- Email: [email protected]
High-pressure mass spectrometric investigations of ion–molecule reactions in hydrogen sulfide and ammonia mixtures
ARTICLE IN PRESS
Vacuum 81 (2007) 1393–1397 www.elsevier.com/locate/vacuum
High-pressure mass spectrometric investigations of ion–molecule reactions in hydrogen sulfide and ammonia mixtures Leszek Wo´jcik, Artur Markowski Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin, Poland
Abstract The positive ion–molecule reactions in the mixtures of hydrogen sulfide and ammonia have been examined by means of quadrupole mass spectrometer with high-pressure ion source. The concentration of hydrogen sulfide in mixtures ranged from 10% to 90% with 10% + + increment. Mainly observed primary ions: NH+ (m/q ¼ 32) and H2S+ (m/q ¼ 34) were formed as the 2 (m/q ¼ 16), NH3 (m/q ¼ 17), S result of ionization and dissociative ionization by electrons with energy of 300 eV. For each mixture, major bimolecular ion–molecule + reactions have been identified at total pressure from 0.5 to 33.3 Pa. The main secondary ions: NH+ (m/q ¼ 35) and 4 (m/q ¼ 18), H3S NH3S+ (m/q ¼ 49) were observed. Relative intensities of ion currents for observed ions were determined as a function of total gas pressure inside ion source collision chamber, repeller potential and concentration of hydrogen sulfide in the mixture. r 2007 Elsevier Ltd. All rights reserved. Keywords: Mass spectrometry; Ion–molecule reactions; Hydrogen sulfide; Ammonia
1. Introduction Ammonia and hydrogen sulfide are considered as trace gases of the earth’s atmosphere. Their absolute volume are very low but they can significantly alter the earth’s weather and climate. Ion–molecule reactions involving these gases are very important processes which can take place at the upper layers of the atmosphere [1]. The authors present the results obtained for ion–molecule reactions in hydrogen sulfide–ammonia mixtures. The measurements were performed using a quadrupole mass spectrometer with the special ‘‘high-pressure’’ closed ion source with electron impact ionization constructed by L. Wo´jcik and K. Bederski, presented earlier [2]. Under experimental conditions gas pressure inside the collision chamber of the ion source was changed within the range from 0.5 to 33.3 Pa. The primary ions, initiated sequences of reactions, were formed in the collision chamber of the ion source by electrons with energy of 300 eV. All measurements were performed at a constant repeller potential equal 5 V. The ion–molecule reactions in hydroCorresponding author. Fax: +48 81 5376191.
E-mail address: [email protected] (L. Wo´jcik). 0042-207X/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2007.01.053
gen sulfide–ammonia mixtures have been studied for wide range of hydrogen sulfide concentration in the gas mixtures (10–90% with 10% increment). In the authors mind these measurements are the first for such a wide variations of H2S concentrations in the mixtures with ammonia. The ionic processes occurring in pure H2S [3–7,13], NH3 [4,8–15] and H2S–NH3 [16,17] mixtures have been studied by many investigators using various mass spectrometers and methods. 2. Experimental Measurement techniques and instrument have been described previously [14,18–22]. Investigated gases with high spectral purity H2S (99.8%) and NH3 (99.96%) were supplied by Praxair and Merck, respectively. The proper gas mixtures were prepared in the separate gas leak system. Total gas pressure inside the collision chamber of the ion source was controlled by an MKS Baratron capacitance manometer scaled in mTorr with precission of 70.5 mTorr. The ions produced as the result of ion–molecule reactions were observed with a quadrupole mass spectrometer detecting ions within the range of m/q from 1
ARTICLE IN PRESS L. Wo´jcik, A. Markowski / Vacuum 81 (2007) 1393–1397
1394
0.30
1.0
20% H2S + 80% NH3
20 % H2S + 80% NH3
0.9
0.25 Relative intensities Ii/ΣIi
Relative intensities Ii/ΣIi
0.8 0.7 0.6
NH3+ (m/q = 17)
0.5
+
NH4 (m/q = 18)
0.4
H3S+ (m/q = 35)
0.3 0.2
NH2+ (m/q = 16)
0.20
S+ (m/q = 32)
NH3S+ (m/q = 49)
0.15 0.10 0.05
0.1 0.00
0.0 0
4
8
12
16
20
24
28
32
0
36
4
8
12
20
24
28
32
36
28
32
36
0.30
1.0
40% H2S + 60% NH3
40% H2S + 60% NH3
0.9
0.25 Relative intensities Ii/ΣIi
0.8 Relative intensities Ii/ΣIi
16
Pressure [Pa]
Pressure [Pa]
0.7 0.6
NH3+ (m/q = 17)
0.5
NH4+ (m/q = 18)
0.4
H3S+ (m/q = 35)
0.3 0.2
NH2+ (m/q = 16)
0.20
S+ (m/q = 32) H2S+ (m/q = 34)
0.15
NH3S+ (m/q = 49)
0.10 0.05
0.1 0.0
0.00 0
4
8
12
16
20
24
28
32
36
Pressure [Pa]
0
4
8
12
16
20
24
Pressure [Pa]
Fig. 1. Relative ion currents as a function of total mixture pressure at constant repeller potential 5 V for four concentrations of ammonia (a) 20%, (b) 40%, (c) 60% and (d) 80% in the mixture with hydrogen sulfide.
to 400 u. High sensitivity of ion current measurements was achieved by application of 16-stage Balzers ion multiplier. The differential vacuum system makes it possible to evacuate the ion source and ion analyzer separately to maximize the gas pressure inside the ion source collision chamber, keeping the low pressure within the analyzer region.
hydrogen sulfide to form secondary ions according to the following reactions [3–7]: Sþ þ H2 S ! H2 Sþ þ S;
(1)
H2 Sþ þ H2 S ! H3 Sþ þ HS;
(2)
HSþ þ H2 S ! H3 Sþ þ S;
(3)
3. Results and discussion
Sþ þ H2 S ! S2 þ þ H2 :
(4)
At relatively low pressure of pure hydrogen sulfide inside the ion source collision chamber the main primary ions H2S+, HS+ and S+ were observed. As the pressure increases these primary ions react with neutral molecules of
At low pressures of ammonia in the collision chamber of + + the ion source (lower than 103 Pa) the NH+ 3 , NH2 , NH , + + 2+ H2 , H and NH3 ions are produced as the result of the ionization and dissociative ionization of ammonia by
ARTICLE IN PRESS L. Wo´jcik, A. Markowski / Vacuum 81 (2007) 1393–1397
0.25
1.0
0.20 Relative intensities Ii/ΣIi
0.8 Relative intensities Ii /ΣIi
60% H2S + 40% NH3
60% H2S + 40% NH3
0.9
0.7 0.6 NH3+ (m/q = 17)
0.5
NH4+ (m/q = 18)
0.4
H3S+ (m/q = 35)
0.3
1395
NH2+ (m/q = 16) S+ (m/q = 32) H2S+ (m/q = 34)
0.15
NH3S+ (m/q = 49)
0.10
0.05
0.2 0.1
0.00
0.0 0
4
8
12
16
20
24
28
32
36
0
4
8
12
Pressure [Pa] 1.0
0.30
80% H2S + 20% NH3
0.9
Relative intensities Ii/ΣIi
Relative intensities Ii/ΣIi
0.7 0.6 NH4+ (m/q = 18)
0.4
H2S+ (m/q = 34)
0.3
20
24
28
32
36
28
32
36
80% H2S + 20% NH3 NH2+ (m/q = 16)
0.25
0.8
0.5
16
Pressure [Pa]
0.2
NH3+ (m/q = 17) S+ (m/q = 32)
0.20
H3S+ (m/q = 35) NH3S+ (m/q = 49)
0.15 0.10 0.05
0.1 0.00
0.0 0
4
8
12
16
20
24
28
32
0
36
4
8
12
16
20
24
Pressure [Pa]
Pressure [Pa] Fig. 1. (Continued)
electrons. In an earlier work, Bederski et al. [23] determined the partial cross-sections for ionization of pure ammonia by electrons with energy from 25 to 1000 eV using cycloidal mass spectrometer with nearly 100% ion transmission coefficient. In pure ammonia when the pressure inside the ionization chamber of the ion source was 1.3 Pa, the main primary + ions NH+ were observed as the result of 3 and NH2 ionization and dissociative ionization by electrons [24]. These ions react rapidly with ammonia forming secondary ions. The following reactions can be observed for pure NH3 [4,8–15]:
NHþ þ NH3 ! NH4 þ þ N;
(7)
NH2 þ þ NH3 ! NH3 þ þ NH2 :
(8)
NH2 þ þ NH3 ! NH4 þ þ NH; NH3 þ þ NH3 ! NH4 þ þ NH2 ;
In the mixtures of hydrogen sulfide and ammonia, ion–molecule processes can take place according to the following reaction scheme [16]: NH3 þ þ H2 S ! NH4 þ þ HS;
(9)
NH3 þ þ H2 S ! H2 Sþ þ NH3 ;
(10)
(5)
NH3 þ þ H2 S ! H3 Sþ þ NH2 ;
(11)
(6)
NH2 þ þ H2 S ! H2 Sþ þ NH2 ;
(12)
ARTICLE IN PRESS 1396
L. Wo´jcik, A. Markowski / Vacuum 81 (2007) 1393–1397
NH2 þ þ H2 S ! H3 Sþ þ NH;
(13)
H2 Sþ þ NH3 ! NH3 þ þ H2 S;
(14)
H2 Sþ þ NH3 ! NH4 þ þ HS;
(15)
HSþ þ NH3 ! NH4 þ þ S;
(16)
HSþ þ NH3 ! NH3 þ þ H2 S;
(17)
HSþ þ NH3 ! NH2 þ þ H2 S;
(18)
HSþ þ NH3 ! NH3 Sþ þ H;
(19)
H2 Sþ þ NH3 ! H3 Sþ þ NH2 ;
(20)
H3 Sþ þ NH3 ! NH4 þ þ H2 S;
(21)
Sþ þ NH3 ! NH3 þ þ S:
(22)
Fig. 1 presents the results of ion–molecule reactions for four selected concentrations of hydrogen sulfide ((a) 20%, (b) 40%, (c) 60% and (d) 80%) in the hydrogen sulfide–ammonia mixtures. The repeller potential, for all measurements presented here, was 5 V. At low total pressure of the mixture the main primary + + ions observed are NH+ 2 (m/q ¼ 16), NH3 (m/q ¼ 17), S + (m/q ¼ 32) and H2S (m/q ¼ 34). These ions are produced by electrons in ammonia and hydrogen sulfide. The NH+ 2 and NH+ 3 ion currents have relatively high intensities for high ammonia concentrations in the mixtures and at relatively low total pressure. With the increasing total mixture pressure, the drop of relative ion currrents of + + NH+ could be observed. At a pressure 2 , NH3 and H2S + + higher than 3 Pa for NH+ 2 , 5 Pa for NH3 and 5 Pa H2S only small amounts of these ions can be observed. + The secondary ions at m/q ¼ 18, 35 and 49 (NH+ 4 , H 3S + and NH3S ) were observed as a result of the ion-molecule reactions (see scheme of reaction above). NH+ 4 are the most significant observed secondary ions. These ions were produced as the result of ion–molecule reactions (5–7,9,15,16,21). Relative ion current intensity for NH+ 4 ions achieved up to 97% of total ionization and then for further gas pressure increase, current intensities for this ions gradually decreases. As the concentration of ammonia in mixtures decreases maximum of relative currents intensities for NH+ 4 ions is shifted in the direction of higher total mixtures pressures. The relative ion currents at m/q ¼ 35 are formed from H3S+ ions. These ions come from reactions (2,3,11,13,20).
H3S+
NH3S+
Fig. 2. Results for main secondary ions H3S+ (at m/q ¼ 35) (a) and NH3S+ (at m/q ¼ 49) (b) as a function of hydrogen sulfide concentration and total pressure of the hydrogen sulfide–ammonia mixture.
The observed relative ion currents at m/q ¼ 49 are formed by NH3S+ ions. These ions are observed in experiment as the result of ion–molecule reaction (19). + + The primary ions H2S+, HS+, NH+ 3 , NH2 and NH are consumed in reactions (5–7, 9,15,16) leading to NH+ 4 ions production. For secondary ions H3S+ (at m/q ¼ 35) (a) and NH3S+ (at m/q ¼ 49) (b) ions, three-dimensional plots have been drawn to show the dependance of relative ion current intensities as a function of the gas pressure in the ion source collision chamber and on the H2S concentration in the mixture (see Fig. 2). 4. Conclusions The main destination of this paper were measurements of ion–molecule reactions, in hydrogen sulfide and ammonia mixtures, in order to examine reaction mechanisms. Measurements were made for different concentrations of ammonia and hydrogen sulfide in mixtures (from 90% H2S+10% NH3 to 10% H2S+90% NH3 with 10% increment) and total mixtures pressure changed from 0.5 to 33.3 Pa. The primary ions H2S+, HS+, S+ and NH+ 3 , + NH+ and NH were produced as the result of ionization 2 by electrons with energy of 300 eV. These ions react with neutral H2S and NH3 to form the secondary ions. The + mainly observed secondary ions were NH+ and for 4 , H 3S pressures higher than 4 Pa small amounts of NH3S+. Plots of relative ion currents intensities for observed primary and
ARTICLE IN PRESS L. Wo´jcik, A. Markowski / Vacuum 81 (2007) 1393–1397
secondary ions as a function of total mixtures pressure and for H3S+ and NH3S+ as a function of total pressure and concentration of H2S in particular mixtures, present evolution of ion–molecule reactions. Scheme of ion–molecule reactions in H2S and NH3 system was proposed by authors.
[10] [11] [12] [13] [14] [15] [16]
References [17] [1] Manahan SE. Environmental Chemistry. Michigan: Lewis Publishers; 1991. [2] Wo´jcik L, Bederski K. Ann Univ Mariae Curie-Sklodowska Sect AAA 1988/89;43/44:365. [3] Harrison AG, Thynne JCJ. Trans Faraday Soc 1966;62:3345. [4] Gupta SK, Jones EG, Harrison AG, Myher JJ. Can J Chem 1967;45:3107. [5] Beauchamp JL, Buttrill Jr. SE. J Chem Phys 1968;48:1783. [6] Ruska WEW, Franklin JL. Int J Mass Spectrom Ion Phys 1969;3:221. [7] Wo´jcik L, Markowski A. Vacuum 2005;78:193. [8] Ryan KR, Futrell JH. J Chem Phys 1965;42:824. [9] Ryan KR, Futrell JH. J Chem Phys 1965;43:3009.
[18] [19] [20] [21] [22] [23] [24]
1397
Harrison AG, Thynne JCJ. Trans Faraday Soc 1966;62:2804. Chupka WA, Russell E. J Chem Phys 1968;48:1527. Marx R, Mauclaire G. Int J Mass Spectrom Ion Phys 1973;10:213. Huntres WT, Pinizzotto RF. J Chem Phys 1973;59:4742. Wo´jcik L, Bederski K. Int J Mass Spectrom Ion Processes 1993;127;11. Ryan KR. J Chem Phys 1970;53:3844. Laudenslager JB, Huntress Jr. WT. Int J Mass Spectrom Ion Phys 1974;14:435. Wo´jcik L, Markowski A. Prace naukowe Politechniki Warszawskiej, Elektronika 2005;153:193. Wo´jcik L. Ann Univ Mariae Curie-Sklodowska Sect AAA 1999;54:74. Wo´jcik L, Markowski A. Prace naukowe Politechniki Warszawskiej, Elektronika 2002;143:149. Wo´jcik L, Markowski A. Vacuum 2003;70:391. Wo´jcik L, Markowski A. Vacuum 2005;78:235. Wo´jcik L, Bederski K. Int J Mass Spectrom Ion Process 1996;153:139. Bederski K, Wo´jcik L, Adamczyk B. Int J Mass Spectrom Ion Phys 1980;35:171. Wincel H. Int J Mass Spectrom Ion Phys 1972;9:267.
Vacuum 81 (2007) 1393–1397 www.elsevier.com/locate/vacuum
High-pressure mass spectrometric investigations of ion–molecule reactions in hydrogen sulfide and ammonia mixtures Leszek Wo´jcik, Artur Markowski Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin, Poland
Abstract The positive ion–molecule reactions in the mixtures of hydrogen sulfide and ammonia have been examined by means of quadrupole mass spectrometer with high-pressure ion source. The concentration of hydrogen sulfide in mixtures ranged from 10% to 90% with 10% + + increment. Mainly observed primary ions: NH+ (m/q ¼ 32) and H2S+ (m/q ¼ 34) were formed as the 2 (m/q ¼ 16), NH3 (m/q ¼ 17), S result of ionization and dissociative ionization by electrons with energy of 300 eV. For each mixture, major bimolecular ion–molecule + reactions have been identified at total pressure from 0.5 to 33.3 Pa. The main secondary ions: NH+ (m/q ¼ 35) and 4 (m/q ¼ 18), H3S NH3S+ (m/q ¼ 49) were observed. Relative intensities of ion currents for observed ions were determined as a function of total gas pressure inside ion source collision chamber, repeller potential and concentration of hydrogen sulfide in the mixture. r 2007 Elsevier Ltd. All rights reserved. Keywords: Mass spectrometry; Ion–molecule reactions; Hydrogen sulfide; Ammonia
1. Introduction Ammonia and hydrogen sulfide are considered as trace gases of the earth’s atmosphere. Their absolute volume are very low but they can significantly alter the earth’s weather and climate. Ion–molecule reactions involving these gases are very important processes which can take place at the upper layers of the atmosphere [1]. The authors present the results obtained for ion–molecule reactions in hydrogen sulfide–ammonia mixtures. The measurements were performed using a quadrupole mass spectrometer with the special ‘‘high-pressure’’ closed ion source with electron impact ionization constructed by L. Wo´jcik and K. Bederski, presented earlier [2]. Under experimental conditions gas pressure inside the collision chamber of the ion source was changed within the range from 0.5 to 33.3 Pa. The primary ions, initiated sequences of reactions, were formed in the collision chamber of the ion source by electrons with energy of 300 eV. All measurements were performed at a constant repeller potential equal 5 V. The ion–molecule reactions in hydroCorresponding author. Fax: +48 81 5376191.
E-mail address: [email protected] (L. Wo´jcik). 0042-207X/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2007.01.053
gen sulfide–ammonia mixtures have been studied for wide range of hydrogen sulfide concentration in the gas mixtures (10–90% with 10% increment). In the authors mind these measurements are the first for such a wide variations of H2S concentrations in the mixtures with ammonia. The ionic processes occurring in pure H2S [3–7,13], NH3 [4,8–15] and H2S–NH3 [16,17] mixtures have been studied by many investigators using various mass spectrometers and methods. 2. Experimental Measurement techniques and instrument have been described previously [14,18–22]. Investigated gases with high spectral purity H2S (99.8%) and NH3 (99.96%) were supplied by Praxair and Merck, respectively. The proper gas mixtures were prepared in the separate gas leak system. Total gas pressure inside the collision chamber of the ion source was controlled by an MKS Baratron capacitance manometer scaled in mTorr with precission of 70.5 mTorr. The ions produced as the result of ion–molecule reactions were observed with a quadrupole mass spectrometer detecting ions within the range of m/q from 1
ARTICLE IN PRESS L. Wo´jcik, A. Markowski / Vacuum 81 (2007) 1393–1397
1394
0.30
1.0
20% H2S + 80% NH3
20 % H2S + 80% NH3
0.9
0.25 Relative intensities Ii/ΣIi
Relative intensities Ii/ΣIi
0.8 0.7 0.6
NH3+ (m/q = 17)
0.5
+
NH4 (m/q = 18)
0.4
H3S+ (m/q = 35)
0.3 0.2
NH2+ (m/q = 16)
0.20
S+ (m/q = 32)
NH3S+ (m/q = 49)
0.15 0.10 0.05
0.1 0.00
0.0 0
4
8
12
16
20
24
28
32
0
36
4
8
12
20
24
28
32
36
28
32
36
0.30
1.0
40% H2S + 60% NH3
40% H2S + 60% NH3
0.9
0.25 Relative intensities Ii/ΣIi
0.8 Relative intensities Ii/ΣIi
16
Pressure [Pa]
Pressure [Pa]
0.7 0.6
NH3+ (m/q = 17)
0.5
NH4+ (m/q = 18)
0.4
H3S+ (m/q = 35)
0.3 0.2
NH2+ (m/q = 16)
0.20
S+ (m/q = 32) H2S+ (m/q = 34)
0.15
NH3S+ (m/q = 49)
0.10 0.05
0.1 0.0
0.00 0
4
8
12
16
20
24
28
32
36
Pressure [Pa]
0
4
8
12
16
20
24
Pressure [Pa]
Fig. 1. Relative ion currents as a function of total mixture pressure at constant repeller potential 5 V for four concentrations of ammonia (a) 20%, (b) 40%, (c) 60% and (d) 80% in the mixture with hydrogen sulfide.
to 400 u. High sensitivity of ion current measurements was achieved by application of 16-stage Balzers ion multiplier. The differential vacuum system makes it possible to evacuate the ion source and ion analyzer separately to maximize the gas pressure inside the ion source collision chamber, keeping the low pressure within the analyzer region.
hydrogen sulfide to form secondary ions according to the following reactions [3–7]: Sþ þ H2 S ! H2 Sþ þ S;
(1)
H2 Sþ þ H2 S ! H3 Sþ þ HS;
(2)
HSþ þ H2 S ! H3 Sþ þ S;
(3)
3. Results and discussion
Sþ þ H2 S ! S2 þ þ H2 :
(4)
At relatively low pressure of pure hydrogen sulfide inside the ion source collision chamber the main primary ions H2S+, HS+ and S+ were observed. As the pressure increases these primary ions react with neutral molecules of
At low pressures of ammonia in the collision chamber of + + the ion source (lower than 103 Pa) the NH+ 3 , NH2 , NH , + + 2+ H2 , H and NH3 ions are produced as the result of the ionization and dissociative ionization of ammonia by
ARTICLE IN PRESS L. Wo´jcik, A. Markowski / Vacuum 81 (2007) 1393–1397
0.25
1.0
0.20 Relative intensities Ii/ΣIi
0.8 Relative intensities Ii /ΣIi
60% H2S + 40% NH3
60% H2S + 40% NH3
0.9
0.7 0.6 NH3+ (m/q = 17)
0.5
NH4+ (m/q = 18)
0.4
H3S+ (m/q = 35)
0.3
1395
NH2+ (m/q = 16) S+ (m/q = 32) H2S+ (m/q = 34)
0.15
NH3S+ (m/q = 49)
0.10
0.05
0.2 0.1
0.00
0.0 0
4
8
12
16
20
24
28
32
36
0
4
8
12
Pressure [Pa] 1.0
0.30
80% H2S + 20% NH3
0.9
Relative intensities Ii/ΣIi
Relative intensities Ii/ΣIi
0.7 0.6 NH4+ (m/q = 18)
0.4
H2S+ (m/q = 34)
0.3
20
24
28
32
36
28
32
36
80% H2S + 20% NH3 NH2+ (m/q = 16)
0.25
0.8
0.5
16
Pressure [Pa]
0.2
NH3+ (m/q = 17) S+ (m/q = 32)
0.20
H3S+ (m/q = 35) NH3S+ (m/q = 49)
0.15 0.10 0.05
0.1 0.00
0.0 0
4
8
12
16
20
24
28
32
0
36
4
8
12
16
20
24
Pressure [Pa]
Pressure [Pa] Fig. 1. (Continued)
electrons. In an earlier work, Bederski et al. [23] determined the partial cross-sections for ionization of pure ammonia by electrons with energy from 25 to 1000 eV using cycloidal mass spectrometer with nearly 100% ion transmission coefficient. In pure ammonia when the pressure inside the ionization chamber of the ion source was 1.3 Pa, the main primary + ions NH+ were observed as the result of 3 and NH2 ionization and dissociative ionization by electrons [24]. These ions react rapidly with ammonia forming secondary ions. The following reactions can be observed for pure NH3 [4,8–15]:
NHþ þ NH3 ! NH4 þ þ N;
(7)
NH2 þ þ NH3 ! NH3 þ þ NH2 :
(8)
NH2 þ þ NH3 ! NH4 þ þ NH; NH3 þ þ NH3 ! NH4 þ þ NH2 ;
In the mixtures of hydrogen sulfide and ammonia, ion–molecule processes can take place according to the following reaction scheme [16]: NH3 þ þ H2 S ! NH4 þ þ HS;
(9)
NH3 þ þ H2 S ! H2 Sþ þ NH3 ;
(10)
(5)
NH3 þ þ H2 S ! H3 Sþ þ NH2 ;
(11)
(6)
NH2 þ þ H2 S ! H2 Sþ þ NH2 ;
(12)
ARTICLE IN PRESS 1396
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NH2 þ þ H2 S ! H3 Sþ þ NH;
(13)
H2 Sþ þ NH3 ! NH3 þ þ H2 S;
(14)
H2 Sþ þ NH3 ! NH4 þ þ HS;
(15)
HSþ þ NH3 ! NH4 þ þ S;
(16)
HSþ þ NH3 ! NH3 þ þ H2 S;
(17)
HSþ þ NH3 ! NH2 þ þ H2 S;
(18)
HSþ þ NH3 ! NH3 Sþ þ H;
(19)
H2 Sþ þ NH3 ! H3 Sþ þ NH2 ;
(20)
H3 Sþ þ NH3 ! NH4 þ þ H2 S;
(21)
Sþ þ NH3 ! NH3 þ þ S:
(22)
Fig. 1 presents the results of ion–molecule reactions for four selected concentrations of hydrogen sulfide ((a) 20%, (b) 40%, (c) 60% and (d) 80%) in the hydrogen sulfide–ammonia mixtures. The repeller potential, for all measurements presented here, was 5 V. At low total pressure of the mixture the main primary + + ions observed are NH+ 2 (m/q ¼ 16), NH3 (m/q ¼ 17), S + (m/q ¼ 32) and H2S (m/q ¼ 34). These ions are produced by electrons in ammonia and hydrogen sulfide. The NH+ 2 and NH+ 3 ion currents have relatively high intensities for high ammonia concentrations in the mixtures and at relatively low total pressure. With the increasing total mixture pressure, the drop of relative ion currrents of + + NH+ could be observed. At a pressure 2 , NH3 and H2S + + higher than 3 Pa for NH+ 2 , 5 Pa for NH3 and 5 Pa H2S only small amounts of these ions can be observed. + The secondary ions at m/q ¼ 18, 35 and 49 (NH+ 4 , H 3S + and NH3S ) were observed as a result of the ion-molecule reactions (see scheme of reaction above). NH+ 4 are the most significant observed secondary ions. These ions were produced as the result of ion–molecule reactions (5–7,9,15,16,21). Relative ion current intensity for NH+ 4 ions achieved up to 97% of total ionization and then for further gas pressure increase, current intensities for this ions gradually decreases. As the concentration of ammonia in mixtures decreases maximum of relative currents intensities for NH+ 4 ions is shifted in the direction of higher total mixtures pressures. The relative ion currents at m/q ¼ 35 are formed from H3S+ ions. These ions come from reactions (2,3,11,13,20).
H3S+
NH3S+
Fig. 2. Results for main secondary ions H3S+ (at m/q ¼ 35) (a) and NH3S+ (at m/q ¼ 49) (b) as a function of hydrogen sulfide concentration and total pressure of the hydrogen sulfide–ammonia mixture.
The observed relative ion currents at m/q ¼ 49 are formed by NH3S+ ions. These ions are observed in experiment as the result of ion–molecule reaction (19). + + The primary ions H2S+, HS+, NH+ 3 , NH2 and NH are consumed in reactions (5–7, 9,15,16) leading to NH+ 4 ions production. For secondary ions H3S+ (at m/q ¼ 35) (a) and NH3S+ (at m/q ¼ 49) (b) ions, three-dimensional plots have been drawn to show the dependance of relative ion current intensities as a function of the gas pressure in the ion source collision chamber and on the H2S concentration in the mixture (see Fig. 2). 4. Conclusions The main destination of this paper were measurements of ion–molecule reactions, in hydrogen sulfide and ammonia mixtures, in order to examine reaction mechanisms. Measurements were made for different concentrations of ammonia and hydrogen sulfide in mixtures (from 90% H2S+10% NH3 to 10% H2S+90% NH3 with 10% increment) and total mixtures pressure changed from 0.5 to 33.3 Pa. The primary ions H2S+, HS+, S+ and NH+ 3 , + NH+ and NH were produced as the result of ionization 2 by electrons with energy of 300 eV. These ions react with neutral H2S and NH3 to form the secondary ions. The + mainly observed secondary ions were NH+ and for 4 , H 3S pressures higher than 4 Pa small amounts of NH3S+. Plots of relative ion currents intensities for observed primary and
ARTICLE IN PRESS L. Wo´jcik, A. Markowski / Vacuum 81 (2007) 1393–1397
secondary ions as a function of total mixtures pressure and for H3S+ and NH3S+ as a function of total pressure and concentration of H2S in particular mixtures, present evolution of ion–molecule reactions. Scheme of ion–molecule reactions in H2S and NH3 system was proposed by authors.
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