Analysis of products from a C2H2/N2 microwave discharge: New nitrile species

Article abstract of DOI:10.1016/S0009-2614(99)00999-9

The production of gaseous hydrocarbons, nitriles, amines, and hydrazines in a continuous-flow microwave plasma discharge excited in a 20% C₂H₂+80% N₂ mixture at a pressure of 20 Torr is reported. The product analysis was made by Li⁺ ion attachment mass spectrometry. A variety of N-containing organics (identified as HC_nN (n=1-7), NC(CC)_nCN (n=0-2), NC(CH₂)_nCN (n=0-6), C_nH_2n-1NH₂ (n=0-6), C_nH_2n+1N(H)NH₂ (n=0-5), etc.) were formed and these were tentatively assigned to nitriles, amines, and hydrazines. The mass-spectral analysis exhibited progressions differing by 14 mass units. Reaction schemes were proposed to explain the formation of some molecules.

Full text of DOI:10.1016/S0009-2614(99)00999-9

19 November 1999
Ž
.
Chemical Physics Letters 313 1999 733–740
www.elsevier.nlrlocatercplett
Analysis of products from a C2 H2rN2 microwave discharge: new
nitrile species
)
Toshihiro Fujii
National Institute for EnÕironmental Studies, 16-2 Onogawa, Tsukuba Science City, Ibaraki 305-0053, Japan
Received 12 July 1999; in final form 31 August 1999
Abstract
The production of gaseous hydrocarbons, nitriles, amines, and hydrazines in a continuous-flow microwave plasma
discharge excited in a 20% C2H2q80% N2 mixture at a pressure of 20 Torr is reported. The product analysis was made by
Liq ion attachment mass spectrometry. A variety of N-containing organics identified as HCnN ns1–7 , NC C[C CN
Ž
Ž
.
Ž
.
n
Ž
.
Ž
.
Ž
.
Ž
.
Ž .
Ž
.
.
ns0–2 , NC CH2 nCN ns0–6 , CnH2 ny1NH2 ns0–6 , CnH2 nq1N H NH2 ns0–5 , etc. were formed and these
were tentatively assigned to nitriles, amines, and hydrazines. The mass-spectral analysis exhibited progressions differing by
14 mass units. Reaction schemes were proposed to explain the formation of some molecules. q 1999 Elsevier Science B.V.
All rights reserved.
Ž .
free radicals such as CnH3 ns2 and 4 , CnH5
1. Introduction
Ž
.
Ž
.
ns2, 4, and 6 , and CnH7 ns3 and 4 . In recent
Ž
.
A microwave MW discharge plasma is a prime
method for the production of various kinds of novel
compounds, since many products may be generated
in complex ways 1,2 . In the search for materials
with new physical properties, nitrogen compounds
are a reasonable target since the nitrogen atom forms
3, 4, or 5 covalent bonds leading to unique structural
characteristics.
studies related to C2 H2 MW plasma, Bondybey and
w
x
co-workers 9–11 identified a variety of conjugated
Ž
molecular products: cyanocarbon series CnN2 ns4,
w
x
.
w x
9
5
and cyanopolyacetylene radical cations
NC C[C CN
there would be considerable interest in seeking new
q
Ž
.
w
x
10,11 . These results suggested
n
products in a C2 H2rN2 MW discharge system.
The recently developed Liq ion attachment mass
q
w
x
Ž
.
Several workers 3–8 , including some astrophysi-
spectrometry Li MS provides mass spectra of
quasi-molecular ions formed by lithium ion attach-
w
x
cists 6,7 , have reported the presence of various
chemical groups produced by electrical discharges in
w
ment to chemical species under high pressure 12–
w x
x
C2 H2. For instance, Fujii 8 reported the unex-
pected formation of many unfamiliar neutral hydro-
14 . Results are obtained in the form of mass-spec-
trometric traces of Liq adducts. As an example
Ž
.
w
x
carbon HC products, among which were various
15,16 , the method was successfully applied to the
study of neutral species that emerge from CH4rO2
microwave discharge plasmas. It was demonstrated
that LiqMS provides only molecular ions and direct
)
Fax: q81-298-50-2574; e-mail: t-fujii@nies.go.jp
0009-2614r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
Ž
.
PII: S0009-2614 99 00999-9

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)
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T. FujiirChemical Physics Letters 313 1999 733–740
determination of unstable, intermediary and reactive
species is allowed.
sible to directly detect products, and is essentially
identical to that used in an earlier identification study
w x
In the present Letter, I report our mass-spectral
observations of products from a C2 H2rN2 plasma
and present analysis suggesting that they are nitriles,
amines, and hydrazines – compounds of potential
significance as new substances. I also report some
of unfamiliar products in a C2 H2 plasma 8 .
The MW source was constructed from a straight
Ž
quartz tube 3 mm inner diameter, 6 mm outer
.
diameter, 20 cm in length . The C2 H2 gas, premixed
with N2 , flows down this tube. The MW plasma was
created by connecting the cavity to a 2.465 MHz
MW generator through a matching network. All the
experiments were performed under the following
conditions: total pressure upstream at the flow tube,
20 Torr; total pressure at the Liq reactor, 0.2 Torr;
MW power, 30 W; total gas flow rate, 10 cm3rmin.
The species produced by the MW discharge ef-
fused via a flow tube into the Liq reactor. The
products were monitored by measuring the Liq-ad-
duct ion mass spectrum. Measurements were taken
135 mm away from the Liq emitter. Here the mass
signal intensities of the ionic species coming from
the plasma were confirmed to be negligible by con-
Ž
.
new series of nitrile neutrals, such as NC C[C CN
n
Ž
.
and NC CH2 nCN, which are of considerable inter-
est as potential interstellar or planetary species, as
well as being of both theoretical and synthetic impor-
tance. Finally, plausible reaction schemes to explain
their formation are considered.
2. Experimental
I
utilized
a
MW discharge sourcerLiq
reactorrquadrupole mass spectrometer, as described
previously 12–14 . This arrangement makes it pos-
w
x
Fig. 1. Typical mass spectra of Liq adducts showing the neutral products formed in the 20% C2 H2 q80% N2 A and 20% C2 H2 q80%
Ž .
Ž
.
Ar B MW discharge plasmas. The experimental conditions were the same in both plasmas. Only those peaks with intensity )3% of that
Ž .
Ž
.
Ž .
of the base peak, mrz 48, in the A spectrum are drawn. Note: the signal intensity scale of A is different from that of B .

(
)
T. FujiirChemical Physics Letters 313 1999 733–740
735
trol experiments using continuous flow C2 H2rN2
3. Results and discussion
mixtures of varied proportions but without Liq emis-
sion. This arrangement was found optimal for accu-
rate identification of the various neutral products. A
second control experiment was performed using a
continuous flow plasma discharge with Ar in place
of the N2. On the simple basis of the inertness of Ar,
different products might be expected.
3.1. Mass spectra
Typical Liq-adduct ion mass spectra of neutral
chemical species produced in N2 80% –C2 H2 20%
Ž
.
Ž
.
Table 1
Neutral productsa formed by a MW discharge in a mixture of 20% C2 H2 q80% N2 compared with those formed in a mixture of 20%
Ž
.
C2 H2 q80% Ar. Relative intensities in parentheses are given as a percentage relative to the mrzs48 peak from the N2rC2 H2 system.
All products of both N2rC2 H2 and ArrC2 H2 plasmas with a relative peak intensity of )3% are listed
mrza
N2rC2 H2
ArrC2 H2
mrza
N2rC2 H2
ArrC2 H2
Ž
.
Ž .
23
25
34
NH2 29
24
33
35
NH3 65
Ž .
Ž
.
Ž .
C2 H2 4
Ž .
C2 H4 3
H2O 32
C2 H2
6
Ž
.
Ž
.
HCN 43
C2 H3 12
Ž
.
.
Ž .
Ž
.
.
36
39
47
50
H2C5NH 11
C2 H5
5
38
46
48
51
CH3NH2 4.4
Ž
Ž
.
Ž
N2 H4 4.8
Ž .
CN H C 7.4
Ž .
Ž
.
Ž .
5
C3H4
6
C3H4
C3H7
3
CH3CN 100
CH3N5NH 21
C3H5
C4 H2
Ž
.
Ž .
6
Ž .
C2 H3NH2 15
Ž
.
Ž
.
52
56
C2 H5NH2 14
53
57
CH3N2 H3 5.0
Ž .
Ž
.
Ž .
4
C4H? 4.6
C4 H2
4
Ž
.
Ž
.
Ž .
Ž .
C2 HN5NH 6
C2 H3N5NH 8.9
58
60
62
HCCCN 51
C4 H3 12
59
61
63
NCCN 10
Ž
Ž
.
.
C2 H3CN 18
C2 H5CN 24
Ž
.
.
Ž
.
64
C3H5NH2 7.7
65
C2 H5N5NH Ž8.1
Ž
.
Ž
.
66
70
C3H7 NH2 9.1
67
72
C2 H5N2 H3 5.7
Ž
.
Ž .
CH3CCCN 35
HCCCCN 8.2
Ž
.
Ž .
C3H5CN 21
Ž .
C3H7CN 16
73
75
NC–CH2–CN 7.5
74
76
Ž
.
C3H3N5NH 13
Ž
.
.
Ž
.
.
77
79
C3H5N5NH 8.5
78
80
C4 H7 NH2 6.5
Ž
Ž .
4
Ž
C3H7 N5NH 6.6
C6
C4 H9 NH2 6.7
Ž
.
Ž .
Ž .
81
83
85
C3H7 N2 H3 12
C6 H2
C6 H4
C6 H6
3
82
84
86
HCCCCCN 46
Ž
.
Ž .
Ž .
CH3CCCCN 11
NCCCCN 8.1
Ž .
6
b
Ž .
6
Ž .
C6 H6
6
C2 H5CCCN 13
Ž
.
Ž
.
.
Ž
.
.
87
89
NC– CH2 2–CN 7.5
88
90
C4 H7 CN 5.6
Ž
Ž
C4 H5N5NH 6.4
C4 H9CN 7.4
Ž
.
Ž
.
91
93
95
98
C4 H7 N5NH 8.0
92
94
96
99
C5H9 NH2 3.6
Ž
.
Ž
.
C4 H9 N5NH 6.1
HCCCCCCN 5.2
CH3CCCCCN 7.2
Ž .
c
Ž
.
Ž
.
C4 H9 N2 H3 5.1
CH3CH2CCCCN 5.6
Ž
.
Ž .
C7 H8 4
C7 H8
4
Ž
.
Ž
.
.
Ž
.
Ž
.
100
102
104
106
108
110
115
123
128
138
CH3– CH2 2–CCCN 9.5
101
103
105
107
109
114
120
124
134
NC– CH2 3–CN 6.4
Ž
Ž
.
.
Ž
.
C5H9CN 5.2
C5H11CN 6.1
HCCCCCCCN 19
CH3CCCCCCN 5.0
CH3CH2CCCCCN 5.9
NC– CH2 4–CN 5.8
C6 H13N2 H3 5.0
C5H7 N5NH 4.8
C5H9 N5NH 13
NCCCCCCN 5.2
C5H11N2 H3 3.5
CH3– CH2 3–CCCN 8.4
CH3CCCCCCCN 16
CH3– CH2 2–CCCCCN 5.2
C8 H15NH2 8.5
Ž .
d
Ž
.
Ž
.
.
Ž .
3
C8 H4
Ž .
C8 H6 3
Ž
.
Ž
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž .
Ž
.
Ž
.
Ž
Ž
.
Ž
.
.
Ž
.
CH3– CH2 4–CCCN 7.1
Ž
Ž
.
CH3– CH2 3–CCCCCN 4.9
a The observed mrz due to the Liq-adduct.
b
d
,
c, and are possibly C5H5N, NCCCCCN, and C5H11N5NH, respectively.

(
)
736
T. FujiirChemical Physics Letters 313 1999 733–740
Ž
.
Ž
. Ž
.
and Ar 80% –C2 H2 20% vol–vol MW plasmas
under the same discharge conditions are shown in
Fig. 1. Series of masses differing by 14 mass units
the C2 H2rAr plasma were almost the same as those
w x
products were mainly hydrocarbons HCs , including
radicals such as CnH2 nq1 and CnH2 ny1, and some
molecules such as C4 H6 and C6 H6. Most of the
peaks that appeared in the C2 H2rN2 plasma had the
same mrz values as those that appeared in the pure
in previous experiments using pure C2 H2 8 . These
Ž
.
Ž
e.g., 34, 48, 62 and 76; 58, 72 and 86; 106, 120 and
134 are obvious.
The C2 H2rN2 plasma led to the formation of
many neutral species, while the products formed in
.
Table 2
Classification analysis of products formed by the MW discharge in a mixture of 20% C2 H2 and 80% N2. The representation is the same as
that described in Table 1
Type
Nitriles:
Chemical species
CnH2 nq1CNa
CnH2 ny1CN
CnH2 ny3CN
HCN 43 , CH3CN 100 , C2 H5CN 24 , C3H7CN 16 , C4 H9CN 7.4 , C5H11CN 6.1
Ž
.
Ž
Ž
Ž
Ž
.
Ž
Ž
.
Ž
Ž
.
Ž
Ž
.
Ž
Ž
.
CHCNc 7.4 , C2 H3CN 18 , C3H5CN 21 , C4 H7 CN 5.6 , C5H9CN 5.2
.
.
.
.
.
.
Ž
Ž
.
Ž
.
.
Ž
.
Ž
.
HCCCN 51 , CH3CCCN 35 , CH3CH2CCCN 13 , CH3– CH2 2–CCCN 9.5 , CH3– CH2
3
.
–CCCN 8.4 CH3– CH2
4
.
Ž
Ž
.
–CCCN 7.1
Ž
.
Ž
.
Ž
.
CnH2 ny5CN
CnH2 ny7CN
HCCCCN 8.2 , CH3–CCCCN 11 , CH3CH2CCCCN 5.6
Ž
.
Ž
Ž
.
Ž
.
HCCCCCN 46 , CH3CCCCCN 7.2 , CH3CH2CCCCCN 5.9 , CH3
Ž
.
Ž
.
.
Ž
.
– CH2 2–CCCCCN 5.2 , CH3– CH2 3–CCCCCN 4.9
HCCCCCCN 5.2 , CH3CCCCCCN 5.0
HCCCCCCCN 19 , CH3CCCCCCCN 16 , CH3CH2CCCCCN 8.5
CnH2 ny9CNb
CnH2 ny11CNb
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž .
NC–CN 10 , NC–CH2–CN 7.5 , NC– CH2 2–CN 7.5 , NC– CH2 3–CN 6.4 , NC– CH2 4–CN 5.8 ,
NC– CH2 n–CN
Ž
.
Ž
.
Ž
.
NC C[C nCN
NCCCCN 8.1 , NCCCCCCN 5.2
Amines:
CnH2 nq1NHb2
NH3 65 , CH3NH2 4.4 , C2 H5NH2 14 , C3H7 NH2 9.1 , C4 H9 NH2 6.7 ,
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
.
Ž
.
C5H11NH2 5.2 , C6 H13NH2 5.0
CHNH2 11 , C2 H3NH2 15 , C3H5NH2 7.7 , C4 H7 NH2 6.5 ,
C5H9 NH2 3.6 , C6 H11NH2 19 ,
CnH2 ny1NHb2
Ž
Ž
.
Ž
.
Ž
.
Ž
.
Ž .
Ž
.
Ž
.
C7 H13NH2 16 , C8 H15NH2 8.5
CnH2 ny3NHa2
Hydrazines:
Ž . Ž . Ž . Ž . Ž .
N2 H4 4.8 , CH3N2 H3 5.0 , C2 H5N2 H3 5.7 , C3H7 N2 H3 12 , C4 H9 N2 H3 5.1 ,
CnH2 nq1N2 H3
Ž
.
C5H11N2 H3 3.5
Ž
Ž
.
.
Ž
Ž
.
.
Ž
Ž
.
.
Ž
Ž
.
.
Ž
.
CnH2 nq1N5NH
CnH2 ny1N5NH
CnH2 ny3N5NH
CH3N5NH 21 , C2 H5N5NH 8.1 , C3H7 N5NH 6.6 , C4 H9 N5NH 6.1 , C5H11N5NH 5.2
CHN5NHd 86 , C2 H3N5NH 8.9 , C3H5N5NH 8.5 , C4 H7 N5NH 8.0 , C5H9 N5NH 13
Ž .
Ž .
Ž
.
Ž
.
Ž
.
C2 HN5NH 6 , C3H3N5NH 13 , C4 H5N5NH 6.4 , C5H7 N5NH 4.8
Ž . Ž .
Ž .
Others
H2C5NH 11 , H2 NCN 86 , NH2 43 ,
a The CnH2 ny3NH2 peaks are isobaric with the CnH2 nq1CN peaks of one lower n number. They were not distinguished in this study. We
assume from the presence of homologues that the latter were dominant.
b The CnH2 ny9CN and CnH2 ny11CN peaks are isobaric with the CnH2 nq1NH2 and CnH2 ny1NH2 peaks of the same n number,
respectively. We assume that both were present.
c
Ž
.
Possibly cyclic structure see context .
d Possibly cyclic structure, this molecule has the same mass number as H2 NCN.

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)
T. FujiirChemical Physics Letters 313 1999 733–740
737
C2 H2 plasma. However, their intensities were much
larger, indicating the production of many new types
of N-containing species in the C2 H2rN2 system.
The main peaks detected, their relative peak in-
tensities, and their assignments are given in Table 1.
Nitriles, amines, and hydrazines were identified.
Many less volatile species remained as a film of
solid on the flow tube wall. A black-brown solid was
also obtained, but this material has not been charac-
terized. Since the identification is based only on the
mass number, the assignment is not free of ambigu-
ity. For example, CH3CNLiq ions have the same
mrz value as C2 HNH2 Liq ions. Furthermore, the
relative abundance of isomeric pairs, such as HCNP
HNC and HCCCNPHCCNC, is inaccessible to mass
spectrometry.
Among many the nitriles produced, the
cyanopolyynes, HCnN, are particularly interesting
due to their linear conjugated structures, their biolog-
ical importance, and their abundance in the interstel-
lar medium. The well-known interstellar cyano-
Ž
. w
x
polyynes HCnN ns1, 3, 5, 7 18 can be formed
Ž
abundantly in the present system: HCN relative
intensity 43 , HCCCN 51 , HCCCCCN 46 , and
HCCCCCCCN 19 . In this study, the even numbers
of the HCnN series with n at 2, 4, and 6 were also
detected; however, their relative intensities were
much less than those of the cyanopolyynes with odd
carbon numbers.
.
Ž
.
Ž .
Ž
.
Ž
.
I observed other significant peaks at mrzs59,
83, and 107, which can be assigned to dicyanopoly-
Ž
.
acetylenes NC C[C CN with n at 0, 1, and 2.
n
The relative intensities of the peaks in both sys-
Cyanogen, NCCN, is well known for its production
Ž
w x
tems represent the monoisotopic intensities includ-
in high-temperature environments 19 and its postu-
lated presence in the interstellar medium. Since di-
cyanoacetylene, NCCCCN, was first reported in
1909, there have been surprisingly few studies of this
ing contributions from all the isotopes for a given
.
ion with the relative intensities normalized to 100
units for the base peak of the CH3CNLiq species in
w
x
the C2 H2rN2 plasma. With some exceptions, peaks
species 20,21 , despite being of interest as an un-
usual linear molecule which results in an extended p
Ž
with a height of -3% of the highest peak mrzs48
.
Ž
in the C2 H2rN2 plasma are not reported. When
orbital delocalization of the electrons along the
detecting neutral products by Liq ion attachment, the
sensitivity depends on the Liq affinity. Fortunately,
N-containing HC species have sufficiently high Liq
affinities to be attached at close to collision rates, so
little discrimination is expected.
whole molecule . The interest in these species can be
expected to increase in view of the recent observa-
tions of Grosser and Hirsch 1 : They were able to
produce large amounts of NC C[C CN molecules
by vaporizing graphite under helium in a reactor
designed for fullerene production in the presence of
cyanogen, C2 n2.
.
w x
Ž
.
n
3.2. Classification analysis
Ž
.
Ž
.
Dicyanoalkanes, NC CH2 nCN ns1–4 , are in-
teresting products found in this study that have not
been reported before. The fraction was fairly con-
stant, the observed intensity ratio of the mass lines
The observed peaks are classified in Table 2. The
MW discharge in C2 H2rN2 gave three types of
N-containing species: nitriles, amines, and hy-
drazines, and also possibly some HCs.
Ž
.
Ž
corresponding to the compounds NC CH2 nCN ns
1–4 produced was 100:100:85:77, and the intensity
.
3.2.1. Nitriles
Many products were formulated as CnH2 nq1CN
was relatively constant over the n values. I speculate
that these compounds will be synthesized in the
future.
Ž
.
Ž
.
Ž
ns1–5 , CnH2 ny1CN ns5 , CnH2 ny3CN ns
.
Ž
.
Ž
.
7 , CnH2 ny5CN ns3 , CnH2 ny7CN ns5 ,
Ž
.
Ž
.
CnH2 ny9CN ns3 , and CnH2 ny11CN ns3 . As
can be assumed from previous experimental results
w
x
17 , which showed that the dominant products from
MW discharge in a CH4rN2 mixture were nitriles,
3.2.2. Amines
The products included alkyl amines with single,
double, and triple bonds, with many homologous
members often present in roughly equal yields within
.
a factor of 4 . The higher homologues of
Ž
these homologues corresponding to additions of CH2
units may be saturated or unsaturated nitriles. Their
abundance seems to vary smoothly with chain length,
with CH3CN being most abundant.
.
Ž
Ž
.
CnH2 ny1NH2 ns6, 7, 8 were found in higher

(
)
738
T. FujiirChemical Physics Letters 313 1999 733–740
q
Ž .
C2 H3NH2 Liq mrzs50 , and CH3N5NHLi
fractions, mainly because the corresponding mass
lines were possibly enhanced with the same mass
signal as HCCCCCCCN, CH3CCCCCCN, and
C2 H5CCCCCCCN species.
Ž
.
mrzs51 against the gas composition is shown in
Fig. 2. The first 2 were chosen as the 2 most intense
species. The last 3 compounds represent the major
Ž
.
products classified as NC C[C CN, CnH2 ny1NH2 ,
n
3.2.3. Hydrazines
and CnH2 nq1N5NH molecules, respectively. The
homologous species generally followed similar varia-
tion patterns.
Some products were formulated as CnH2 nq1
Ž .
N H NH2 , CnH2 nq1N5NH, CnH2 ny1N5NH, and
Ž
CnH2 ny3N5NH. These homologues corresponding
to additions of CH2 units may be hydrazines. Again,
other assignments are possible.
The component ratio of 20% C2 H2 to 80% N2
was most favorable in terms of the total intensity of
adduct ions of the products and hence the classifica-
tion analysis in the previous section concerned only
this composition. However, it should be noted that
the major constituents each followed an entirely
different pattern. Although the present data are insuf-
ficient to arrive at a detailed explanation, a few facts
are worth noting. Plotting the intensities of the exam-
ined peaks against the C2 H2 ratio in the mixture gas
confirmed that the variations came from the addition
.
I also obtained other significant peaks at mrzs
36, which can be assigned to H2C5NHLiq. It is
suggested that hot NH2 or CN radicals generated by
dissociation of initial amine or nitrile products can
react with each other and with HC species to pro-
duce these unfamiliar organic compounds by way of
their recombination.
The peak assignment of these nitrogenated prod-
ucts is not free of ambiguity. The CnH2 nq1CN com-
pound peaks are isobaric with the CnH2 ny1 peaks of
one higher carbon number. Because HC radicals of
the CnH2 ny1 type were observed clearly in the
Ž
.
C2 H2rAr plasma see Fig. 1B , I tentatively specu-
late that both nitriles and HC radicals are formed.
Ž
.
Also, the CN CH2 nCN, CnH2 ny9CN, CnH2 ny1CN,
Ž .
Ž .
Cn H2 nq1N H –NH2 , Cn H2 ny1N H –NH2 , and
Ž .
CnH2 ny3N H –NH2 peaks are isobaric with the
CN–Nn –CNLiq, Cn H2 nq1NH2 , Cn H2 ny1NH2 ,
C n H 2 n q 1 N 5 N H , C n H 2 n y 1 N 5 N H , and
CnH2 ny3N5NH peaks of the same n number, re-
spectively. The CnH2 ny3NH2 peaks are isobaric
with the CnH2 nq1CN peaks of one lower carbon
number. In this study they were not distinguished.
3.3. Products Õs. gas component
It was instructive to study this system as a func-
tion of the feed gas component. A number of runs
were made to increase the total intensities of adduct
ions, SIadduct, issuing through the Liq ion attach-
ment reactions. Because the gas component affected
the Liq emission for each successive run, I consid-
Ž
.
ered the normalized concentrations % SIadduct of
the neutral species in the plasma for comparison
purposes.
Fig. 2. Liq-adduct intensity of the neutral products CH3CNLiq
q
q
Ž
.
Ž
.
Ž
mrz 48 , C2qH3NH2 Li
mrz 50 , CH3NsNHLi
mrz
The evolution of CH3CNLiq mrzs48 , HCC-
Ž
.
q
.
Ž
.
Ž .
mrz 59 , produced
51 , HCCCNLi
mrz 58 , and NCCNLi
CNLiq mrz s 58 , NCCNLi q mrz s 59 ,
Ž
.
Ž
.
in C2 H2 rN2 plasmas, plotted against gas composition.

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T. FujiirChemical Physics Letters 313 1999 733–740
739
w x
of acetylene to the system over the limited range, but
not in the same ratio.
As the percentage of C2 H2 increased, the peak
intensity of NCCNLiq increased to a maximum at
;10% C2 H2 and finally disappeared at around 30%
observed 8 as a major product of a C2 H2 discharge
plasma.
N) qC2 H3
™ CH2CNqH
D H o sy74 kcalrmol ,
.
Ž
1a
Ž
.
.
.
Ž
.
Ž
C2 H2. The CH3CN mrzs48 and HCCCN mrz
s58 peak heights increased monotonically with
increasing C2 H2 , reached their maximums at around
20% and 15% C2 H2 , respectively, and then de-
creased. In contrast to the behaviors of CH3CN
™ CH3CN
™ CNqC3
™ HCNqCH2
D H o sy167 kcalrmol ,
1b
1c
.
Ž
.
Ž
Ž
D H o sy46 kcalrmol ,
Ž
.
D H o sy60 kcalrmol ,
.
Ž
1d
Ž
.
Ž
.
Ž
.
mrzs48 and HCCCN mrzs58 , as the C2 H2
™ CHCNqH2
D H o sy75 kcalrmol .
component increased from 5% to 30% the % S of
C2 H3NH2 Liq and CH3N5NHLiq increased almost
linearly. These variations in behavior remain unex-
plained at this moment.
Ž
.
1e
Ž
.
This speculation is proved partially by the presence
of the major component, CH3CN. The cyano radical
is considered capable of a whole range of additional
w
x
reactions 23 . The assorted products of these reac-
tions would result in the widespread peaks.
3.4. Mechanism considerations
The most probable important reaction for the
production of amine and hydrazine species is thought
to be a reaction yielding an NH radical. It is well
A few types of reaction are briefly discussed to
model the present results. In many studies simulating
Titan’s atmosphere, it is reported that electric dis-
charge plasmas in a CH4rN2 gas mixture produce
many products including HCs, nitriles, amines, hy-
drazines, etc. Most of these were also observed in
the present C2 H2rN2 system and, in fact, these
studies have proved helpful in explaining the ob-
served results.
w
x
known 24 that NH can be produced exothermically
in hydrogen-active nitrogen systems. It is assumed
from the present observation of amines and hy-
drazines that NH radicals are rapidly converted into
these species in combination with many HC species.
3.5. Concluding remarks
From the present results, one would expect radical
chemistry to occur in the C2 H2rN2 discharge. Ac-
tive nitrogen atoms, N), are a primary radical prod-
The C2 H2rN2 MW discharge led to the produc-
tion of various kinds of chemical species, and effec-
tively demonstrated that the MW discharge is a
method for generating over 70 N-bearing products.
w
x
uct; it is well known 22 that electrons present in the
plasma should serve to produce active nitrogen atoms.
The following polymerization reaction starts with
this species.
Ž
.
They had the formulas Cm HnCN, NC CH2 nCN,
Ž .
NC C CN, Cm HnNH2 , and Cm HnN2 H3 with m
n
and n continuing on to 8 and 15. Direct observation
of these species was allowed by the measurement of
the Liq-adduct mass spectra. Further studies would
benefit from investigation of total pressure depen-
dencies, MW power variation and change of flow
rate. I will report them in the near future.
If N) is supplied, then the interaction between
N) and C2 H2 or other HCs is highly probable – the
free radical interaction with N) and other HCs is
highly exothermic, suggesting the production of the
larger N-bearing HC species. Reactions of radical-in-
volved condensations leading to polymeric products
may well dominate the chemistry of the C2 H2rN2
discharge.
Some interesting products found in this study
Ž
.
were H2C5NH and NC CH2 nCN. These compo-
nents are predicted to be possible future products.
The results may also have implications for our un-
derstanding of chemical evolution in the solar sys-
tem. Our results suggest that nitriles, amines and
hydrazines of higher molecular weight, and their
For instance, following are the thermodynami-
cally accessible channels and the corresponding en-
thalpies of reaction at Ts298 K for the reaction
between N) and C2 H3, which have been directly

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T. FujiirChemical Physics Letters 313 1999 733–740
w x
6
J.O.P. Pedersen, B.J. Opansky, S.R. Leone, J. Phys. Chem.
derivatives, such as cyano-acetylenes and dinitriles,
may have been synthesized as precursors of biologi-
cally important compounds in planetary lightning
and plasmas associated with meteor impacts which
may be acceptable analogs to MW plasmas.
Ž
.
97 1993 6822.
w x
7
T.C. Killian, J.M. Vrtilek, C.A. Goottlieb, E.W. Gottlieb, P.
Ž
.
Thaddeus, Astrophys. J. 365 1990 L89.
w x
Ž
.
8
T. Fujii, J. Appl. Phys. 82 1997 2056.
w x
9
A.M. Smith, C. Engel, A. Thoma, G. Schallmoser, B.E.
Ž
.
Wurfel, V.E. Bondybey, Chem. Phys. 184 1994 233.
w
w
x
10 J. Agreiter, A.M. Smith, M. Hartle, V.E. Bondybey, Chem.
Ž
.
Phys. Lett. 225 1994 87.
Acknowledgements
x
11 J. Agreiter, A.M. Smith, V.E. Bondybey, Chem. Phys. Lett.
Ž
.
241 1995 317.
This work was supported in part by the Japanese
Ministry of Education, Science and Culture under a
Grant-in-Aid for General Scientific Research
w
w
w
w
w
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Ž
.
12 T. Fujii, Anal. Chem. 64 1992 775.
13 T. Fujii, Chem. Phys. Lett. 191 1992 162.
14 T. Fujii, K. Syouji, J. Appl. Phys. 74 1993 3009.
15 T. Fujii, K. Syouji, J. Phys. Chem. 97 1993 11380.
16 T. Fujii, K. Syouji, Phys. Rev. E 49 1994 657.
17 T. Fujii, N. Arai, Proceedings of the 14th International Mass
x
Ž
.
Ž
x
.
Ž
.
04804033 . Thanks are due to N. Arai and T.
x
Ž
.
Yamada for their technical contributions.
x
Ž
.
x
Ž
Spectrometry Conference, Aug. 1997, Tampere in disk
.
form .
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