Shock tube determination of the overall rate of NH2 + NO → products in the thermal De-NOx temperature window

Article abstract of DOI:10.1002/kin.1068

The rate coefficient of the reaction NH₂ + NO → products (R1) was determined in shock tube experiments using frequency-modulation absorption spectroscopy for detection of NH₂. Because of the sensitivity of the diagnostic system, very low reactant concentrations could be employed in order to reduce the influence of secondary reactions on the NH₂ profiles. Benzylamine, C₆H₅CH₂NH₂, was used as a thermal source of the NH₂ radicals in the experiments. To determine the reaction rate, a perturbation strategy was employed that is based on changes in the NH₂ profiles when NO is added to the C₆H₅CH₂NH₂/Ar mixtures. The measured NH₂ profiles were interpreted by detailed kinetic modeling to obtain the overall reaction rate of R1 in the temperature range 1262-1726 K. The lower temperature limit of the present study is in the middle of the Thermal De-NOx temperature window. The present rate measurements are consistent with both our previous determination of the rate at higher temperatures and lower temperature data. A rate expression obtained by combining our higher temperature data and lower temperature data is. k₁ = 6.83 × 10¹⁵ T^-1.203 e^106/T(K) cm³ mol^-1 s^-1 for the temperature range 200-2500 K. The estimated uncertainty of the rate coefficient is ±20%.

Full text of DOI:10.1002/kin.1068

Shock Tube Determination
of the Overall Rate of
NH + NO → Products in
2
the Thermal De-NOx
Temperature Window
S. SONG, R. K. HANSON, C. T. BOWMAN, D. M. GOLDEN
Department of Mechanical Engineering, Stanford University, Stanford, California 94305
Received 7 June 2001; accepted 20 June 2001
ABSTRACT: The rate coefficient of the reaction NH + NO → products (R1) was determined
2
in shock tube experiments using frequency-modulation absorption spectroscopy for detection
of NH . Because of the sensitivity of the diagnostic system, very low reactant concentrations
2
could be employed in order to reduce the influence of secondary reactions on the NH profiles.
2
Benzylamine, C H CH NH , was used as a thermal source of the NH radicals in the experi-
6
5
2
2
2
ments. To determine the reaction rate, a perturbation strategy was employed that is based on
changes in the NH profiles when NO is added to the C H CH NH /Ar mixtures. The measured
2
6
5
2
2
NH profiles were interpreted by detailed kinetic modeling to obtain the overall reaction rate of
2
R1 in the temperature range 1262–1726 K. The lower temperature limit of the present study is
in the middle of the Thermal De-NOx temperature window. The present rate measurements are
consistent with both our previous determination of the rate at higher temperatures and lower
temperature data. A rate expression obtained by combining our higher temperature data and
lower temperature data is
1
5
� 1.203
e106/T (K) cm mol
s
� 1 � 1
3
k = 6.83 � 10
T
1
for the temperature range 200–2500 K. The estimated uncertainty of the rate coefficient
is � 20%. �C 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 715–721, 2001
INTRODUCTION
combustion systems. In these processes, the reaction
of NH2 with NO plays an important role, and this re-
action has two major product channels [1,2]. One is a
chain branching channel
TheThermalDe-NOxandreburningprocessesareused
to reduce nitrogen oxide emissions from stationary
NH2 + NO → NNH + OH
and the other is a chain terminating channel
NH2 + NO → N2 + H2O
(R1a)
We wish Simon Bauer the happiest 90th birthday, and we salute
his long list of contributions to science.
Correspondence to: S. Song; e-mail: shsong@stanford.edu.
Contract grant sponsor: U.S. Department of Energy, Office of
Basic Energy Sciences, Division of Chemical Sciences.
�
c 2001 John Wiley & Sons, Inc.
(R1b)

7
16
SONG ET AL.
Two important kinetic parameters in modeling the
C6H5CH2NH2/Ar mixture and experiments were per-
formed at nearly identical conditions as those for the
C6H5CH2NH2 pyrolysis experiments. In this case, the,
NH2 profile is perturbed by the added NO, and the de-
cay rate of NH2 increases significantly because of the
reaction of NH2 with NO (see Fig. 1).
Thermal De-NOx process are the overall rate coeffi-
cient of the NH2 + NO reaction, k1 = k1a + k1b, and
the branching ratio, � = k1a/k1. As a result of many
experimental and theoretical studies, a consensus ex-
ists for the branching ratio, �, in the temperature range
3
00–2000 K [3,4]. As for the overall rate coefficient,
To determine k1 values, the perturbed NH2
profiles were interpreted using a detailed 63-reaction
mechanism that was optimized by analyzing the
C6H5CH2NH2 pyrolysis data (see Table I). This re-
action mechanism comprises relevant reactions from
Thermal De-NOx chemistry [4,16] and toluene,
benzyl [12,13], and cyclopentadiene [14] pyrolysis
mechanisms.
In the first step of the perturbation method, we
performed NH2-sensitivity analysis [17] and chose
the key reactions whose rate coefficients were ad-
justed to optimize the base mechanism for benzylamine
pyrolysis. A result of NH2-sensitivity analysis for a
C6H5CH2NH2/Ar experiment is shown in Fig. 2. At
this experimental condition, the C6H5CH2NH2 decom-
position (R2) is important for NH2 production, and the
NH2 decay is sensitive to R8, R28, and R30. At lower
temperatures, the reaction between C6H5CH2NH2 and
NH2 (R5) is important. As temperature increases, the
NH2 becomes more sensitive to reactions between frag-
ments of the benzyl radical, C6H5CH2, and the NH2
radical because C6H5CH2 starts to decompose at high
temperature. We assumed that C5H5, C4H4, C3H3,
and C2H2 were fragments of C6H5CH2 and included
k1, the low temperature studies show consistent results,
but two issues remain for temperatures above 1400 K.
The first issue is uncertainty in the absolute value of k1
at high temperatures, where there are significant dis-
crepancies among the experimental studies. The sec-
ond is the temperature dependence of this rate coef-
ficient. Deppe et al. [5] and Roose et al. [6] reported
a positive temperature dependence, while Miller and
Klippenstein reported a negative temperature depen-
dence in their theoretical study [7]. Recently, Song and
coworkers measured k1 with small uncertainty in the
temperature range 1716–2507 K and observed no ev-
idence of a positive temperature dependence for this
reaction [8]. However, there still is a need for data at
temperatures below 1400 K because the Thermal De-
NOx process is very sensitive to this reaction rate coef-
ficient and the branching ratio in the Thermal De-NOx
temperature window (1100–1400 K). The objective of
the present study is to measure k1 values in the Thermal
De-NOx window.
METHOD OF APPROACH
We have employed a frequency-modulation (FM) ab-
sorption technique [9–11] for the sensitive detection of
NH2 radicals in shock tube experiments. In our previ-
ous study, monomethylamine (CH3NH2) was used as
a source of the NH2 radical [8]. However, CH3NH2
is not suitable for low temperature experiments since
the decomposition rate of CH3NH2 below 1700 K is
too slow to produce sufficient NH2 radicals for our ex-
perimental conditions. In the present study, we used
benzylamine (C6H5CH2NH2) that decomposes rapidly
at lower temperatures to produce NH2 radical.
A perturbation method was applied to reduce the
uncertainty resulting from the influence of secondary
reactions. First, a set of pyrolysis experiments of
C6H5CH2NH2 in Ar was performed behind reflected
shock waves, and the NH2 mole fraction was measured
as a function of time. Initially, C6H5CH2NH2 rapidly
decomposes to produce NH2 and C6H5CH2 via
Figure 1 Example NH2 mole fraction profiles: (a) 30 ppm
C6H5CH2NH2/0%NO/Ar balance, T = 1488 K, P = 1.37
bar; (b) 30 ppm C6H5CH2NH2/900 ppm NO/Ar balance,
T = 1491 K, P = 1.39 bar. Solid lines are best fits to the
data using a detailed kinetic model (Table I). Broken lines
are � 10% variation in k1.
C6H5CH2NH2 → C6H5CH2 + NH2
(R2)
After reaching a maximum value, the NH2 slowly
decays, reacting with itself and other products of the
decomposition process. Next, NO was added to the

SHOCK TUBE DETERMINATION OF THE OVERALL RATE OF NH + NO → PRODUCTS
717
2
Table I Reaction Mechanism Used for Data Analysis
Reaction
A
n
Ea
Ref.
R1a
R1b
R2
R3
R4
R5
R6
R7
R8
NH2 + NO → NNH + OH
4.29E10
2.61E19
5.49E14
5.00E13
1.00E13
4.00E12
1.00E12
1.00E13
2.00E14
5.00E12
2.51E16
1.26E16
2.00E13
3.90E11
2.90E11
1.40E11
3.00E11
3.70E12
2.00E11
1.00E13
1.00E13
2.00E11
2.00E14
3.02E14
5.00E12
1.50E13
1.50E13
5.00E12
5.00E13
5.00E13
5.48E14
2.00E11
1.50E13
4.00E06
2.20E16
6.40E05
9.40E06
2.00E06
3.00E11
1.30E13
8.50E13
4.00E13
3.90E12
3.50E16
1.60E12
5.00E12
1.00E13
1.00E13
1.00E12
2.00E13
5.00E16
5.00E13
1.00E13
2.00E13
0.294
� 2.369
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
1.00
1.00
1.00
1.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
2.00
0.00
2.39
1.94
2.04
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
� 3639
3624
275300
33500
20900
0
12600
21000
0
1930
407522
405848
16711
322599
321771
123884
140599
47400
251000
334700
305400
213400
60700
60700
0
See text
See text
See text
est.
est.
est.
est.
est.
[12]
[12]
[13]
[13]
[14]
[14]
[14]
[14]
[14]
[15]
[12]
[12]
[12]
12]
[12]
[12]
est.
est.
NH2 + NO → N2 + H2O
C6H5CH2NH2 ↔ C6H5CH2 + NH2
C6H5CH2NH2 + H → C6H5CHNH2 + H2
C6H5CH2NH2 + NH → C6H5CHNH2 + NH2
C6H5CH2NH2 + NH2 → C6H5CHNH2 + NH3
C6H5CH2 + NH2 → C6H5CH + NH3
C6H5CH2 + NH → C6H5CH + NH2
C6H5CH2 + H → C6H5CH3
2C6H5CH2 ↔ C6H5CH2CH2C6H5
C6H5CH2 → C5H5 + C2H2
C6H5CH2 → C4H4 + C3H3
C5H5 + C5H5 → C10H8 + 2H
C5H5 → C5H5-3
R9
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24
R25
R26
R27
R28
R29
R30
R31
R32
R33
R34
R35
R36
R37
R38
R39
R40
R41
R42
R43
R44
R45
R46
R47
R48
R49
R50
R51
R52
R53
C5H5 → C5H5-3b
C5H5-3 → C2H2 + C3H3
C5H5-3b → C2H2 + C3H3
C2H2 + NH2 → HCN + CH3
C4H4 → C4H3 + H
C4H4 → 2C2H2
C4H4 → C4H2 + H2
C4H3 → C4H2 + H
C4H3 + H → C4H2 + H2
C4H4 + H → C4H3 + H2
C5H5 + NH2 → C5H6 + NH
C3H3 + NH2 → C3H2 + NH3
C3H3 + NH2 → C3H4 + NH
C4H4 + NH2 → C4H5 + NH
NH2 + H ↔ NH + H2
0
0
0
est.
est.
15272
0
79200
0
See text
[16]
See text
See text
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
NH2 + NH ↔ N2H2 + H
NH2 + NH2 ↔ NH3 + NH
NH2 + NH2 ↔ N2H2 + H2
NH2 + NH2 (+M) ↔ N2H4 (+M)
NH2 + OH ↔ NH + H2O
NH3 + M ↔ NH2 + H + M
NH3 + H ↔ NH2 + H2
0
4184
391078
42555
27029
2368
92048
10460
5021
0
6276
192464
0
20920
0
4184
62760
0
209200
4184
4184
4184
NH3 + O ↔ NH2 + OH
NH3 + OH ↔ NH2 + H2O
NH3 + HO2 ↔ NH2 + H2O2
N2H4 + H ↔ N2H3 + H2
N2H4 + O ↔ N2H2 + H2O
N2H4 + OH ↔ N2H3 + H2O
N2H4 + NH2 ↔ N2H3 + NH3
N2H3 + M ↔ N2H2 + H + M
N2H3 + H ↔ NH2 + NH2
N2H3 + O ↔ N2H2 + OH
N2H3 + O ↔ NH2 + HNO
N2H3 + OH ↔ N2H2 + H2O
N2H3 + OH ↔ NH3 + HNO
N2H3 + NH ↔ N2H2 + NH2
N2H2 + M ↔ NNH + H + M
N2H2 + H ↔ NNH + H2
N2H2 + O ↔ NH2 + NO
N2H2 + O ↔ NNH + OH
[16]
Continued

7
18
SONG ET AL.
Table I Continued
Reaction
A
n
Ea
Ref.
R54
R55
R56
R57
R58
R59
R60
R61
R62
N2H2 + OH ↔ NNH + H2O
N2H2 + NO ↔ N2O + NH2
N2H2 + NH ↔ NNH + NH2
N2H2 + NH2 ↔ NNH + NH3
NNH ↔ N2 + H
1.00E13
3.00E12
1.00E13
1.00E13
6.70E07
1.00E14
5.00E13
5.00E13
5.00E13
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
4184
[16]
[16]
[16]
[16]
[4]
[16]
[16]
[16]
[16]
0
4184
4184
0
0
0
0
0
NNH + H ↔ N2 + H2
NNH + OH ↔ N2 + H2O
NNH + NH ↔ N2 + NH2
NNH + NH2 ↔ N2 + NH3
n
3
The rate constant are given by k = AT exp(� E
a
/RT ) in cm , mol, s, J units.
reactions between these radicals and NH2 in the reac-
tion mechanism.
decomposition reaction will be reported separately.
As for rate coefficients of R28 and R31, the litera-
ture values [16] were slightly modified for the purpose
of optimization of the reaction mechanism. The ini-
tial value of the reaction rate of R30 was taken from
our previous study [8] and adjusted slightly during the
optimization procedure for C6H5CH2NH2 pyrolysis
experiments. Most of the other reaction rates were
taken from literature. However, some of reaction rates
that were not available in the literature were estimated.
As mentioned previously, our goal was to determine
k1 values, and the reaction mechanism was optimized
to predict NH2 profiles during C6H5CH2NH2 pyroly-
sis under specific experimental conditions. Therefore,
the reaction mechanism reported in Table I should be
used only for the range of conditions of the present
study.
C6H5CH2NH2 → NH2 → C6H5CH2NH + NH3
(R5)
C6H5CH2 + H → C6H5CH3
NH2 + H → NH + H2
(R8)
(R28)
(R30)
NH2 + NH2 → NH3 + NH
The rate coefficient of the C6H5CH2NH2 decompo-
sition reaction (R2) was determined using the initial
slope of the measured NH2 trace. According to the
RRKM calculations, R2 is in the fall-off region for
the experimental conditions of the present study, so the
rate expression of R2 in Table I is valid only for
temperature range 1250–1750 K and pressure range
Figure 3 shows a NH2 sensitivity plot for a
C6H5CH2NH2/NO/Ar experiment. The most important
1.1–1.4 bar. The results of our study of C6H5CH2NH2
Figure 2 Results from NH2 sensitivity analyses for the con-
ditions of Fig. 1a: 30 ppm C6H5CH2NH2/0%NO/Ar balance,
T = 1488 K, P = 1.37 bar.
Figure 3 Results from NH2 sensitivity analyses for the con-
ditions of Fig. 1b: 30 ppm C6H5CH2NH2/900 ppm NO/Ar
balance, T = 1491 K, P = 1.39 bar.

SHOCK TUBE DETERMINATION OF THE OVERALL RATE OF NH + NO → PRODUCTS
719
2
reaction isthe NH2 + NO reaction. While the NH2 trace
is sensitive to the C6H5CH2NH2 decomposition reac-
tion (R2) during the very early stage of reaction, this
reaction has a very small effect on the k1 determination
because R1 and R2 are decoupled in terms of time. In
addition, the sensitivity to the branching ratio is small
compared with R1. Therefore, any uncertainty in the
branching ratio does not have a significant effect on
the k1 determination.
C6H5CH2NH2 can be decreased to reduce the influence
of secondary reactions.
RESULTS AND DISCUSSION
Experiments were conducted in the temperature range
1
262–1726 K. The pressure was between 1.14 and 1.45
bar. In total, 44 NH2 traces from C6H5CH2NH2 and NO
experiments were analyzed. The initial concentration
of benzylamine was varied from 20 to 40 ppm, and
the ratio of NO to C6H5CH2NH2 from 11 to 60. As
shown in Fig. 4, no systematic effect on the k1 deter-
mination was observed when different initial concen-
trations of NO in the mixture or different ratios of NO
to C6H5CH2NH2 were used. Consequently, the results
of our experiments are independent of the initial con-
centration of NO and the ratio of NO to C6H5CH2NH2
in the initial gas mixture. In addition, the results of
C6H5CH2NH2 experiments are consistent with those
of our previous study using CH3NH2 [8]. The vertical
error bars in Fig. 4 indicate the combined uncertainties,
which include fitting errors, influence of uncertainties
of other reaction rate parameters, and uncertainties in
the NH2 absorption coefficient at the wavelength of
interest. The combined uncertainties depend on tem-
perature and vary from � 12% (at 1432 K) to � 17%
EXPERIMENTAL
Experiments were performed behind reflected shock
waves in a stainless steel shock tube (15.4 cm inside
diameter, 10.5 m long driven section, and 3.7 m long
driver section). To reduce impurities and residue, the
shock tube was evacuated to an ultimate pressure of
�
7
2
.5 � 10 torr using a turbomolecular pump before
eachexperiment, andthecombinedleakandoutgassing
�
6
� 1
rate was typically 4 � 10 torr min . The diagnostic
laser beam passes through the optical windows, which
are located at 2 cm apart from the endwall. Tempera-
ture and pressure behind the reflected shock wave were
calculated from the initial temperature and pressure,
and the shock speed measured over four intervals us-
ing five piezoelectric pressure gauges. The estimated
uncertaintyinreflectedshocktemperaturewaslessthan
(at 1726 K). The major source of uncertainty at low
�
20 K at 1400 K over the time intervals of interest.
Liquid C6H5CH2NH2 (>99.5%, Aldrich) was evap-
orated in a temperature-controlled bubble saturator,
from which a mixture of Ar (>99.9999%, Praxair) and
C6H5CH2NH2 vapor was continuously supplied to the
shock tube. The flow scheme used in the present study
reduces the uncertainty in the initial concentration of
C6H5CH2NH2 due to wall adsorption. To measure the
actual concentration of the C6H5CH2NH2 entering the
shock tube, absorption of C6H5CH2NH2 was measured
between the bubble saturator and the shock tube us-
ing a 3.39 ␮m He–Ne laser. A commercially available
NO/Ar mixture (1.98% of NO, Praxair) was used in
the perturbation experiments. The NO2 and N2O im-
purities in the NO/Ar mixture were measured using an
FTIR. The mole fractions of NO2 and N2O were 42 and
51 ppm, respectively. The influence of the NO2 and
N2O impurities on the k1 determination is negligible
for the conditions of the present study.
To measure the NH2 concentration, we used a FM
absorption technique. A detailed description of the
FM absorption setup used in the present study was
given by Vostsmeier et al. [18]. With FM absorption,
at least a factor of 10 reduction in the NH2 detection
limit can be achieved in comparison with direct laser
absorption. Consequently, the initial concentration of
Figure 4 Comparison of the results of C6H5CH2NH2 and
CH3NH2 experiments. Data from C6H5CH2NH2 experi-
ments: � 300 ppm NO;
�
500 ppm NO; N 600 ppm NO;
H 800 ppm NO; � 900 ppm NO; + 0.12% NO; � data from
CH3NH2 experiments [8]; - - - Eq. (1). The vertical bars rep-
resent the combined fitting errors and uncertainties associated
with secondary reactions and absorption coefficient.

7
20
SONG ET AL.
temperature (below 1350 K) is uncertainties in the re-
action rates of the secondary reactions including R2. At
mid and high temperatures (above 1350 K), the con-
tribution of the fitting error and the uncertainties in
chemistry to the total uncertainty is comparable. The
k1 values are tabulated in Table II together with the
experimental conditions.
Our C6H5CH2NH2 and CH3NH2 data are consistent
with the lower temperature data as shown in Fig. 5.
Combination of our high temperature data with lower
temperature data from the most recent flow reactor
experiments of Wolf et al. [25] results in the follow-
ing expression for k1 in the temperature range 200–
2500 K.
15
� 1.203
e106/T (K) cm mol
s (1)
� 1 � 1
3
k1 = 6.83 � 10
T
Table II Summary of k with Experimental Conditions
1
log10 k1
The uncertainty in the given rate coefficient is es-
timated to be � 20%. Compared with the theoretical
results of Miller and Klippenstein [7], the current k1
rate expression is yields values about 25% lower than
their k1 values in the Thermal De-NOx temperature
window.
In our previous study of the branching ratio, we
noted that the branching ratio determination depends
slightly on the overall rate of the NH2 + NO reac-
tion [3]. With the new values of k1 given by Eq. (1),
the earlier branching ratio data were reevaluated. As
seen in Fig. 6, the effect of k1 on the branching ratio
determination is very small, and the updated branch-
ing ratio shows even better agreement with branching
ratio from Miller and Klippenstein’s theoretical work
[7]. For modeling purposes, we suggest the following
rate expressions for R1a and R1b, which were calcu-
lated using their branching ratio results data [7] and the
3
� 1 � 1
s )
T (K) P (bar) xBA (ppm) xNO (ppm) (cm mol
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
262
266
267
278
281
283
298
299
304
305
320
326
349
351
352
355
358
359
367
390
422
427
428
432
447
473
488
491
507
530
548
550
565
565
580
590
607
616
661
669
681
682
703
726
1.24
1.28
1.27
1.26
1.26
1.28
1.29
1.25
1.24
1.34
1.27
1.24
1.41
1.32
1.14
1.29
1.28
1.32
1.32
1.45
1.26
1.42
1.44
1.41
1.33
1.30
1.39
1.40
1.41
1.43
1.24
1.28
1.35
1.30
1.24
1.28
1.33
1.28
1.32
1.30
1.34
1.27
1.24
1.29
40
40
40
41
40
42
28
40
35
26
22
26
28
41
29
31
31
30
29
27
27
27
27
29
26
30
30
30
24
24
20
19
26
21
19
19
26
20
20
19
21
20
21
20
530
530
530
530
530
530
320
530
530
880
880
900
880
530
320
900
900
900
900
890
320
900
610
610
880
320
880
880
880
880
810
810
880
810
810
810
880
1190
1190
810
1200
810
810
810
12.15
12.14
12.13
12.15
12.14
12.12
12.13
12.13
12.12
12.12
12.11
12.11
12.10
12.10
12.09
12.09
12.08
12.08
12.07
12.09
12.07
12.06
12.04
12.06
12.04
12.04
12.03
12.03
12.02
12.02
12.03
12.01
11.99
12.01
12.01
12.03
11.99
12.00
11.99
11.97
11.99
12.00
11.97
11.97
Figure 5 Summary of k1: � Data from C6H5CH2NH2 ex-
periments; � data from CH3NH2 experiments [8];
�
[19];
M [20]; O [21]; ♦ [22]; + [23]; � [24]; ✳ [25]; — [7]; - - -
Eq. (1). The vertical bars represent the combined fitting er-
rors and uncertainties associated with secondary reactions
and absorption coefficient.

SHOCK TUBE DETERMINATION OF THE OVERALL RATE OF NH + NO → PRODUCTS
721
2
BIBLIOGRAPHY
1
2
3
4
5
6
7
8
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3
. Miller, J. A.; Glarborg, P. Int J Chem Kinet 1999, 31,
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061–2069.
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Figure 6 Reevaluation of the branching ratio: � updated
branching ratio using Eq. (1); � [3]; — [7].
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0. Whittaker, E. A.; Wendt, H. R.; Hunziker, H. E.;
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1
1
1
1
1
overall rate coefficient given by Eq. (1).
k1a = 4.29 � 10 T 0.294 e438/T (K)cm mol
1
0
3
� 1 � 1
s
(2)
19
� 2.369 � 436/T (K)
3
� 1 � 1
k1b = 2.61 � 10
T
e
cm mol s
1
997, 101, 7105–7113.
(3)
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Proc Combust Inst 1998, 27, 329–336.
These rate expressions are valid for temperature range
00–1900 K. In this temperature range, the sum of k1a
and k1b slightly deviates from k1 in Eq. (1) by less than
%.
15. Hennig, G.; Wagner, H. Gg. Ber Bunsen-Ges Phys Chem
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4
1
1
1
1
6. Glarborg, P.; Dam-Johansen, K.; Miller, J. A. Int J Chem
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5
8
7-8248; Sandia National Laboratories, 1987.
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Int J Chem Kinet 1999, 31, 445–453.
9. Lesclaux, R.; Kh eˆ , P. V.; Dezauzier, P.; Soulignac, J. C.
Chem Phys Lett 1975, 493–497.
CONCLUSION
Frequency-modulation absorption spectroscopy and a
perturbation method were employed in shock tube ex-
periments to obtain an accurate determination of the
overall rate of the NH2 + NO reaction in the tempera-
ture range 1262–1726 K. Use of C6H5CH2NH2 as an
NH2 source allowed extension of the k1 determination
to the Thermal De-NOx temperature window. A new
expression for k1 is recommended which provides a
consistent fit to k1 data over the temperature range 200–
20. Silver, J. A.; Kolb, C. E. J Phys Chem 1982, 86, 3240–
246.
3
2
1. Stief, L. J.; Brost, W. D.; Nava, D. F.; Borkowski, R. P.;
Michael, J. V. J Chem Soc Faraday Trans 2 1982, 78,
1
391–1401.
2
2
2
2. Atakan, B.; Jacobs, A.; Wahl, M.; Weller, R.; Wolfrum,
J. Chem Phys Lett 1989, 155, 609–613.
3. Wolf, M.; Yang, D. L.; Durant, J. L. J Photochem Pho-
tobiol A: Chem 1994, 80, 85–93.
2500 K and updated rate expressions for two product
4. Park, J.; Lin, M. C. J Phys Chem 1997, 101, 5–13.
channels of the NH2 + NO reaction were obtained for
25. Wolf, M.; Yang, D. L.; Durant, J. L. J Phys Chem 1997,
101, 6243–6251.
the temperature range 400–1900 K.