomerization to the cis-form
through a rotation about the C–O bond and the
subsequent elimination of HBr via a four-member
ring-type, tight transition state, TS1, located about
49 kcal mol1 . TS1 has Cs symmetry with an
imaginary frequency 3253i cm1 . The O–Br and
,
C–H bonds are elongated by 0.672 and 0.128 A
respectively, and the forming H–Br bond is 0.991
longer than the equilibrium bond length in HBr
A
molecule [40]. CH3 OBr is unstable with respect to
products HBr þ HCHO by 26 kcal mol1 . Channel (2) involves the isomerization to bromomethanol via the tight transition state, TS2, located
about 67 kcal mol1 higher with an imaginary
frequency 808i cm1 . The mechanism involves the
simultaneous migration of H atom to O and of Br
atom to C. The high isomerization barrier makes
CH3 OBr kinetically stable with respect to
BrCH2 OH but the isomeric bromomethanol is
thermodynamically more stable than methyl hypobromite by about 34 kcal mol1 . The third
channel (3) is a 1,1 HH elimination process leading
to H2 þ cis-HCOBr through the transition state
TS3, located at 71 kcal mol1 with an imaginary
frequency 1410i. The two breaking C–H bonds are
, respectively, and the forming
1.281 and 1.492 A
, i.e., only 0.367 A
H–H bond length is 1.105 A
longer than the equilibrium bond length in H2 .
The high transition state barrier in combination
with the considerable endothermicity, 32 kcal
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
307
Fig. 1. Optimized UMP2(full)/6-311+G(d, p) structures for stationary points on the potential energy surface. Distances are in
ngstr€
A
om and angles in degrees.
mol1 , makes this channel highly improbable at
thermal energies. Pathways (7) and (8) represent
similar decomposition channels of bromomethanol, quite analogous to (2) and (3) of CH3 OBr.
Thus, channel (7) is also a 1,2 elimination process
to HCHO þ HBr through the ring-type transition
state TS7 and channel (8) a 1,2 HH elimination to
H2 þ BrCHO through TS8. In TS8 the C–H and
308
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
Fig. 2. Potential energy surface for CH3 OBr and BrCH2 OH decomposition.
,
O–H bonds are elongated to 1.341 and 1.388 A
respectively.
The other three decomposition channels (4)–(6)
represent barrierless dissociation processes and no
detectable energy barriers could be determined,
like the similar processes in CH3 OF and CH3 OCl
systems. Channels (4) and (5) involve simple bond
fissions of O–Br and C–O bonds, respectively,
and channel (6) occurs through an H-shift
mechanism producing 1 CH2 and HOBr. The calculated potential energy surface shows that methyl hypobromite is very stable with respect to
the products of these three channels at thermal
reaction energies. As already said, these pathways
take place without tight transition state configurations and they represent cases of unimolecular
dissociations for which the reverse association
reactions are also barrierless. Such cases have
been an extensively treated subject and various
variational approaches have been suggested
within the frame of RRKM theory to handle the
absence of a well-defined critical configuration in
the initial addition step [41–45]. In the present
work we have adopted the variational procedure
of Schatz and coworkers [46]. Following this
approach, we have examined energies, geometries,
and frequencies at several reaction points RPij ,
i ¼ 4, 5, and 6, j ¼ a; . . . ; f , along the minimum
energy path for each of routes (4)–(6) by
increasing the relevant bond coordinate [47]. The
highest energy points in each pathway, labeled
RP4, RP5, and RP6 respectively, have been the
points where the minimization of the microcanonical rate constant has been achieved as we
shall see in the following section. In other words,
these points have been used, each, as a loose
critical point configuration for the pathway under
consideration. Their properties are also collected
in Table 1.
Of interest is the comparison of the potential
energy surface of the present system with CH3 OF
[30,31] and CH3 OCl [32–35], with which significant similarities and differences are observed.
Thus, as in CH3 OF and CH3 OCl; CH3 OBr is
thermodynamically stable with respect to all decomposition channels with the exceptions of the
1,2 hydrogen halide elimination, channel (1) and
the isomerization channel to the corresponding
halogenated methanol, channel (2). However, the
associated energy barriers for processes (1)–(4) are
located lower in CH3 OF [30,31] than in the other
two methyl hypohalites. Hence, larger values of
the microcanonical rate coefficients have been indeed obtained in CH3 OF [31] than in the other two
systems.
Among the important dissociation pathways of
bromethanol, the 1,2 elimination to HCHO þ HBr
appears to be the major channel followed by the
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
309
Table 1
2 ) for reactants, products, and stationary
UMP2(full)/6-31++-G(d, p) harmonic frequencies ðcm1 Þ and moments of inertia (amu A
points
Frequencies
CH3 OBra
cis-CH3 OBr
BrCH2 OH
TS1
TS2
TS3
TS7
TS8
RP4
RP5
RP6
CH3
CH2
cis-HCOBr
BrCHO
HOBr
OBr
HBr
CH3 O
HCHO
H2
3186,
3100,
3226,
3878,
3078,
3996,
3211,
3336,
3120,
3087,
3359,
3174,
3370,
3439,
3075,
3106,
3828,
750
2742
3140,
3052,
4533
CH3 OBr
BrCH2 OH
TS1
TS2
TS3
TS7
TS8
RP4
RP5
RP6
Ia
12.59
13.12
16.18
9.43
12.37
15.89
12.23
14.23
23.20
21.30
3156,
3083,
3203,
3235,
2988,
3241,
2688,
3187,
2360,
3086,
3358,
3079,
3370,
3206,
2068,
1799,
1143,
3067,
3012,
3108,
3133,
1680,
3127,
1746,
2740,
2059,
3049,
3166,
2983,
3177,
1145
1028,
1345,
681
1524,
1506,
1557,
1517,
1539,
1536,
1517,
1613,
1593,
1535,
1457,
1490,
1444,
1484,
1463,
1546,
1410,
1275,
1271,
1301,
1428,
1355,
1426,
1455,
1348,
1444,
1481, 1200, 1187, 1048, 581, 319, 253
1456, 1187, 1170, 1009, 592, 316, 234
1513, 1210, 1167, 1040, 592, 353, 258i
1355, 1196, 1126, 940, 625, 426, 306
1246, 1213, 970, 524, 356, 245, 3253i
1207, 1012, 950, 417, 415, 237, 808i
1087, 929, 847, 382, 315, 209, 1410i
1460, 1182, 1031, 894, 510, 250, 642i
1280, 1051, 885, 617, 551, 272, 2259i
1390, 1176, 1150, 1011, 213, 200, 200i
968, 687, 569, 540, 191, 68, 265i
895, 632, 475, 375, 250, 125, 153i
461
705, 348, 206
929, 663, 370
3103, 3020, 1545, 1430, 1423, 1136, 984, 809
2981, 1764, 1559, 1279, 1206
Ib
120.50
133.48
156.13
179.76
165.78
162.88
144.10
206.10
160.51
148.69
Ic
134.20
142.22
168.79
185.70
172.42
176.29
150.79
217.25
180.90
167.93
Ir
8.4
8.9
9.2
9.5
9.3
9.3
9.2
10.2
9.4
9.3
a
The first line contains the results of present work while the second line contains the results of Ref. [28] at the B3LYP/6311++G(3d2f, 3pd).
1,2 HH elimination to H2 þ BrCHO. The isomerization process is much less probable since the
associated isomerization transition state, TS2, is
located much higher in the potential energy surface compared to TS7 and TS8 for the elimination
processes. Two other fragmentation routes are
possible in principle as in chloromethanol [35], the
C–O and C–Br bond fission pathways, but the
products are very high located and they may become significant only at very large reaction energies under photogragmantation conditions as in
the ClCH2 OH case.
3. Unimolecular decomposition rate constants
The energy-specific microcanonical rate constants, ki ðJ ; EÞ, for the reaction channels (1)–(9)
were evaluated using the RRKM (Rice–Ramsperger–Kassel–Marcus) theory. For a given reaction step at an initial reactant energy E, ki ðJ ; EÞ
is given by
ki ðJ ; EÞ ¼ Wi ðJ ; EÞ=h.M ðJ ; EÞ;
ð10Þ
where J is the reactant rotational state, h is the
Planck’ s constant, .M ðJ ; EÞ is the density of states
310
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
Table 2
Total (Hartree) and relative (kcal mol1 ) energies and ZPE corrections ðkcal mol1 Þ for optimized species involved in CH3 OBr and
BrCH2 OH decomposition channels
Species
Total energies including ZPEa
CH3 OBr
BrCH2 OH
TS1
TS2
TS3
TS7
TS8
HCHO þ HBr
cis-HCOBr þ H2
CH3 O þ Br
CH3 þ OBr
CH2 þ HOBr
BrCHO þ H2
)2687.679082
)2687.743011
)2687.592982
)2687.618816
)2687.568812
)2687.680516
2687.602980
)2687.730792
)2687.626162
)2687.613421
)2687.543548
)2687.544343
)2687.726733
)2687.325622
)2687.386647
)2687.246238
)2687.216675
)2687.207924
)2687.326688
)2687.233295
)2687.368818
)2687.248742
)2687.267483
)2687.198105
)2687.181029
)2687.357843
)2687.461075
)2687.516156
)2687.382534
)2687.353863
)2687.347751
)2687.457151
)2687.376669
)2687.502526
)2687.388554
)2687.386790
)2687.335309
)2687.317277
)2687.497782
DEb
ZPE
0.0
)34.5
49.2
67.2
71.1
2.5
52.9
)26.0
45.4
46.6
78.8
90.2
)23.0
25.2
26.0
20.4
21.2
19.4
24.9
20.4
19.9
15.7
22.6
19.2
18.1
17.3
a
First column gives the optimized MP2/6-311+G(d, p) results, the second column the single point QCISD(T) results and the third
column the G2MP2 results. All electronic energies include the ZPE corrections.
b
Energy differences listed correspond to G2MP2 values. The reliability of these energy differences may be appreciated from the
comparison of the theoretical and experimental reaction enthalpies at 298 K for CH3 O þ Br ! HCHO þ HBr, which are )72.1 and
)65.7 [15] kcal mol1 , respectively.
available to the minimum, M ¼ CH3 OBr or
M ¼ BrCH2 OH, at a reactant energy E and
Wi ðJ ; EÞ is the number of states for the active degrees of freedom of the transition state TSi being
involved in the considered reaction step
i ¼ 1; . . . ; 9. The calculations have been carried out
employing the corresponding algorithm by Zhu
and Hase [48]. The required input for the calculations includes the relative energies, the vibrational harmonic frequencies, and the moments of
inertia, which are all collected in Tables 1 and 2.
RRKM theory was directly applied to the decomposition channels (1), (3), (7) and (8) and the
interisomerization processes (2) and (9), which
were found to proceed via the tight transition state
configurations, TS1, TS3, TS7, TS8, and TS2.
Processes (4)–(6) take place via barrierless decomposition pathways and for the examination of
these channels the principles of variational RRKM
theory were employed as described in the previous
section. According to variational theory, the bottleneck of a reaction occurs at the point along the
minimum energy path where the number of states
available, and hence the microcanonical rate constant, is at a minimum [41–47]. Consequently,
calculations have been done at several reaction
points along the minimum energy path for each
Fig. 3. Microcanonical rate constants kðJ ; EÞ for pathways (1)–
(6).
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
production pathway until a minimum in the rate is
found, thereby defining the reaction bottleneck.
Like in previous variational RRKM calculations
for radical-molecule and radical–radical barrierless association and decomposition reactions we
have found that the minimum in the rate occurs at
a reaction point, RPj , located at the highest energy
point along the minimum energy path [46,47].
These points labeled RP4, RP5, and RP6 have
been used for the evaluation of the microcanonical
rate coefficient for channels (4)–(6), respectively.
The calculations have been carried out in the
range of energies from E0 to 300 kcal mol1 and
J ¼ 50. The lowest energy value was set just equal
to the first dissociation potential threshold and the
selected J value was taken to be the highest populated rotational quantum number at 300 K. The
resulting microcanonical rate constants are shown
in Figs. 3 and 4 for CH3 OBr and BrCH2 OH decomposition, respectively. Due to the lowest dissociation threshold, k4 which corresponds to the O–
Br bond scission, assumes the greatest value of all
channels at the lowest energies but it is readily
followed by k1 the 1,2 HBr elimination. Thus, k1 ,
and k4 soon cross and k1 rises fast dominating the
overall dissociation process for a large energy range
up to 200 kcal mol1 . Above this value most
channels begin to compete and become important
with the exception of the O–Br bond scission,
channel (4) and the isomerization channel (2) that
fall lower. In the BrCH2 OH case things are more
Fig. 4. Microcanonical rate constants kðJ ; EÞ for pathways (7)–
(9).
311
clear and the resulting kðJ ; EÞ rise more slowly,
demonstrating the greater stability of bromomethanol. The most important decomposition
process remains the 1,2 elimination to HBrþ
HCHO throughout the interesting energy region.
The increasing contribution to the centrifugal
barrier with increasing J results in a considerable
drop of the microcanonical rate coefficient, kðJ ; EÞ
and hence a strong J dependence is obtained. To
demonstrate the effect of the J dependence, another series of calculations were carried out at two
additional J values, J ¼ 0 and 20, focused on
channels (1) and (4) that are the most interesting
production pathways of CH3 OBr decomposition.
The calculated k1 and k4 values are depicted in Fig.
5 which shows nicely the rapid drop of both rate
coefficients with increasing J and the faster decrease of k1 as the result of the tighter transition
state TS1 intervening in this process [49,50]. In
channel (4) where a loose transition state is accounted for, a weaker dependence is obtained
[49,50], since the large moments of inertia decrease
the rotational constants and weaken the J effect.
Detailed k values are also listed in Table 3 where
the same phenomena may be seen. Table 3 also
shows the decreasing significance of J as the energy
rises. Above 100 kcal mol1 the decrease in the k’s
with increasing J is much milder and the J effect is
much less dramatic in the high energy region.
A final comment may be made regarding the
energy ordering of the critical configurations for
the important decomposition channels, namely the
1,2 hydrogen halide elimination, the isomerization
to halogenated methanol and the oxygen–halogen
bond scission leading to methoxy radicals and
halogen atoms. This ordering may have an interesting influence on the reactions of methoxy radicals with X, X ¼ F, Cl, Br since the mechanism of
these reactions involves the intermediate formation of CH3 OX and its subsequent decomposition
following the potential energy surface studied.
Indeed, the various experimental studies [8,11,14,
15,36,37] have produced quite different values for
the bimolecular rate coefficient of each such reaction. A large rate constant, ð1:5 0:8Þ 1010
cm3 molecule1 s1 [36], almost unit probability in
every collision, was obtained in the CH3 O þ F !
HCHO þ HF reaction where the associated tran-
312
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
Fig. 5. Microcanonical rate constants kðJ ; EÞ for pathways (1) and (4) for different J values.
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
313
Table 3
Microcanonical rate coefficients, k1 and k4 in s1 for different J values
E (kcal mol1 )
50
52
54
56
58
60
62
64
68
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
102
104
106
108
k4
k1
J ¼0
20
50
J ¼0
20
50
5.65E8
5.34E9
2.38E10
7.57E10
1.95E11
4.38E11
8.82E11
1.64E12
2.85E12
7.43E12
1.13E13
1.67E13
2.39E13
3.33E13
4.55E13
6.09E13
8.01E13
1.04E14
1.32E14
1.67E14
2.08E14
2.56E14
3.12E14
3.76E14
4.51E14
5.35E14
6.31E14
7.39E14
8.61E14
2.52E8
3.56E9
1.78E10
6.02E10
1.62E11
3.73E11
7.68E11
1.45E12
2.56E12
6.81E12
1.04E13
1.55E13
2.23E13
3.14E13
4.30E13
5.79E13
7.64E13
9.92E13
1.27E14
1.61E14
2.00E14
2.47E14
3.02E14
3.65E14
4.38E14
5.21E14
6.16E14
7.22E14
8.42E14
2.63E6
5.06E8
4.35E9
1.97E10
6.44E10
1.71E11
3.90E11
8.01E11
1.51E12
4.44E12
7.08E12
1.09E13
1.61E13
2.33E13
3.27E13
4.48E13
6.03E13
7.96E13
1.03E14
1.32E14
1.67E14
2.09E14
2.58E14
3.15E14
3.81E14
4.57E14
5.43E14
6.42E14
7.52E14
7.75E9
2.66E10
7.08E10
1.60E11
3.21E11
5.91E11
1.02E12
1.66E12
2.57E12
5.58E12
7.87E12
1.08E13
1.46E13
1.93E13
2.50E13
3.19E13
4.02E13
5.00E13
6.15E13
7.49E13
9.02E13
1.08E14
1.28E14
1.50E14
1.75E14
2.03E14
2.34E14
2.69E14
3.06E14
5.37E9
2.02E10
5.67E10
1.33E11
2.74E11
5.14E11
8.99E11
1.48E12
2.33E12
5.14E12
7.29E12
1.01E13
1.37E13
1.81E13
2.36E13
3.03E13
3.83E13
4.78E13
5.89E13
7.19E13
8.68E13
1.04E14
1.23E14
1.45E14
1.70E14
L97E14
2.28E14
2.62E14
2.99E14
1.04E9
5.74E9
2.02E10
5.55E11
1.29E11
2.66E11
5.00E11
8.76E11
1.45E12
3.46E12
5.06E12
7.19E12
9.98E12
1.35E13
1.80E13
2.35E13
3.02E13
3.82E13
4.77E13
5.89E13
7.20E13
8.70E14
1.04E14
1.24E14
1.46E14
1.71E14
1.99E14
2.30E14
2.64E14
sition state barrier TS1 in the exit pathway is located about 9 kcal mol1 below the reactant energy
level, CH3 O þ F [30,31]. On the other hand, in
CH3 OCl and CH3 OBr systems, the quantum mechanically calculated transition states TS1 for the
similar decomposition pathways to HCHO þ HCl
and HCHO þ HBr, respectively, are calculated to
be around 2.5 kcal mol1 higher than the
CH3 O þ Cl [32–35] or CH3 O þ Br reactants. The
calculated small energy differences cannot claim to
be of chemical accuracy but they are in fair consistency with the varying but lower in general,
experimental rate constants measured [11,14,37] in
the Cl and Br cases. To summarize, we believe that
the present work contributes to the understanding
of the dissociation pathways of halogen hypohalides but we feel that the description of these sys-
tems is yet incomplete and more work is needed
for their full elucidation.
4. Summary
The potential energy surface for the important
decomposition channels of isomeric CH3 OBr and
BrCH2 OH molecules is investigated at the G2MP2
level of theory. Both isomeric species appear kinetically stable at thermal reaction energies. Microcanonical rate constant, kðJ ; EÞ, calculations
based on the constructed surface and RRKM
theory indicate that the most important decomposition channels at the lower energy region are
the O–Br bond scission to CH3 O þ Br and the 1,2
HBr elimination process to HCHO þ HBr. A
314
D.K. Papayannis et al. / Chemical Physics 282 (2002) 305–314
similar 1,2 HBr elimination process is shown to be
the most important decomposition channel in the
case of bromomethanol.
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