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Associative ionization of Ti, Zr, Gd, and Thin collisions with O and O2
..
Volume 29, number 1
:
CHEhiICAL PHYSICS LETTERS
ASSOCIATIVE
IONIZATION
IN COLLISIONS
I November 1974
OF Ti, Zr, Mg AND Th
WITH O.AND.0,
H.H. LO and W.L. FITE Expanuclear Laboratories, Inc., Pittsburgh, Pehsylvania 15238, USA
Received 24 June 19’74
Associative ionization a crossed beam technique.
cross sections for Ti, Zr, Gd, and Th with 0 and for Th with 02 have been measurei using Known associative ionization cross sections for U 6 0 and U f 02 were used for nomali-
zation of results.
The associative
ionization
used were mutually perpendicular. The metal atom source was a horizontally mounted tungsten tube made’by rolling fire layers of 0.001 in. tungsten foil. This source was loaded with two metals, the metal M under study and U, so that the metal atom beam consisted of two metals, in amounts depending on their vapor pressures and the temperature of the source. The normal operzting temperature of the metal atom source was about 2200 K. Following the measurement of the Ti + 0 cross section it was used as a secondary standard for measurements on Cd f 0. The details of the oxygen beam source have been described elsewhere [2]. While the oxygen,beam source was normally maintained at about 2200 K, it
processes
M’+O+=MO’+e
(1)
and M+02-,MO;+e have been studied for several species [l-4]. f’ective (ekperiiiental) associative icnization tions for U+O+UO+te
0) The efcross sec-
(3)
and U+02+UOZf+e
(4)
have recently been measured by Fite et al. [2] to be (1.62+0.41)X 1@-15cm’and(1.68~0.27)X lo-l7 cm2, respectively. We have examined the associative ionization cross, sections for Ti, Zr, Gd, and Th with atomic and molecular oxygen, utilizing associative ionization cross sections for processes (3) and (4) as primary standards. The present experiment is shoivn schematically in fig. 1. The electron, oxygenrand metal atom I beams
MOSS
Vacuum’
Elcctran Beam Met01Atom Beam
research was sponsored by the Defense Nuclear Agency under Subtask H1002 Work Unit No. 04, Contract No. F19628-72-C-0080. Cross sections for Thermal Reactions between Utanium Atoms and Atmospheric Species
*This
Melol
Furnace
: ‘. .’ ..‘.,
‘Fig. 1. ,Expe+nental
Atom
Sou,rce
xzrengement.
39
_
Voluyw 23; nuj@er’l
CHEMICAL F’HYSICS LEX’TERS
.’
1 Novet&er
1974
-
,was kept at rocm temperature’ when the reaction ‘, Th + g2 ~~‘l710~ + e was studied. The oxygen -beam was m~,dulated at 450 Hz by a tccthed.@sk. ‘, Ions produced ty the associative and electron im‘@A ion&at&s were nr/e selected by an Extrmuclear quadrupole niass filter tid detected,by a Bendix chan<rcn. ‘I& conventional phase sensitive tech.,nique.was used to handle ion signals related tc .he associative ionization reactions. Si&e both metals are simulkneously exposed to the same electron and oxygen beams, jn the,oame gel o+netry, the ratio of effective
associative
iotizaticn
C&S sections for processes (1) and (3) is given by
is the ratio of ion signals produced where S,o/SvO by’associative icniztition with 0 fcr, K anll U, $&/SL is the ratio bf ion signals created by eIectron impact upon the metal atoms;and &/Qb is the ratio of elec-trcn impact ionization cross sections for M and U. $nilarly, the ratio of effective ionization cross section for processes (2) and (4) can be expressed by
is the ratio of ion &gnals observed wheie S&JSuo, .due to assbcjative ionization of M utd U with 02. The experimental prccedurk was firs: to turn on .the lOOeV electron hem that ionizes the mixed metal beam..The observed ratio of icn’signals, CM/p”,
a.ldng with .Qir/Qb provides the.relative number densi-
tips ,of M ‘and U in the beam. With the electron beam turned off, the partially dissociated oxygen beam was intr’oduccd is cross the mixed metal beam. LMO+and Ub+ signals frc!n pro&es (1) tid (3) [or MO; and IJO; sign& from processes (2) and (4)] were observed. Putting observed da,ta’cf S&/S;,and Shlo/Suo (or S ,~o,/Su~,) in’ eq. (5) [& eq. (6)], the ratio cf’effective associative ionization cross sections, Qfi~o/Q~o (or Q&i&,), to the ratio of electron impact icnizaticn cross sections, Qb/Qb, was immediately cbtained. .T%e results are presented.in table 1. Of the four met& stuciied, only ThOz was seen in the prccess (2) tince ali olher reactions itith 0, are endothermic. The indicated error of each reaction is the standard deviation of at least 5 runs. In t!!e present them+ energy crossed beam experiments the effective cross sections, determined in terms cf.ta&ly observable experimental quantities, are averages over velocity distribut&s of two maxwellian beams. The true cross.sections can be deduced from an aalysis using formulas derived in the earlier paper [2]. In so doing, it is presumed that for asscciative ionization between the metals studied and oxygen atoms and mo!ecules the cross skcticns are independent of velocity. This independence has been exp&imentally established’for associative ionization between U and 02 [2]. ,Ratics of effective to true associative ionization cross sections for metals studied under different experimental conditions are shc!m.in table 2. The true associative ionization cross set tions with respect to the ratio of electron impact ionization cross sections for Ti, Zr, Gd, and ‘I’h with 0 and 0,
are tabulated in table 3: The rea&n’fcr not evaluating absolute cross sections is that ionization cross sections
1
Ratios of the &tive.effec.tivc
:
Qflro@'vo
M
Qj$Qb
ii
._”
Zr.
-
‘Gd ..
-.
l-3
associative ionization cross section to the-ratio of electron impact ionization cross sections
‘-.,
( 3.30~ 3.72)X 1O-2 ,..(87.2 213.8 )X,1O-2 '(66.0* 11.9 )X 1cf-2
Qho,~Qiro, Q;f/Qb
.(97.8 t 9.0) 7 10-z
QidQbo Qif/Q%i
16.6
l
-
1.0
a)
Volume &,number
CHEMICAL PH+CS
1
Table 2 khtir~i of effective to tr& associative i~~~~~i~~ cross settioris~~ Temperature of hi (K)
M
‘Ti
1800 2200. 2200 18110 2200 2200
Zr Cd Th’ ru
.-.
Qhioa)
Q&b)
Qnio
QMO~’
1.163
7. -
1.192
:
1.107 1.047 1.045 1.042
1.473 1.467
a) Oxygen beam source at 2200 R. b) Oxygen beam source at 300 K.
LETTE.RS
okelectron impact foi aii the metals studied.are not ykt &own. In co&Iusion, the cross skian for associative ionization of .O with Ti is about 20 times smalkr than that with Zr, Gd, and Th, assuming that electron impact ionization cross sections are ec+i for me& StUdied. &de? the same assumption, 23, Gd, and Th, seem, within experimental error, to have simiIar a-%0ciative ionizSon cross sections in collisions with 0. Ij is also interesting to note that the ratio of true cross sections for associative ionization of 0 and 02’ with This 69 t 25 3s.compar~d to IO? C 21 with U. The results on Th 3re in fair agreement with the con,cIusions of Zavitsanos [3]_ . Finally, upon repfacing oxygen by water VaFOL so & to produce a.beam containing OH radicais, we have confirmed the report of Cohen [4] &at t&e process Bai-OH+BaOH”ie
Tabie 3 True associa!ive ionization cross sections with revcct to the ratio of efectrcn impnct ionization cross sectionsa‘f &i*t@+i
ie”,>
Qzrol(Q$$Q”v Q~~~l~Q~~~Q~~ QlihoKQc,@“uI QTh~*~(Q~~/~~ a) EIection
energy
(4.53 (I.29 (8.35 (1.03 (I.@
rt 1.51) i 0.38) r 2.83) i 0.32) * 0.28)
= 100 eV. All cross sections
x lo-” x 10-1s x 10-16 X 1O-‘5 x lo-” are in cm2_
(71
proceeds with an apparently large cross section.
References [l] W.L. Fitc and.P. Irving, J. Chem. Phyr 56 (1972) 4227. [2] W.L. Fite, H.H. Lo and P.’ k&g. J. Chem. Phps. 60 (1974) 1236. [3] P.D.‘Zavitsanos, J. Chem. Phys. 59 (1973) 2162 [4] RB,Cohen, private communi~~on (1974).
..
Volume 29, number 1
:
CHEhiICAL PHYSICS LETTERS
ASSOCIATIVE
IONIZATION
IN COLLISIONS
I November 1974
OF Ti, Zr, Mg AND Th
WITH O.AND.0,
H.H. LO and W.L. FITE Expanuclear Laboratories, Inc., Pittsburgh, Pehsylvania 15238, USA
Received 24 June 19’74
Associative ionization a crossed beam technique.
cross sections for Ti, Zr, Gd, and Th with 0 and for Th with 02 have been measurei using Known associative ionization cross sections for U 6 0 and U f 02 were used for nomali-
zation of results.
The associative
ionization
used were mutually perpendicular. The metal atom source was a horizontally mounted tungsten tube made’by rolling fire layers of 0.001 in. tungsten foil. This source was loaded with two metals, the metal M under study and U, so that the metal atom beam consisted of two metals, in amounts depending on their vapor pressures and the temperature of the source. The normal operzting temperature of the metal atom source was about 2200 K. Following the measurement of the Ti + 0 cross section it was used as a secondary standard for measurements on Cd f 0. The details of the oxygen beam source have been described elsewhere [2]. While the oxygen,beam source was normally maintained at about 2200 K, it
processes
M’+O+=MO’+e
(1)
and M+02-,MO;+e have been studied for several species [l-4]. f’ective (ekperiiiental) associative icnization tions for U+O+UO+te
0) The efcross sec-
(3)
and U+02+UOZf+e
(4)
have recently been measured by Fite et al. [2] to be (1.62+0.41)X 1@-15cm’and(1.68~0.27)X lo-l7 cm2, respectively. We have examined the associative ionization cross, sections for Ti, Zr, Gd, and Th with atomic and molecular oxygen, utilizing associative ionization cross sections for processes (3) and (4) as primary standards. The present experiment is shoivn schematically in fig. 1. The electron, oxygenrand metal atom I beams
MOSS
Vacuum’
Elcctran Beam Met01Atom Beam
research was sponsored by the Defense Nuclear Agency under Subtask H1002 Work Unit No. 04, Contract No. F19628-72-C-0080. Cross sections for Thermal Reactions between Utanium Atoms and Atmospheric Species
*This
Melol
Furnace
: ‘. .’ ..‘.,
‘Fig. 1. ,Expe+nental
Atom
Sou,rce
xzrengement.
39
_
Voluyw 23; nuj@er’l
CHEMICAL F’HYSICS LEX’TERS
.’
1 Novet&er
1974
-
,was kept at rocm temperature’ when the reaction ‘, Th + g2 ~~‘l710~ + e was studied. The oxygen -beam was m~,dulated at 450 Hz by a tccthed.@sk. ‘, Ions produced ty the associative and electron im‘@A ion&at&s were nr/e selected by an Extrmuclear quadrupole niass filter tid detected,by a Bendix chan<rcn. ‘I& conventional phase sensitive tech.,nique.was used to handle ion signals related tc .he associative ionization reactions. Si&e both metals are simulkneously exposed to the same electron and oxygen beams, jn the,oame gel o+netry, the ratio of effective
associative
iotizaticn
C&S sections for processes (1) and (3) is given by
is the ratio of ion signals produced where S,o/SvO by’associative icniztition with 0 fcr, K anll U, $&/SL is the ratio bf ion signals created by eIectron impact upon the metal atoms;and &/Qb is the ratio of elec-trcn impact ionization cross sections for M and U. $nilarly, the ratio of effective ionization cross section for processes (2) and (4) can be expressed by
is the ratio of ion &gnals observed wheie S&JSuo, .due to assbcjative ionization of M utd U with 02. The experimental prccedurk was firs: to turn on .the lOOeV electron hem that ionizes the mixed metal beam..The observed ratio of icn’signals, CM/p”,
a.ldng with .Qir/Qb provides the.relative number densi-
tips ,of M ‘and U in the beam. With the electron beam turned off, the partially dissociated oxygen beam was intr’oduccd is cross the mixed metal beam. LMO+and Ub+ signals frc!n pro&es (1) tid (3) [or MO; and IJO; sign& from processes (2) and (4)] were observed. Putting observed da,ta’cf S&/S;,and Shlo/Suo (or S ,~o,/Su~,) in’ eq. (5) [& eq. (6)], the ratio cf’effective associative ionization cross sections, Qfi~o/Q~o (or Q&i&,), to the ratio of electron impact icnizaticn cross sections, Qb/Qb, was immediately cbtained. .T%e results are presented.in table 1. Of the four met& stuciied, only ThOz was seen in the prccess (2) tince ali olher reactions itith 0, are endothermic. The indicated error of each reaction is the standard deviation of at least 5 runs. In t!!e present them+ energy crossed beam experiments the effective cross sections, determined in terms cf.ta&ly observable experimental quantities, are averages over velocity distribut&s of two maxwellian beams. The true cross.sections can be deduced from an aalysis using formulas derived in the earlier paper [2]. In so doing, it is presumed that for asscciative ionization between the metals studied and oxygen atoms and mo!ecules the cross skcticns are independent of velocity. This independence has been exp&imentally established’for associative ionization between U and 02 [2]. ,Ratics of effective to true associative ionization cross sections for metals studied under different experimental conditions are shc!m.in table 2. The true associative ionization cross set tions with respect to the ratio of electron impact ionization cross sections for Ti, Zr, Gd, and ‘I’h with 0 and 0,
are tabulated in table 3: The rea&n’fcr not evaluating absolute cross sections is that ionization cross sections
1
Ratios of the &tive.effec.tivc
:
Qflro@'vo
M
Qj$Qb
ii
._”
Zr.
-
‘Gd ..
-.
l-3
associative ionization cross section to the-ratio of electron impact ionization cross sections
‘-.,
( 3.30~ 3.72)X 1O-2 ,..(87.2 213.8 )X,1O-2 '(66.0* 11.9 )X 1cf-2
Qho,~Qiro, Q;f/Qb
.(97.8 t 9.0) 7 10-z
QidQbo Qif/Q%i
16.6
l
-
1.0
a)
Volume &,number
CHEMICAL PH+CS
1
Table 2 khtir~i of effective to tr& associative i~~~~~i~~ cross settioris~~ Temperature of hi (K)
M
‘Ti
1800 2200. 2200 18110 2200 2200
Zr Cd Th’ ru
.-.
Qhioa)
Q&b)
Qnio
QMO~’
1.163
7. -
1.192
:
1.107 1.047 1.045 1.042
1.473 1.467
a) Oxygen beam source at 2200 R. b) Oxygen beam source at 300 K.
LETTE.RS
okelectron impact foi aii the metals studied.are not ykt &own. In co&Iusion, the cross skian for associative ionization of .O with Ti is about 20 times smalkr than that with Zr, Gd, and Th, assuming that electron impact ionization cross sections are ec+i for me& StUdied. &de? the same assumption, 23, Gd, and Th, seem, within experimental error, to have simiIar a-%0ciative ionizSon cross sections in collisions with 0. Ij is also interesting to note that the ratio of true cross sections for associative ionization of 0 and 02’ with This 69 t 25 3s.compar~d to IO? C 21 with U. The results on Th 3re in fair agreement with the con,cIusions of Zavitsanos [3]_ . Finally, upon repfacing oxygen by water VaFOL so & to produce a.beam containing OH radicais, we have confirmed the report of Cohen [4] &at t&e process Bai-OH+BaOH”ie
Tabie 3 True associa!ive ionization cross sections with revcct to the ratio of efectrcn impnct ionization cross sectionsa‘f &i*t@+i
ie”,>
Qzrol(Q$$Q”v Q~~~l~Q~~~Q~~ QlihoKQc,@“uI QTh~*~(Q~~/~~ a) EIection
energy
(4.53 (I.29 (8.35 (1.03 (I.@
rt 1.51) i 0.38) r 2.83) i 0.32) * 0.28)
= 100 eV. All cross sections
x lo-” x 10-1s x 10-16 X 1O-‘5 x lo-” are in cm2_
(71
proceeds with an apparently large cross section.
References [l] W.L. Fitc and.P. Irving, J. Chem. Phyr 56 (1972) 4227. [2] W.L. Fite, H.H. Lo and P.’ k&g. J. Chem. Phps. 60 (1974) 1236. [3] P.D.‘Zavitsanos, J. Chem. Phys. 59 (1973) 2162 [4] RB,Cohen, private communi~~on (1974).
..