- Email: [email protected]
High-pressure investigations of positive ion-molecule reactions in a mixtureof H2S and CH4
Vacuum 83 (2009) S173–S177
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
High-pressure investigations of positive ion-molecule reactions in a mixture of H2S and CH4 Leszek Wo´jcik*, Artur Markowski Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 June 2008 Received in revised form 16 January 2009 Accepted 30 January 2009
The positive ion-molecule reactions in the mixtures of hydrogen sulfide and methane have been examined by means of quadrupole mass spectrometer with the high-pressure ion source. The concentration of hydrogen sulfide in mixtures ranged from 10% to 90% with 10% increment. For each mixture major bimolecular ion-molecule reactions have been identified in the total pressure range from 0.7 to 33.3 Pa. The electron energy for all measurements was fixed at 300 eV and the repeller potential was þ þ þ maintained at 5 V. Relative intensities of ion currents for the observed ions Cþ, CHþ, CHþ 2 , CH3 , CH4 , CH5 , þ þ þ þ þ þ þ þ 34 þ þ þ þ C2Hþ 3 , C2H4 , C2H5 , S , HS , H2S , H3S , H3 S , CHS , CH3S , S2 , HS2 and H2S2 were determined as a function of total gas pressure inside the ion source collision chamber, repeller potential and concentration of methane in the mixture. Ó 2009 Published by Elsevier Ltd.
Keywords: Mass spectrometry Ion-molecule reactions Hydrogen sulfide Methane
1. Introduction Hydrogen sulfide and methane are important trace impurities of atmospheric air. These gases are emitted to the atmosphere as a consequence of natural biomass degradation (decay of proteins), biomass burning and motor exhaust. Sulfur compounds contribute to acidity of atmospheric rains. Like many gaseous pollutants H2S and CH4 can undergoes ionmolecule reactions in the upper layer of the earth atmosphere [1]. Knowledge about their mechanisms is very important for natural environment protection. The authors present the results obtained for ion-molecule reactions in the hydrogen sulfide–methane mixtures. Measurements were made by means of the quadrupole mass spectrometer with the special ‘‘high pressure’’ closed ion source with electron impact ionization constructed by L. Wo´jcik and K. Bederski [2]. During the measurements the gas pressure inside the collision chamber of the ion source has been changed from 0.7 to 33.3 Pa. The concentration of methane in mixtures was changed from 10% to 90% with 10% increments. Primary ions were produced by electrons emitted from the rhenium thermocathode and after that formed in beam by the system of ion source electrodes and then accelerated to the energy of 300 eV. All measurements were performed at a constant repeller potential equal to 5 V. These measurements, in the authors’ knowledge, are the first for such a wide area of methane concentrations in the mixtures with H2S.
* Corresponding author. Fax: þ48 81 5376191. E-mail address: [email protected] (L. Wo´jcik). 0042-207X/$ – see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.vacuum.2009.01.056
The ionic processes occurring in pure H2S [3–8] and CH4 [9–17] and also in the mixture of H2S–CH4 [18–20] were studied extensively by many investigators using various mass spectrometric techniques and methods. Specific reaction rate constants and cross-sections of the gaseous ion reactions occurring in the mixtures of methane with hydrogen sulfide were measured at a field strength of 10 V/cm by Field and Lampe. These studies were made by means of the cycloidal mass spectrometer [18]. Reactions of primary ions formed by electron impact in the mixtures of methane with hydrogen sulfide were also studied by Huntress, Pinizzotto and Laudenslager using ion-cyclotron resonance techniques. The reactions of primary ions were identified and their relative reaction rates measured using the double resonant cyclotron ejection method [20].
2. Experimental The technique of measurements and apparatus was described earlier [21–26]. The investigated gases of high spectral purity H2S (99.8%) and CH4 (99.99%) 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 measured by an MKS Baratron capacitance manometer scaled in mTorr with the accuracy of 0.5 mTorr. The ions produced as the result of ion-molecule reactions were analyzed by means of a quadrupole mass spectrometer detecting ions within the range of m/q from 1 to 400 u. Balzers type electron multiplier with the 16 dynodes and a high quality electrometer,
L. Wo´jcik, A. Markowski / Vacuum 83 (2009) S173–S177
S174
assured very well sensitivity of the ion detection system. The differential vacuum system made it possible to separate evacuation of the ion source and analyzer and to maximize the gas pressure inside the ion source collision chamber keeping the low pressure within the analyzer region. 3. Results and discussion At relatively low pressure of pure hydrogen sulfide inside the ion source collision chamber the main primary ions Sþ (m/q ¼ 32), HSþ (m/q ¼ 33) and H2Sþ (m/q ¼ 34) were observed. When the pressure gradually grows, primary ions start to react with neutral molecules of hydrogen sulfide to form secondary ions. As the result of interactions between primary H2Sþ ions and neutral H2S moleþ cules the following ions were observed: H3Sþ (m/q ¼ 35), H34 3 S (m/ þ þ þ q ¼ 37), S2 (m/q ¼ 64), HS2 (m/q ¼ 65), H2S2 (m/q ¼ 66) and H3Sþ 2 (m/q ¼ 67). Ion-molecule processes observed for pure hydrogen sulphide can be presented by the following reactions [3–7]:
* ½H2 SD * D H2 S / SD 2 D H2 D H2 S
(6)
When a gas pressure inside the high-pressure ion source was approximately equal to 1.33 Pa, the main observed primary ions þ þ were CHþ 2 , CH3 , CH4 . These ions come from ionization and fragmentation of methane. They react very fast with neutral molecules þ þ of the mixture and form the secondary ions CHþ 5 , C2H3 , C2H4 and C2Hþ 5. For high pressure of methane inside the ion source collision þ þ chamber, the primary ions CHþ 2 , CH3 and CH4 react with molecules of methane and the secondary ions are produced according to the following reactions [9–17]: D CHD 4 D CH4 / CH5 D CH3
(7)
D CHD 2 D CH4 / C2 H3 D H2 D H
(8)
D CHD 2 D CH4 / C2 H4 D H2
(9)
SD D H2 S / H2 SD D S
(1)
D CHD 3 D CH4 / C2 H5 D H2
(10)
H2 SD D H2 S / H3 SD D HS
(2)
D CHD 5 D CH4 / C2 H5 D 2H2
(11)
HSD D H2 S / H3 SD D S
(3)
D H2 S / SD 2 D H2
(4)
In the mixtures of hydrogen sulfide and methane, the following ion-molecule processes can take place according to the reaction scheme [18,20]:
(5)
H2 SD D CH4 / H3 SD D CH3
SD D H2 S $ ½H2 SD *
Relative intensities Ii/Σ ΣIi
a
20% CH4 + 80 % H2S
0.006
CH+ (m/q = 13) CH2+ (m/q = 14) CH5+ (m/q = 17) C2H5+ (m/q = 29)
0.004
0.002
0.000 0
4
8
12
16
CH3+ (m/q = 15) CH4+ (m/q = 16) S+ (m/q = 32) S2+ (m/q = 64)
0.08 0.06 0.04 0.02 0.00
0
4
20% CH4 + 80 % H2S
0.08
HS+ (m/q = 33) H334S+ (m/q = 37) CHS+ (m/q = 45) H2S2+ (m/q = 66)
0.06 0.04 0.02
0
4
8 12 16 20 24 28 32 36
Pressure [Pa]
Relative intensities Ii/ΣIi
1.0
0.10
Relative intensities Ii/ΣIi
20% CH4 + 80 % H2S
0.10
Pressure [Pa]
0.00
(12)
0.12
0.008
Relative intensities Ii/ΣIi
S
D
8 12 16 20 24 28 32 36
Pressure [Pa]
20% CH4 + 80 % H2S
0.9 0.8 0.7 0.6
H2S+ (m/q = 34) H3S+ (m/q = 35) CH3S+ (m/q = 47)
0.5 0.4 0.3 0.2 0.1 0.0 0
4
8
12 16 20 24 28 32 36
Pressure [Pa]
Fig. 1. Relative ion currents as a function of total mixture pressure at constant repeller potential 5 V for three concentrations of methane (a) 20%, (b) 50% and (c) 80% in the mixture with hydrogen sulfide.
L. Wo´jcik, A. Markowski / Vacuum 83 (2009) S173–S177
0.08
CH+ (m/q = 13) HS+ (m/q = 33) H334S+ (m/q = 37) H2S2+ (m/q = 66)
0.04
0.02
8 12 16 20 24 28 32 36
CH2+ (m/q = 14) S+ (m/q = 32) CHS+ (m/q = 45) HS2+ (m/q = 65)
0.04
0.02
0
4
0.02
0
4
8 12 16 20 24 28 32 36
Pressure [Pa]
1.0 0.8 0.7 0.6
H2S+ H3S+
(m/q = 34) (m/q = 35) CH3S+ (m/q = 47)
0.5 0.4 0.3 0.2 0.1 0
4
Pressure [Pa]
0.3
50% CH4 + 50% H2S
0.9
0.0
50% CH4 + 50% H2S 0.2
0.0
8 12 16 20 24 28 32 36
0.9
CH3+ (m/q = 15) CH4+ (m/q = 16)
0.1
0
Pressure [Pa]
c
CH5+ (m/q = 17) C2H3+ (m/q = 27) C2H5+ (m/q = 29) S2+ (m/q = 64)
0.04
8 12 16 20 24 28 32 36
Pressure [Pa]
50% CH4 + 50% H2S
0.06
0.00
0.00
Relative intensities Ii/ΣIi
4
Relative intensities Ii/ΣIi
0
Relative intensities Ii/Σ ΣIi
0.00
0.06
0.05
0.8
80% CH4 + 20% H2S
0.7 0.6 0.5
CH3+ (m/q = 15) CH4+ (m/q = 16) H2S+ (m/q = 34) H3S+ (m/q = 35)
0.4 0.3 0.2 0.1
Relative intensities Ii/ΣIi
0.06
0.08
50% CH4 + 50% H2S
Relative intensities Ii/ΣIi
Relative intensities Ii/ΣIi
50% CH4 + 50% H2S
2
4
Pressure [Pa]
6
80% CH4 + 20% H2S
0.04 C+ (m/q = 12) CH+ (m/q = 13) CH2+ (m/q = 14) S+ (m/q = 32) S2+ (m/q = 64)
0.03 0.02 0.01 0.00
0.0 0
4
0.05
8
Pressure [Pa]
0.04
C2H3+ (m/q = 27) HS+ (m/q = 33) H334S+ (m/q = 37) CHS+ (m/q = 45) H2S2+ (m/q = 66)
0.02 0.01
4
0.16
80% CH4 + 20% H2S
0.03
0
12 16 20 24 28 32 36
Relative intensities Ii/ΣIi
0.08
Relative intensities Ii/ΣIi
Relative intensities Ii/Σ ΣIi
b
S175
8 12 16 20 24 28 32 36
Pressure [Pa]
80% CH4 + 20% H2S CH5+ (m/q = 17) C2H4+ (m/q = 28) C2H5+ (m/q = 29) CH3S+ (m/q = 47)
0.12
0.08
0.04
0.00
0.00 0
4
8 12 16 20 24 28 32 36
Pressure [Pa]
0
4
8 12 16 20 24 28 32 36
Pressure [Pa] Fig. 1. (continued).
8
S176
L. Wo´jcik, A. Markowski / Vacuum 83 (2009) S173–S177
D CHD 5 D H2 S / H3 S D CH4
(13)
D C2 HD 5 D H2 S / H3 S D C2 H4
(14)
D CHD 3 D H2 S / CHS D 2H2
(15)
D CHD 4 D H2 S / CHS D 2H2 D H
(16)
D CHD 3 D H2 S / CH3 S D H2
(17)
Fig. 1 presents the results of ion-molecule reactions for three selected concentrations of methane ((a) 20%, (b) 50%, (c) 80%) in the hydrogen sulfide–methane mixtures. The repeller potential, for all measurements presented here, was 5 V. For high hydrogen sulfide concentrations in the mixtures (see Fig. 1), the Sþ (m/q ¼ 32), HSþ (m/q ¼ 33) and H2Sþ (m/q ¼ 34) ion currents reach high relative intensities, even at a low total pressure. With the increase of total mixture pressure, for the intensities of relative ion currents of Cþ (m/q ¼ 12), CHþ (m/q ¼ 13), CHþ 2 (m/ þ þ þ q ¼ 14), CHþ 3 (m/q ¼ 15), CH4 (m/q ¼ 16), S (m/q ¼ 32), HS (m/ þ q ¼ 33) and H2S (m/q ¼ 34), their decrease can be observed. For a pressure higher than about 16 Pa, only small amounts of ions Cþ, þ þ þ þ þ CHþ, CHþ 2 , CH3 , CH4 , S , HS and H2S can be observed. The secondary ions at m/q ¼ 17, 27, 28, 29, 35, 37, 45, 47, 64, 65 þ þ þ 34 þ þ þ þ þ þ and 66 (CHþ 5 , C2H3 , C2H4 , C2H5 , H3S , H3 S , CHS , CH3S , S2 , HS2 and H2Sþ 2 ) were observed as the result of ion-molecule reactions (see the scheme of reactions above). H3Sþ are the most significant secondary ions observed. Relative ion current intensity for these ions achieved almost 90% of the total ionization, at a pressure approximately equal to 6 Pa, and then for further gas pressure increase, the saturation for this ion current can be observed. These ions were produced as the result of ion-molecule reactions (2), (3), (12)–(14). Relative current intensities for Sþ 2 reach the maximum at a pressure near 8 Pa and then for the further gas pressure increase, plateau for this ion current can be observed. These ions were produced as the result of ion-molecule reactions (2) and (6). þ þ þ The secondary ions CHþ 5 , C2H3 , C2H4 and C2H5 come from reactions (7)–(11). Their relative ion current grows with the increasing of methane concentration in the investigated mixtures. þ The CHþ 3 (m/q ¼ 15) and CH4 (m/q ¼ 16) ion currents have relatively high intensities for high methane concentrations in the mixtures even at a relatively low total pressure. Only small amounts of CHSþ (m/q ¼ 45) equal (0.2–0.8% of total ionization), CH3Sþ (4–8% of total ionization) (m/q ¼ 47), HSþ 2 (0.5% of total ionization) (m/q ¼ 65) and H2Sþ 2 (0.1–0.7% of total ionization) (m/q ¼ 66) were observed during the experiment as the result of ion-molecule reactions (15)–(17). þ For the secondary ions (a) Sþ 2 (m/q ¼ 64) and (b) H3S (m/q ¼ 35) ions, three-dimensional plots have been drawn to show the dependence of relative ion current intensities as a function of the gas pressure in the ion source collision chamber and on the methane concentration in the mixture (see Fig. 2). For small concentrations of H2S in the mixture with methane (10% H2S þ 90%CH4) the relative intensity of Sþ 2 ion current hardly depends on the total pressure of the mixture inside the ionization chamber. The relative intensities of the current Sþ 2 grow with the growth of the concentration of H2S and also the influence of the pressure on these values can be seen. The relative ion current intensity of Sþ 2 gradually grows as the total mixture pressure increases. In the case of H3Sþ ions, their relative intensities clearly depend on the total pressure of the mixture, particularly in the region of low pressures. One can also observe considerably smaller increase of the relative intensity of these ions as a function of H2S concentration in the mixture. Relative intensity achieves the maximum
a
b
þ Fig. 2. Results for secondary ions (a) Sþ 2 (at m/q ¼ 64) and (b) H3S (at m/q ¼ 35) as a function of methane concentration and total pressure of the hydrogen sulfide– methane mixture.
values for both maximum total pressure and almost maximum H2S concentration. 4. Conclusions For a total gas pressure higher than about 16 Pa, only small þ þ þ þ amounts of primary ions Cþ, CHþ, CHþ 2 , CH3 , CH4 , S , HSþ, H2S can be observed. They react very fast to form secondary ions (CHþ 5, þ þ 34 þ þ þ þ þ þ þ C2Hþ 3 , C2H4 , C2H5 , H3S , H3 S , CHS , CH3S , S2 , HS2 and H2S2 ). þ The relative intensities of CHSþ, CH3Sþ, HSþ 2 and H2S2 observed during the experiment are very low and their contribution to the total ionization is only a fraction of the percent. The most intense H3Sþ ions were produced according to reactions (2), (3), (12)–(14). Relative abundances of these ions reach almost 90% of the total ionization, at a pressure approximately equal to 6 Pa, then for further gas pressure increase, the saturation for this ion current can be observed. The growth in relative intensity of these ions can be observed as a function of H2S concentration in the mixture. Sþ 2 ion current intensities are almost independent of the total pressure of the mixture inside the ionization chamber for low H2S concentration. Relative intensity of Sþ 2 ion current increases with the growth of H2S concentration. Similarly, the increase of relative Sþ 2 ion current can be observed as a function of total mixture pressure (particularly in low pressure range). References [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.
L. Wo´jcik, A. Markowski / Vacuum 83 (2009) S173–S177 [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
Harrison AG, Thynne JCJ. Trans Faraday Soc 1966;62:3345. Gupta SK, Jones EG, Harrison AG, Myher JJ. Can J Chem 1967;45:3107. Beauchamp JL, Buttrill Jr SE. J Chem Phys 1968;48:1783. Ruska WEW, Franklin JL. Int J Mass Spectrom Ion Phys 1969;3:221. Wo´jcik L, Markowski A. Vacuum 2005;78:193. Huntres WT, Pinizzotto RF. J Chem Phys 1973;59:4742. Field FH, Franklin JL, Lampe FW. J Am Chem Soc 1957;79:2419. Wexler S, Jesse N. J Am Chem Soc 1962;84:3425. Field FH, Franklin JL, Munson MSB. J Am Chem Soc 1963;85:3575. Studniarz SA, Franklin JL. J Chem Phys 1968;49:319. Clow RP, Futrell JH. Int J Mass Spectrom Ion Phys 1970;4:165. Herod AA, Harrison AG. Int J Mass Spectrom Ion Phys 1970;4:415. McIver RT, Dunbar RC. Int J Mass Spectrom Ion Phys 1971;7:471.
[16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
S177
Anicich VG, Bowers MT. Int J Mass Spectrom Ion Phys 1973;11:329. Michalak L, Adamczyk B. Int J Mass Spectrom Ion Processes 1988;85:319. Field FH, Lampe FW. J Am Chem Soc 1958;80:5583. Bennett SL, Field FH. J Am Chem Soc 1972;94:6305. Huntress Jr WT, Pinizzotto Jr RF, Laudenslager JB. J Am Chem Soc 1973;95:4107. Wo´jcik L, Bederski K. Int J Mass Spectrom Ion Processes 1993;127:11. 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 Processes 1996;153:139.
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
High-pressure investigations of positive ion-molecule reactions in a mixture of H2S and CH4 Leszek Wo´jcik*, Artur Markowski Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 June 2008 Received in revised form 16 January 2009 Accepted 30 January 2009
The positive ion-molecule reactions in the mixtures of hydrogen sulfide and methane have been examined by means of quadrupole mass spectrometer with the high-pressure ion source. The concentration of hydrogen sulfide in mixtures ranged from 10% to 90% with 10% increment. For each mixture major bimolecular ion-molecule reactions have been identified in the total pressure range from 0.7 to 33.3 Pa. The electron energy for all measurements was fixed at 300 eV and the repeller potential was þ þ þ maintained at 5 V. Relative intensities of ion currents for the observed ions Cþ, CHþ, CHþ 2 , CH3 , CH4 , CH5 , þ þ þ þ þ þ þ þ 34 þ þ þ þ C2Hþ 3 , C2H4 , C2H5 , S , HS , H2S , H3S , H3 S , CHS , CH3S , S2 , HS2 and H2S2 were determined as a function of total gas pressure inside the ion source collision chamber, repeller potential and concentration of methane in the mixture. Ó 2009 Published by Elsevier Ltd.
Keywords: Mass spectrometry Ion-molecule reactions Hydrogen sulfide Methane
1. Introduction Hydrogen sulfide and methane are important trace impurities of atmospheric air. These gases are emitted to the atmosphere as a consequence of natural biomass degradation (decay of proteins), biomass burning and motor exhaust. Sulfur compounds contribute to acidity of atmospheric rains. Like many gaseous pollutants H2S and CH4 can undergoes ionmolecule reactions in the upper layer of the earth atmosphere [1]. Knowledge about their mechanisms is very important for natural environment protection. The authors present the results obtained for ion-molecule reactions in the hydrogen sulfide–methane mixtures. Measurements were made by means of the quadrupole mass spectrometer with the special ‘‘high pressure’’ closed ion source with electron impact ionization constructed by L. Wo´jcik and K. Bederski [2]. During the measurements the gas pressure inside the collision chamber of the ion source has been changed from 0.7 to 33.3 Pa. The concentration of methane in mixtures was changed from 10% to 90% with 10% increments. Primary ions were produced by electrons emitted from the rhenium thermocathode and after that formed in beam by the system of ion source electrodes and then accelerated to the energy of 300 eV. All measurements were performed at a constant repeller potential equal to 5 V. These measurements, in the authors’ knowledge, are the first for such a wide area of methane concentrations in the mixtures with H2S.
* Corresponding author. Fax: þ48 81 5376191. E-mail address: [email protected] (L. Wo´jcik). 0042-207X/$ – see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.vacuum.2009.01.056
The ionic processes occurring in pure H2S [3–8] and CH4 [9–17] and also in the mixture of H2S–CH4 [18–20] were studied extensively by many investigators using various mass spectrometric techniques and methods. Specific reaction rate constants and cross-sections of the gaseous ion reactions occurring in the mixtures of methane with hydrogen sulfide were measured at a field strength of 10 V/cm by Field and Lampe. These studies were made by means of the cycloidal mass spectrometer [18]. Reactions of primary ions formed by electron impact in the mixtures of methane with hydrogen sulfide were also studied by Huntress, Pinizzotto and Laudenslager using ion-cyclotron resonance techniques. The reactions of primary ions were identified and their relative reaction rates measured using the double resonant cyclotron ejection method [20].
2. Experimental The technique of measurements and apparatus was described earlier [21–26]. The investigated gases of high spectral purity H2S (99.8%) and CH4 (99.99%) 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 measured by an MKS Baratron capacitance manometer scaled in mTorr with the accuracy of 0.5 mTorr. The ions produced as the result of ion-molecule reactions were analyzed by means of a quadrupole mass spectrometer detecting ions within the range of m/q from 1 to 400 u. Balzers type electron multiplier with the 16 dynodes and a high quality electrometer,
L. Wo´jcik, A. Markowski / Vacuum 83 (2009) S173–S177
S174
assured very well sensitivity of the ion detection system. The differential vacuum system made it possible to separate evacuation of the ion source and analyzer and to maximize the gas pressure inside the ion source collision chamber keeping the low pressure within the analyzer region. 3. Results and discussion At relatively low pressure of pure hydrogen sulfide inside the ion source collision chamber the main primary ions Sþ (m/q ¼ 32), HSþ (m/q ¼ 33) and H2Sþ (m/q ¼ 34) were observed. When the pressure gradually grows, primary ions start to react with neutral molecules of hydrogen sulfide to form secondary ions. As the result of interactions between primary H2Sþ ions and neutral H2S moleþ cules the following ions were observed: H3Sþ (m/q ¼ 35), H34 3 S (m/ þ þ þ q ¼ 37), S2 (m/q ¼ 64), HS2 (m/q ¼ 65), H2S2 (m/q ¼ 66) and H3Sþ 2 (m/q ¼ 67). Ion-molecule processes observed for pure hydrogen sulphide can be presented by the following reactions [3–7]:
* ½H2 SD * D H2 S / SD 2 D H2 D H2 S
(6)
When a gas pressure inside the high-pressure ion source was approximately equal to 1.33 Pa, the main observed primary ions þ þ were CHþ 2 , CH3 , CH4 . These ions come from ionization and fragmentation of methane. They react very fast with neutral molecules þ þ of the mixture and form the secondary ions CHþ 5 , C2H3 , C2H4 and C2Hþ 5. For high pressure of methane inside the ion source collision þ þ chamber, the primary ions CHþ 2 , CH3 and CH4 react with molecules of methane and the secondary ions are produced according to the following reactions [9–17]: D CHD 4 D CH4 / CH5 D CH3
(7)
D CHD 2 D CH4 / C2 H3 D H2 D H
(8)
D CHD 2 D CH4 / C2 H4 D H2
(9)
SD D H2 S / H2 SD D S
(1)
D CHD 3 D CH4 / C2 H5 D H2
(10)
H2 SD D H2 S / H3 SD D HS
(2)
D CHD 5 D CH4 / C2 H5 D 2H2
(11)
HSD D H2 S / H3 SD D S
(3)
D H2 S / SD 2 D H2
(4)
In the mixtures of hydrogen sulfide and methane, the following ion-molecule processes can take place according to the reaction scheme [18,20]:
(5)
H2 SD D CH4 / H3 SD D CH3
SD D H2 S $ ½H2 SD *
Relative intensities Ii/Σ ΣIi
a
20% CH4 + 80 % H2S
0.006
CH+ (m/q = 13) CH2+ (m/q = 14) CH5+ (m/q = 17) C2H5+ (m/q = 29)
0.004
0.002
0.000 0
4
8
12
16
CH3+ (m/q = 15) CH4+ (m/q = 16) S+ (m/q = 32) S2+ (m/q = 64)
0.08 0.06 0.04 0.02 0.00
0
4
20% CH4 + 80 % H2S
0.08
HS+ (m/q = 33) H334S+ (m/q = 37) CHS+ (m/q = 45) H2S2+ (m/q = 66)
0.06 0.04 0.02
0
4
8 12 16 20 24 28 32 36
Pressure [Pa]
Relative intensities Ii/ΣIi
1.0
0.10
Relative intensities Ii/ΣIi
20% CH4 + 80 % H2S
0.10
Pressure [Pa]
0.00
(12)
0.12
0.008
Relative intensities Ii/ΣIi
S
D
8 12 16 20 24 28 32 36
Pressure [Pa]
20% CH4 + 80 % H2S
0.9 0.8 0.7 0.6
H2S+ (m/q = 34) H3S+ (m/q = 35) CH3S+ (m/q = 47)
0.5 0.4 0.3 0.2 0.1 0.0 0
4
8
12 16 20 24 28 32 36
Pressure [Pa]
Fig. 1. Relative ion currents as a function of total mixture pressure at constant repeller potential 5 V for three concentrations of methane (a) 20%, (b) 50% and (c) 80% in the mixture with hydrogen sulfide.
L. Wo´jcik, A. Markowski / Vacuum 83 (2009) S173–S177
0.08
CH+ (m/q = 13) HS+ (m/q = 33) H334S+ (m/q = 37) H2S2+ (m/q = 66)
0.04
0.02
8 12 16 20 24 28 32 36
CH2+ (m/q = 14) S+ (m/q = 32) CHS+ (m/q = 45) HS2+ (m/q = 65)
0.04
0.02
0
4
0.02
0
4
8 12 16 20 24 28 32 36
Pressure [Pa]
1.0 0.8 0.7 0.6
H2S+ H3S+
(m/q = 34) (m/q = 35) CH3S+ (m/q = 47)
0.5 0.4 0.3 0.2 0.1 0
4
Pressure [Pa]
0.3
50% CH4 + 50% H2S
0.9
0.0
50% CH4 + 50% H2S 0.2
0.0
8 12 16 20 24 28 32 36
0.9
CH3+ (m/q = 15) CH4+ (m/q = 16)
0.1
0
Pressure [Pa]
c
CH5+ (m/q = 17) C2H3+ (m/q = 27) C2H5+ (m/q = 29) S2+ (m/q = 64)
0.04
8 12 16 20 24 28 32 36
Pressure [Pa]
50% CH4 + 50% H2S
0.06
0.00
0.00
Relative intensities Ii/ΣIi
4
Relative intensities Ii/ΣIi
0
Relative intensities Ii/Σ ΣIi
0.00
0.06
0.05
0.8
80% CH4 + 20% H2S
0.7 0.6 0.5
CH3+ (m/q = 15) CH4+ (m/q = 16) H2S+ (m/q = 34) H3S+ (m/q = 35)
0.4 0.3 0.2 0.1
Relative intensities Ii/ΣIi
0.06
0.08
50% CH4 + 50% H2S
Relative intensities Ii/ΣIi
Relative intensities Ii/ΣIi
50% CH4 + 50% H2S
2
4
Pressure [Pa]
6
80% CH4 + 20% H2S
0.04 C+ (m/q = 12) CH+ (m/q = 13) CH2+ (m/q = 14) S+ (m/q = 32) S2+ (m/q = 64)
0.03 0.02 0.01 0.00
0.0 0
4
0.05
8
Pressure [Pa]
0.04
C2H3+ (m/q = 27) HS+ (m/q = 33) H334S+ (m/q = 37) CHS+ (m/q = 45) H2S2+ (m/q = 66)
0.02 0.01
4
0.16
80% CH4 + 20% H2S
0.03
0
12 16 20 24 28 32 36
Relative intensities Ii/ΣIi
0.08
Relative intensities Ii/ΣIi
Relative intensities Ii/Σ ΣIi
b
S175
8 12 16 20 24 28 32 36
Pressure [Pa]
80% CH4 + 20% H2S CH5+ (m/q = 17) C2H4+ (m/q = 28) C2H5+ (m/q = 29) CH3S+ (m/q = 47)
0.12
0.08
0.04
0.00
0.00 0
4
8 12 16 20 24 28 32 36
Pressure [Pa]
0
4
8 12 16 20 24 28 32 36
Pressure [Pa] Fig. 1. (continued).
8
S176
L. Wo´jcik, A. Markowski / Vacuum 83 (2009) S173–S177
D CHD 5 D H2 S / H3 S D CH4
(13)
D C2 HD 5 D H2 S / H3 S D C2 H4
(14)
D CHD 3 D H2 S / CHS D 2H2
(15)
D CHD 4 D H2 S / CHS D 2H2 D H
(16)
D CHD 3 D H2 S / CH3 S D H2
(17)
Fig. 1 presents the results of ion-molecule reactions for three selected concentrations of methane ((a) 20%, (b) 50%, (c) 80%) in the hydrogen sulfide–methane mixtures. The repeller potential, for all measurements presented here, was 5 V. For high hydrogen sulfide concentrations in the mixtures (see Fig. 1), the Sþ (m/q ¼ 32), HSþ (m/q ¼ 33) and H2Sþ (m/q ¼ 34) ion currents reach high relative intensities, even at a low total pressure. With the increase of total mixture pressure, for the intensities of relative ion currents of Cþ (m/q ¼ 12), CHþ (m/q ¼ 13), CHþ 2 (m/ þ þ þ q ¼ 14), CHþ 3 (m/q ¼ 15), CH4 (m/q ¼ 16), S (m/q ¼ 32), HS (m/ þ q ¼ 33) and H2S (m/q ¼ 34), their decrease can be observed. For a pressure higher than about 16 Pa, only small amounts of ions Cþ, þ þ þ þ þ CHþ, CHþ 2 , CH3 , CH4 , S , HS and H2S can be observed. The secondary ions at m/q ¼ 17, 27, 28, 29, 35, 37, 45, 47, 64, 65 þ þ þ 34 þ þ þ þ þ þ and 66 (CHþ 5 , C2H3 , C2H4 , C2H5 , H3S , H3 S , CHS , CH3S , S2 , HS2 and H2Sþ 2 ) were observed as the result of ion-molecule reactions (see the scheme of reactions above). H3Sþ are the most significant secondary ions observed. Relative ion current intensity for these ions achieved almost 90% of the total ionization, at a pressure approximately equal to 6 Pa, and then for further gas pressure increase, the saturation for this ion current can be observed. These ions were produced as the result of ion-molecule reactions (2), (3), (12)–(14). Relative current intensities for Sþ 2 reach the maximum at a pressure near 8 Pa and then for the further gas pressure increase, plateau for this ion current can be observed. These ions were produced as the result of ion-molecule reactions (2) and (6). þ þ þ The secondary ions CHþ 5 , C2H3 , C2H4 and C2H5 come from reactions (7)–(11). Their relative ion current grows with the increasing of methane concentration in the investigated mixtures. þ The CHþ 3 (m/q ¼ 15) and CH4 (m/q ¼ 16) ion currents have relatively high intensities for high methane concentrations in the mixtures even at a relatively low total pressure. Only small amounts of CHSþ (m/q ¼ 45) equal (0.2–0.8% of total ionization), CH3Sþ (4–8% of total ionization) (m/q ¼ 47), HSþ 2 (0.5% of total ionization) (m/q ¼ 65) and H2Sþ 2 (0.1–0.7% of total ionization) (m/q ¼ 66) were observed during the experiment as the result of ion-molecule reactions (15)–(17). þ For the secondary ions (a) Sþ 2 (m/q ¼ 64) and (b) H3S (m/q ¼ 35) ions, three-dimensional plots have been drawn to show the dependence of relative ion current intensities as a function of the gas pressure in the ion source collision chamber and on the methane concentration in the mixture (see Fig. 2). For small concentrations of H2S in the mixture with methane (10% H2S þ 90%CH4) the relative intensity of Sþ 2 ion current hardly depends on the total pressure of the mixture inside the ionization chamber. The relative intensities of the current Sþ 2 grow with the growth of the concentration of H2S and also the influence of the pressure on these values can be seen. The relative ion current intensity of Sþ 2 gradually grows as the total mixture pressure increases. In the case of H3Sþ ions, their relative intensities clearly depend on the total pressure of the mixture, particularly in the region of low pressures. One can also observe considerably smaller increase of the relative intensity of these ions as a function of H2S concentration in the mixture. Relative intensity achieves the maximum
a
b
þ Fig. 2. Results for secondary ions (a) Sþ 2 (at m/q ¼ 64) and (b) H3S (at m/q ¼ 35) as a function of methane concentration and total pressure of the hydrogen sulfide– methane mixture.
values for both maximum total pressure and almost maximum H2S concentration. 4. Conclusions For a total gas pressure higher than about 16 Pa, only small þ þ þ þ amounts of primary ions Cþ, CHþ, CHþ 2 , CH3 , CH4 , S , HSþ, H2S can be observed. They react very fast to form secondary ions (CHþ 5, þ þ 34 þ þ þ þ þ þ þ C2Hþ 3 , C2H4 , C2H5 , H3S , H3 S , CHS , CH3S , S2 , HS2 and H2S2 ). þ The relative intensities of CHSþ, CH3Sþ, HSþ 2 and H2S2 observed during the experiment are very low and their contribution to the total ionization is only a fraction of the percent. The most intense H3Sþ ions were produced according to reactions (2), (3), (12)–(14). Relative abundances of these ions reach almost 90% of the total ionization, at a pressure approximately equal to 6 Pa, then for further gas pressure increase, the saturation for this ion current can be observed. The growth in relative intensity of these ions can be observed as a function of H2S concentration in the mixture. Sþ 2 ion current intensities are almost independent of the total pressure of the mixture inside the ionization chamber for low H2S concentration. Relative intensity of Sþ 2 ion current increases with the growth of H2S concentration. Similarly, the increase of relative Sþ 2 ion current can be observed as a function of total mixture pressure (particularly in low pressure range). References [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.
L. Wo´jcik, A. Markowski / Vacuum 83 (2009) S173–S177 [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
Harrison AG, Thynne JCJ. Trans Faraday Soc 1966;62:3345. Gupta SK, Jones EG, Harrison AG, Myher JJ. Can J Chem 1967;45:3107. Beauchamp JL, Buttrill Jr SE. J Chem Phys 1968;48:1783. Ruska WEW, Franklin JL. Int J Mass Spectrom Ion Phys 1969;3:221. Wo´jcik L, Markowski A. Vacuum 2005;78:193. Huntres WT, Pinizzotto RF. J Chem Phys 1973;59:4742. Field FH, Franklin JL, Lampe FW. J Am Chem Soc 1957;79:2419. Wexler S, Jesse N. J Am Chem Soc 1962;84:3425. Field FH, Franklin JL, Munson MSB. J Am Chem Soc 1963;85:3575. Studniarz SA, Franklin JL. J Chem Phys 1968;49:319. Clow RP, Futrell JH. Int J Mass Spectrom Ion Phys 1970;4:165. Herod AA, Harrison AG. Int J Mass Spectrom Ion Phys 1970;4:415. McIver RT, Dunbar RC. Int J Mass Spectrom Ion Phys 1971;7:471.
[16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
S177
Anicich VG, Bowers MT. Int J Mass Spectrom Ion Phys 1973;11:329. Michalak L, Adamczyk B. Int J Mass Spectrom Ion Processes 1988;85:319. Field FH, Lampe FW. J Am Chem Soc 1958;80:5583. Bennett SL, Field FH. J Am Chem Soc 1972;94:6305. Huntress Jr WT, Pinizzotto Jr RF, Laudenslager JB. J Am Chem Soc 1973;95:4107. Wo´jcik L, Bederski K. Int J Mass Spectrom Ion Processes 1993;127:11. 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 Processes 1996;153:139.