- Email: [email protected]
Ionization of ammonia by electron impact at 25–1000eV
171
International Journal of Mass Spcctrometry and Ion Physics, 35 (1980) 171-178 @ Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
IONIZATION
K. BEDERSKI,
OF AMMONIA
L. WdJCIK
Institute of Physics, (Received
BY ELECTRON
IMPACT
eV
and B. ADAMCZYK
Uniuersity of Murie Curie-Skiodowsha,
19 December
AT 25-1000
Lublin (Poland)
1979)
ABSTRACT The results of the measurements of total and partial cross-sections for the ionization of ammonia by electron impact at 25-1000 eV are presented. The ion currents of NH;, NH;, NH*, N+, Hz, II* and NH:+ arc recorded_ The results are normalized to the absolute total cross-sections reported by Jain and Khare [ 10 J, and compared with values of the cross-sections reported in the litwature.
Partial ionization cross-section measurements were started by Bleakney [I,21 in 1929, who examined neon and argon ionization, with a Wien ionvelocity filter. Simultaneously with the development of mass spectrometry and progress in plasma physics and astrophysics, investigations in this field improved and were carried out by advancing techniques. However, since spectrometers and analyzers, even those of the highest standard, are subject to discrimination effects, the results obtained by different systems show considerable discrepancy_ The main factors responsible for discrimination effects are secondary electron emission and secondary ionization in the itin source, variation in the transmission of analyzing systems, secondary effects in detection systems, and variation in sensitivity of the systems depending on the kind of ions. In cycloidal mass spectrometry, as used in this work 13-71, these effects were considerably reduced. The use of the mass spectrometer generally yields relative values of partial cross-sections. This is caused by the fact that in the ion source the length of the ionization path and the concentration of atoms, or of gas molecules, are unknown. The absolute vahdes of partial cross-sections are obtained by comparison of the relative values of the cross-sections with the absolute total values found by other methods. EXPERIMENTAL
by
Cross-sections for the ionization of ammonia by electrons were measured means of a cycloidal mass spectrometer constructed by the authors
172
[ 3-71. The gas from the inlet system, in which the pressure was about 40 torr, was introduced by a needle valve and a capillary into a non-slit ion source [5,6]. The ions were produced by electrons of 25-1000 eV. The intensity of the electron current was 10 ,uA. Special attention was paid to the elimination of secondary effects in the ion source and to making the electron beam monoenergetic [ 53. Ion separation took place in the crossed homogeneous electric and magnetic fields. Extra focussing of the ion beam was used to increase the transmission coefficient between the ion source and the collector. The effect was achieved by use of an inhomogencous electric field in the vicinity of the ion source and of the collector 143. The currents produced by the separated ions were measured by a Faraday cup. The mass spectrometer was equipped with an automatic system for locating ion beams on the collector [7], which considerably shortened the measurement time. Prior to starting appropriate measurements, the working conditions of the spectrometer were so established as to ensure single-electron impact with a molecule, and thus a proportional correlation between the ion current and the electron current. The intensity of the analyzing electric fields was adjusted in order to have a plateau of the ion currents. RESULTS
AND
DISCUSSION
Total ionization
cross-sections
Absolute ionization cross-sections of NIIJ by electron impact, as obiaincd by several authors, are given in Fig. 1. The values of the absolute total cross-sections calculated by Gomet [8,9] differ from those found by other authors. His procedure for measurement of the absolute values of cross-sections is described in rcfs. 8 and 9. Jain and Kharc’s [lo] semi-empirical absolute cross-sections are based on the experimental data of Opal et al. [ 111. The results obtained by Crowe and McConkey 1123 are in good agreement with those presented here. This is, of course, a result of the normalizing procedure. Slightly lower values of absolute total ionization cross-sections reported by Mtik et al. [ 131 were normalized to t.he values obtained by Rapp and Englander-Golden [ 141 for argon. Total cross-sections for only one value of electron energy were reported by De Maria et al. [153 for 70 eV, Djuric-Prcger et al. [IS] and Lampe et al. 1171 for 75 eV, and Melton 1181 for 100 eV. Partial ionization
cross-sections
Partial ionization cross-sections are shown in Fig. 2.
of NH3 by electron
impact
at 25-1000
eV
173
NH3 ;;Es.o 0
I t
v Djuric-Preyer et al. - De Mcria et al. 0 Lampe et al ---Comet Mijrk et al. -..- Jaln,Khore - -- Crowe,Mc Conkey P Melton Author’s
o
NH;
-
NH;
=
0,8
0
NH+
x
3
-fl+
~8
_b
0
200
100 Electron
energy
300
0
200
[ eV]
400 Electron
800
600
qcuo
energy[eV]
Fig. 1 (left). Absolute total ionization cross-sections of NH3 by electron impact. Fig. 2 (right). Cross-sections for production from NH3 by electron impact.
of NH;,
NII;,
NH+, N+, Hi, I-I; and NHs+
The results are compared with those reported by Gomct [8,9], McConkey [ 121, Mtik et al. [ 131, and Melton [IS] in Figs. 3----g. NH;
Crowe and
partial cross-section
The results for NH; ions are in agreement with those obtained by Mtik [ 191 and Mjirk and Egger 1201, who used a double-focussing mass spectrometer, a Varian MAT CH5, for electron energies up to 180 eV (Fig. 3). Absolute values of the partial ionization cross-section of ammonia presented by M%rk [19] and Mtik and Egger [20] were obtained by normalization of the currents of Ar’ and ArZ+ to absolute values of the total crosssection for argon, reported by Rapp and Englander-Golden [ 14]_ Slight discrepancies are to be imputed to the normalizing procedure. The sum of the cross-sections reported by M&-k [19] and Mtik and Egger [20] lies below the curve of the total cross-section reported by Jain and Khare [ 101 (see Fig. 2). Above an electron energy of 150 eV, the values of the cross-sections obtained by Jain and Khare [lo] decrease more rapidly than those found in the present work. The curves reported by MZrk 1191 and MZrk and Eggcr [ZO] for NH;, NH’, HG and NH%+ (see Figs. 4, 5, 7, 9) have a similar tendency.
-.- Gmet ---
Crowe.Mc Conky et al. p Melton
-M&k
NH; *N---L-
-
Author’s
L_
.’
\
-.
./
-.
--
/
/’ /’ I
r j.---_,
r! I!
-_ - --__
---==z
0
:.
I
I I
,‘.___._. 0
300
100
Eleckon
Fig. 3. Compzu-ison impnct.
energy
reVI
of the cross-sections
for the production
of NH:
from
NII3
by electron
Crowe and McConkey [21] measured cross-sections by means of a quadrupole mass sg;eca:ometer for electron energies up to 300 eV. For NH*, the values of thz cross-sections reported by Crowe and McConkey are higher than those obtained in the present work. The reason is that the normalizing procedure of Jain and Khare [lo] took into consideration only NHf and NH; ions. In the opinion of the present authors, disregarding the other ions leads to an increase in the results of about 10%. The values of the cross-sections found by Gomet [S] for NH:, by use of a linear radio-frequency mass spectrometer, differ considerably from the rest. The shape of the curve is different. The reason for this disagreement is discussed in refs. 12 and 13. The cross-section found by Melton and co-workers 1223 for a single energy of 100 eV, by means of a mass spectrometer with a 60” magnetic field, lies below the value of the cross-section reported by MzXrk [19] and MZrk and Egger 1201 for the same energy value. The maxima of the curves presented are within the limits of electron energies between 65 and 76.5 eV, except for the curve measured by Gomet which has a maximum at an energy of 150 eV. NG partial cross-section The cross-sections obtained for the fra&nents of NH; by various authors arc given in Fig. 4.
175
-.- Gomet -- -
Crowe.Mc Conkey M&k et al. d Melton --Author’s
--
NH;
I
7cJl~
0
Electron Fig. 4. Comparison.
300
energy [eVJ
of the cross-sections
for the production
impact.
of NH;
from NH3 by electron
The maxima for the cross-sections are found to be within the energy limits of 75 and 86 eV. Only Gomct’s curve has its maximum at 125 eV. Such a shift may be caused by apparatus effects. However, the absence of a detailed description of the apparatus makes the discussion invalid. The cause may be the appearance of 0’ ions in the NH; beam.
NH+ -
0.3 -
“EY u b
/
/--
:
I I
\
Gomet ---Cmwe,Mc Conkey --M&k et al. 8 Melton ;+ Authorx
---
\
\
\
\
\
\
. __
ELectron energy Fig. 5. Comparison impact.
[ eV ]
of the cross-sections
for the production
of NH+ from
NH3
by electron
176
The steeper decrease in the curve obtained by Crowe and McConkey 1123 for higher energies is to be explained by their disregard of minority ions in the normalization procedure.
NH’ partial cross-section For NH* ions considerable discrepancies between the cross-sections reported by various authors are observed in the values and the shapes of the curves present (Fig. 5). High values of cross-sections, reported by Crowe and McConkey [ 123, are explained by these authors by the occurrence of dissociation effects in the vicinity of the cathode and by the kinetic energies of NH’ liberated in the process of dissociative ionization. In the case of NH*, N’, H; and H ions (Figs. 5--8), the curves measured by Gomet differ considerably in shape from those reported by other authors. It seems that the discrepancies may be explained by high kinetic energies of the ions. Cross-sections for NH’ ions at 100 eV reported by Melton end the present authors are in good agreement.
Other partial cross-sections Considerable discrepancies are also observed in the case of the results for N’, I& II* and NH:+ (Figs. 6-9). 1.5 -
_.- Gonlet
.!-r
i
A Melton
N+
z
;$,,o$a’.
:
E
0 0 b ym .-
i
-
i
i
Fig.
6 (left).
Fig.
7 (right).
Comparison
tron impact.
Comparison
electron impact.
of
the crosssections
Mdrk et al. Author-s
i
100
__L--.__-
Electron
qnergy [ eVJ of the c.vx.s-sections
Gomct
\\
1. Electron
-
-
P_I g 0
.-
H:
i
for the production
of NW from
for the production
of
200
energy
Ii;
300 [eV]
NH3
from
by eke-
NH3
by
177 --Gomer .-- Mcirk et II d Melton *---Author’s
H+
t
NH;+ -M&-II =
Electron
Fig. 8 (left). tron impact.
energy
Comparison
Electron
[eV]
of the cross-sections
Fig. 9 (right)_ Comparison electron impact.
for the production
of the cross-sections
energy
[ eV ]
of H+ from
for the production
et al
Author’s
of NHs+
NH3
by elec-
from
NH3
by
Apart from the authors mentioned so far, ionization cross-sections at an electron energy of 100 eV were reported by Mann et al. [23]- Since they presented their results as relative values, they are disregarded here when making comparison of the curves. A comparison of the ratio of the ion currents obtained by various authors for an energy of 100 eV is given in Table 1.
TABLE
1
Relative intensities of NH:, the incident electron energy Authors
iMann et al. [ 231 Gomet [ 8.91 Melton [ 18 ] Crowe and McConkey M&k et al. [ 133 Present work
[ 121
NH’, N+, Hz, of 100 cV
I~+ and NH;+
measured
by different
authors
NH;
NH+
N+
H;
H+
NH;+
NH:
NHZ,+
NH:
NH:
NH;
NH:
0.78 0.44 0.80 0.79
0.045 0.092 0.090 0.24
0.017 0.016 0.030
0.0002 0.0019 0.026
0.005 0.088 0.026
0.0002
0.80 0.90
0.030 0.086
0.011 0.039
0.0019 0.0021
0.011 0.066
0.0013 0.00084
at
178 CONCLUSIONS
The above comparison of the ionization cross-sections of ammonia by electron impact sometimes shows considerable discrepancies, as reported by various authors. The discrepancies are especially marked for ions with initial kinetic energy, as a result of dissociation of the molecules. These discrepancies are also due to some effects in the instruments used, as mentioned at the beginning of the paper. Another reason is the use of various normalization procedures for total ionization cross-sections. We suggest the necessity of further measurements of this type, which would probably result in a smaller dispersion of the values of a cross-section as’s function of electron energy. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
W. Bleakney, Phys. Rev., 34 (1929) 157. W. Bleakney, Phys. Rev., 36 (1930) 1303. B. Adamczyk, Ann. Univ. Marie Curie-Skfodowska, Sect. AA, 20 (1969/70) 141. B. Adamczyk, L. Wojcik, K. Bederski and M. Plcszcxybski, Ann. Univ. Marie CurieSklodowska, Sect. AA, 30 (1973) 369. B. Adamczyk, A.J.H. Boerboom and M. Lukasiewicz, Int. J. Mass Spectron. Ion Phys., 9 (1972) 407. B. Adamczyk, K. Bederski, W. Szyszko and L. Wojcik, Folia Sot. Sci. Lubl., 18 (1974) 167. L. Wojcik and B. Adamczyk, Folia Sot. Sci. Lubl., Cl8 (1974) 181. J.C. Gomet, Methodes Phys. An& 3 (1969) 269. J.C. Gomet, CR. Acad. Sci., Ser. B, 281 (1975) 627. D.K. Jain and S.P. Khare, J. Phys. B, 9 (1576) 1429. C.B. Opal, EC. Beaty and W.K. Peterson, At. Data, 4 (1972) 209. A. Crowe and J.W. McConkey, Int. J. Mass Spcctrom. Ion Phys., 24 (1977) 181. T.D. M%irk, F. Egger and M. Cheret, J. Chem. Phys., 67 (1977) 3795. D. Rapp and P. Englander-Golden, J. Chem. Phys., 43 (1965) 1464. G. De Maria, L. Malaspina and V. Piacente, Ric. Sci., Parte 2, Sez. A, 3 (1563) 681. N. Djuric-Prcger, D. Belie and M. Kurepa, i’roc. VIIIth Symp. Phys. Ionized Gases, Dubrovnik, 1976, p. 54. F.W. Lampe, J.C. Franklin and F.H. Field, J. Am. Chem. Sot., 79 (1957) 6129. L.E. Melton, J. Chem. Phys., 45 (3966)4414. T.D. Mlrk, J. Chem. Phys., 63 (1975) 3731. T.D. MHrk and F. Egger, Int. J. Mass Spectrom. Ion Pi~ys., 20 (1976) 89. A. Crowe and J.W. McConkey, J. Phys. B, 6 (1973) 2088. T.W. Martin, R.E. Rummel and C.E. Melton, Science, 138 (1962) 77. M.M. Mann, A. Hustrulid and J.T. Tatc, Phys. Rev., 58 (1940) 340.
International Journal of Mass Spcctrometry and Ion Physics, 35 (1980) 171-178 @ Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
IONIZATION
K. BEDERSKI,
OF AMMONIA
L. WdJCIK
Institute of Physics, (Received
BY ELECTRON
IMPACT
eV
and B. ADAMCZYK
Uniuersity of Murie Curie-Skiodowsha,
19 December
AT 25-1000
Lublin (Poland)
1979)
ABSTRACT The results of the measurements of total and partial cross-sections for the ionization of ammonia by electron impact at 25-1000 eV are presented. The ion currents of NH;, NH;, NH*, N+, Hz, II* and NH:+ arc recorded_ The results are normalized to the absolute total cross-sections reported by Jain and Khare [ 10 J, and compared with values of the cross-sections reported in the litwature.
Partial ionization cross-section measurements were started by Bleakney [I,21 in 1929, who examined neon and argon ionization, with a Wien ionvelocity filter. Simultaneously with the development of mass spectrometry and progress in plasma physics and astrophysics, investigations in this field improved and were carried out by advancing techniques. However, since spectrometers and analyzers, even those of the highest standard, are subject to discrimination effects, the results obtained by different systems show considerable discrepancy_ The main factors responsible for discrimination effects are secondary electron emission and secondary ionization in the itin source, variation in the transmission of analyzing systems, secondary effects in detection systems, and variation in sensitivity of the systems depending on the kind of ions. In cycloidal mass spectrometry, as used in this work 13-71, these effects were considerably reduced. The use of the mass spectrometer generally yields relative values of partial cross-sections. This is caused by the fact that in the ion source the length of the ionization path and the concentration of atoms, or of gas molecules, are unknown. The absolute vahdes of partial cross-sections are obtained by comparison of the relative values of the cross-sections with the absolute total values found by other methods. EXPERIMENTAL
by
Cross-sections for the ionization of ammonia by electrons were measured means of a cycloidal mass spectrometer constructed by the authors
172
[ 3-71. The gas from the inlet system, in which the pressure was about 40 torr, was introduced by a needle valve and a capillary into a non-slit ion source [5,6]. The ions were produced by electrons of 25-1000 eV. The intensity of the electron current was 10 ,uA. Special attention was paid to the elimination of secondary effects in the ion source and to making the electron beam monoenergetic [ 53. Ion separation took place in the crossed homogeneous electric and magnetic fields. Extra focussing of the ion beam was used to increase the transmission coefficient between the ion source and the collector. The effect was achieved by use of an inhomogencous electric field in the vicinity of the ion source and of the collector 143. The currents produced by the separated ions were measured by a Faraday cup. The mass spectrometer was equipped with an automatic system for locating ion beams on the collector [7], which considerably shortened the measurement time. Prior to starting appropriate measurements, the working conditions of the spectrometer were so established as to ensure single-electron impact with a molecule, and thus a proportional correlation between the ion current and the electron current. The intensity of the analyzing electric fields was adjusted in order to have a plateau of the ion currents. RESULTS
AND
DISCUSSION
Total ionization
cross-sections
Absolute ionization cross-sections of NIIJ by electron impact, as obiaincd by several authors, are given in Fig. 1. The values of the absolute total cross-sections calculated by Gomet [8,9] differ from those found by other authors. His procedure for measurement of the absolute values of cross-sections is described in rcfs. 8 and 9. Jain and Kharc’s [lo] semi-empirical absolute cross-sections are based on the experimental data of Opal et al. [ 111. The results obtained by Crowe and McConkey 1123 are in good agreement with those presented here. This is, of course, a result of the normalizing procedure. Slightly lower values of absolute total ionization cross-sections reported by Mtik et al. [ 131 were normalized to t.he values obtained by Rapp and Englander-Golden [ 141 for argon. Total cross-sections for only one value of electron energy were reported by De Maria et al. [153 for 70 eV, Djuric-Prcger et al. [IS] and Lampe et al. 1171 for 75 eV, and Melton 1181 for 100 eV. Partial ionization
cross-sections
Partial ionization cross-sections are shown in Fig. 2.
of NH3 by electron
impact
at 25-1000
eV
173
NH3 ;;Es.o 0
I t
v Djuric-Preyer et al. - De Mcria et al. 0 Lampe et al ---Comet Mijrk et al. -..- Jaln,Khore - -- Crowe,Mc Conkey P Melton Author’s
o
NH;
-
NH;
=
0,8
0
NH+
x
3
-fl+
~8
_b
0
200
100 Electron
energy
300
0
200
[ eV]
400 Electron
800
600
qcuo
energy[eV]
Fig. 1 (left). Absolute total ionization cross-sections of NH3 by electron impact. Fig. 2 (right). Cross-sections for production from NH3 by electron impact.
of NH;,
NII;,
NH+, N+, Hi, I-I; and NHs+
The results are compared with those reported by Gomct [8,9], McConkey [ 121, Mtik et al. [ 131, and Melton [IS] in Figs. 3----g. NH;
Crowe and
partial cross-section
The results for NH; ions are in agreement with those obtained by Mtik [ 191 and Mjirk and Egger 1201, who used a double-focussing mass spectrometer, a Varian MAT CH5, for electron energies up to 180 eV (Fig. 3). Absolute values of the partial ionization cross-section of ammonia presented by M%rk [19] and Mtik and Egger [20] were obtained by normalization of the currents of Ar’ and ArZ+ to absolute values of the total crosssection for argon, reported by Rapp and Englander-Golden [ 14]_ Slight discrepancies are to be imputed to the normalizing procedure. The sum of the cross-sections reported by M&-k [19] and Mtik and Egger [20] lies below the curve of the total cross-section reported by Jain and Khare [ 101 (see Fig. 2). Above an electron energy of 150 eV, the values of the cross-sections obtained by Jain and Khare [lo] decrease more rapidly than those found in the present work. The curves reported by MZrk 1191 and MZrk and Eggcr [ZO] for NH;, NH’, HG and NH%+ (see Figs. 4, 5, 7, 9) have a similar tendency.
-.- Gmet ---
Crowe.Mc Conky et al. p Melton
-M&k
NH; *N---L-
-
Author’s
L_
.’
\
-.
./
-.
--
/
/’ /’ I
r j.---_,
r! I!
-_ - --__
---==z
0
:.
I
I I
,‘.___._. 0
300
100
Eleckon
Fig. 3. Compzu-ison impnct.
energy
reVI
of the cross-sections
for the production
of NH:
from
NII3
by electron
Crowe and McConkey [21] measured cross-sections by means of a quadrupole mass sg;eca:ometer for electron energies up to 300 eV. For NH*, the values of thz cross-sections reported by Crowe and McConkey are higher than those obtained in the present work. The reason is that the normalizing procedure of Jain and Khare [lo] took into consideration only NHf and NH; ions. In the opinion of the present authors, disregarding the other ions leads to an increase in the results of about 10%. The values of the cross-sections found by Gomet [S] for NH:, by use of a linear radio-frequency mass spectrometer, differ considerably from the rest. The shape of the curve is different. The reason for this disagreement is discussed in refs. 12 and 13. The cross-section found by Melton and co-workers 1223 for a single energy of 100 eV, by means of a mass spectrometer with a 60” magnetic field, lies below the value of the cross-section reported by MzXrk [19] and MZrk and Egger 1201 for the same energy value. The maxima of the curves presented are within the limits of electron energies between 65 and 76.5 eV, except for the curve measured by Gomet which has a maximum at an energy of 150 eV. NG partial cross-section The cross-sections obtained for the fra&nents of NH; by various authors arc given in Fig. 4.
175
-.- Gomet -- -
Crowe.Mc Conkey M&k et al. d Melton --Author’s
--
NH;
I
7cJl~
0
Electron Fig. 4. Comparison.
300
energy [eVJ
of the cross-sections
for the production
impact.
of NH;
from NH3 by electron
The maxima for the cross-sections are found to be within the energy limits of 75 and 86 eV. Only Gomct’s curve has its maximum at 125 eV. Such a shift may be caused by apparatus effects. However, the absence of a detailed description of the apparatus makes the discussion invalid. The cause may be the appearance of 0’ ions in the NH; beam.
NH+ -
0.3 -
“EY u b
/
/--
:
I I
\
Gomet ---Cmwe,Mc Conkey --M&k et al. 8 Melton ;+ Authorx
---
\
\
\
\
\
\
. __
ELectron energy Fig. 5. Comparison impact.
[ eV ]
of the cross-sections
for the production
of NH+ from
NH3
by electron
176
The steeper decrease in the curve obtained by Crowe and McConkey 1123 for higher energies is to be explained by their disregard of minority ions in the normalization procedure.
NH’ partial cross-section For NH* ions considerable discrepancies between the cross-sections reported by various authors are observed in the values and the shapes of the curves present (Fig. 5). High values of cross-sections, reported by Crowe and McConkey [ 123, are explained by these authors by the occurrence of dissociation effects in the vicinity of the cathode and by the kinetic energies of NH’ liberated in the process of dissociative ionization. In the case of NH*, N’, H; and H ions (Figs. 5--8), the curves measured by Gomet differ considerably in shape from those reported by other authors. It seems that the discrepancies may be explained by high kinetic energies of the ions. Cross-sections for NH’ ions at 100 eV reported by Melton end the present authors are in good agreement.
Other partial cross-sections Considerable discrepancies are also observed in the case of the results for N’, I& II* and NH:+ (Figs. 6-9). 1.5 -
_.- Gonlet
.!-r
i
A Melton
N+
z
;$,,o$a’.
:
E
0 0 b ym .-
i
-
i
i
Fig.
6 (left).
Fig.
7 (right).
Comparison
tron impact.
Comparison
electron impact.
of
the crosssections
Mdrk et al. Author-s
i
100
__L--.__-
Electron
qnergy [ eVJ of the c.vx.s-sections
Gomct
\\
1. Electron
-
-
P_I g 0
.-
H:
i
for the production
of NW from
for the production
of
200
energy
Ii;
300 [eV]
NH3
from
by eke-
NH3
by
177 --Gomer .-- Mcirk et II d Melton *---Author’s
H+
t
NH;+ -M&-II =
Electron
Fig. 8 (left). tron impact.
energy
Comparison
Electron
[eV]
of the cross-sections
Fig. 9 (right)_ Comparison electron impact.
for the production
of the cross-sections
energy
[ eV ]
of H+ from
for the production
et al
Author’s
of NHs+
NH3
by elec-
from
NH3
by
Apart from the authors mentioned so far, ionization cross-sections at an electron energy of 100 eV were reported by Mann et al. [23]- Since they presented their results as relative values, they are disregarded here when making comparison of the curves. A comparison of the ratio of the ion currents obtained by various authors for an energy of 100 eV is given in Table 1.
TABLE
1
Relative intensities of NH:, the incident electron energy Authors
iMann et al. [ 231 Gomet [ 8.91 Melton [ 18 ] Crowe and McConkey M&k et al. [ 133 Present work
[ 121
NH’, N+, Hz, of 100 cV
I~+ and NH;+
measured
by different
authors
NH;
NH+
N+
H;
H+
NH;+
NH:
NHZ,+
NH:
NH:
NH;
NH:
0.78 0.44 0.80 0.79
0.045 0.092 0.090 0.24
0.017 0.016 0.030
0.0002 0.0019 0.026
0.005 0.088 0.026
0.0002
0.80 0.90
0.030 0.086
0.011 0.039
0.0019 0.0021
0.011 0.066
0.0013 0.00084
at
178 CONCLUSIONS
The above comparison of the ionization cross-sections of ammonia by electron impact sometimes shows considerable discrepancies, as reported by various authors. The discrepancies are especially marked for ions with initial kinetic energy, as a result of dissociation of the molecules. These discrepancies are also due to some effects in the instruments used, as mentioned at the beginning of the paper. Another reason is the use of various normalization procedures for total ionization cross-sections. We suggest the necessity of further measurements of this type, which would probably result in a smaller dispersion of the values of a cross-section as’s function of electron energy. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
W. Bleakney, Phys. Rev., 34 (1929) 157. W. Bleakney, Phys. Rev., 36 (1930) 1303. B. Adamczyk, Ann. Univ. Marie Curie-Skfodowska, Sect. AA, 20 (1969/70) 141. B. Adamczyk, L. Wojcik, K. Bederski and M. Plcszcxybski, Ann. Univ. Marie CurieSklodowska, Sect. AA, 30 (1973) 369. B. Adamczyk, A.J.H. Boerboom and M. Lukasiewicz, Int. J. Mass Spectron. Ion Phys., 9 (1972) 407. B. Adamczyk, K. Bederski, W. Szyszko and L. Wojcik, Folia Sot. Sci. Lubl., 18 (1974) 167. L. Wojcik and B. Adamczyk, Folia Sot. Sci. Lubl., Cl8 (1974) 181. J.C. Gomet, Methodes Phys. An& 3 (1969) 269. J.C. Gomet, CR. Acad. Sci., Ser. B, 281 (1975) 627. D.K. Jain and S.P. Khare, J. Phys. B, 9 (1576) 1429. C.B. Opal, EC. Beaty and W.K. Peterson, At. Data, 4 (1972) 209. A. Crowe and J.W. McConkey, Int. J. Mass Spcctrom. Ion Phys., 24 (1977) 181. T.D. M%irk, F. Egger and M. Cheret, J. Chem. Phys., 67 (1977) 3795. D. Rapp and P. Englander-Golden, J. Chem. Phys., 43 (1965) 1464. G. De Maria, L. Malaspina and V. Piacente, Ric. Sci., Parte 2, Sez. A, 3 (1563) 681. N. Djuric-Prcger, D. Belie and M. Kurepa, i’roc. VIIIth Symp. Phys. Ionized Gases, Dubrovnik, 1976, p. 54. F.W. Lampe, J.C. Franklin and F.H. Field, J. Am. Chem. Sot., 79 (1957) 6129. L.E. Melton, J. Chem. Phys., 45 (3966)4414. T.D. Mlrk, J. Chem. Phys., 63 (1975) 3731. T.D. MHrk and F. Egger, Int. J. Mass Spectrom. Ion Pi~ys., 20 (1976) 89. A. Crowe and J.W. McConkey, J. Phys. B, 6 (1973) 2088. T.W. Martin, R.E. Rummel and C.E. Melton, Science, 138 (1962) 77. M.M. Mann, A. Hustrulid and J.T. Tatc, Phys. Rev., 58 (1940) 340.