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Unimolecular and collision induced dissociation of cluster ions
Journal of Mass Spectrometry and Ion Physics, 47 (1983) 195-198 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
International
UNIMOLECULAR K. STEPHAN Abt.
AND COLLISION
DISSOCIATION
OF CLUSTER
IONS
and T.D. M#RK
f. Kernphysik
Leopold
INDUCED
195
Franzens
Inst.
u. Gaselektronik, Universitgt,
A 6020
f. Experimentalphysik
Innsbruck
(Austria)
ABSTRACT Unimolecular and collision-induced dissociations of a number of atomic and molecular cluster ions, produced by electron impact ionization of neutral clusters, were investigated quantitatively using a double focussing reversed Results obtained are important for the detecsector type mass spectrometer. tion of clusters and for the development of appropriate theoretical fragmentation
models.
INDRODUCTION Properties ranging
from
expansion
mass
high
ionic
and/or
advantage degrees ties. cess
of mass
collision
of freedom, allows,
within State
metastable
and
have
(HBO),
ion clusters.
unimolecular clearly from
recently
distinguish
those
which
topic
Moreover,
the
size,
with
concerning
these
by decomposition
the
for
of unimole-
different
similar
into
of
importance
ions offers
having
but having insight
of clusters
investigation
ions
and rota-
by electron
combination
is of great
of molecular
the unique numbers
chemical
of
properpro-
fragmentation
of the quasi-equilibrium-theory. (ref.
l-3) were
of cluster reported
studies
of cluster
5-11).
cluster
decompose
0020-~331/83/000~0000/$03.00
the first
ions
Independently,
(ref.
interest
ion formation
This
further
in
is fragmentation
series
dissociation
impact
ionization
of cluster
and
probed
of methods,
Supersonic
of vibrationally
dissociation
dissociation
(ref.4)
or after
expansion.
are then
current
detection
spectra.
complexity
Shukla
or Penning
system.
in principle,
the frame
beams
induced
of generating
This
electron
process
by a variety
to nozzle
which
of particular
in the analyzing
interpretation
cular
investigated
to produce
molecules
cluster
of
ionization
species
used
A problem
techniques
are
spectrometry
photoionization
spectrometry.
in the
mass
generally
ionization,
either
clusters
Van der Waals
cooled
experimental
the
pressure
is e.g.
tionally impact
of gas phase
The
ions
investigated
in Ar,
important
ions which
0
on the unimolecular
we have
by metastable
to report
(CO, and acetone).
by
Sunner
and
of
Kebarle
dissociation
of K+.
the occurrence
N2, CO2 and NH3 produced
objective
decay
the observation
of our work
collision
dissociation,
induced
was
by
(1) to
dissociation
(2) to detect
1983 Elsevier ScientificPublishingCompany
of
experi-
196 mental
parameters
of metastable description
in cluster
cluster
production
ions and
of metastable
which
might
(3) to provide
cluster
influence
some guidance
the production
for the theoretical
ion decomposition.
EXPERIMENTAL The electron used
have
duced
been described
by expanding
be clustered stagnation
are extracted
tric
field
by cluster
to their
vestigation
of cluster
AND
ciation
occurring
slit,
to
The
- 105 K. The
at right angles
by electron
impact
regime
thus allowing
elec-
plates
to sweep
by
ioniza-
by a weak
deflection
serve
and background
double
corrobated
focussing
by decoupling method
in the
the ion
to distinguish
ions with
the same
mass
the direct free
accor-
deflection
analysis
region.
the reliability
dissociations and extended
spectrometer
the acceleration,
allows
in the field
we checked
the pressure
this
(see Fig. yields
whereas
be obtained
Applying
dependence
to distinguish
pressure
intercept), may
vestigated
to temperatures
Special
pro-
of the species
is crossed
spectrometer
are
of speci-
Prior
to the in-
of the apparatus
and
of NO2 and of propane
previous
(ref.
measurements.
DISCUSSION
to zero
'pressure
channels
ions,
(CID) dissociations
curves
clusters
a 10 urn nozzle.
ionization
chamber.
ionization
the metastable
obtained
it is possible
duced
the
entrance
15). This
processes
By measuring rate
(ref.
by studying
Results
RESULTS
from
in a reversed
dissociation field
fic dissociation
7,16).
He through
spectrometer
13,14),
and magnetic
technique
Neutral
Ions produced
and mass
spectrometer
Ions are analyzed ding
angles
and the mass
100 to 500 torr
clusters
into collision
the mass
12-14).
can be cooled
energy.
ion source
ions formed
(ref.
of
the neutral
at right
between
across
between
the nozzle
penetrating
ion optics
a mixture
beam of variable
tion
(ref.
source
1000 to 2000 Torr
beam containing
an electron
m/ze
with and
beam-ion
previously
typically
seeded chamber
molecular
beam
impact-molecular
from
technique
quantitatively
of the unimolecular
between
metastable
(M) and collision
1 as an example).
Extrapolation
the rate for metastable
the cross slope
section
the following
(zero-
induced
reactions
mechanism
were
is given
parenthesis): + H
(1)
NH3+ -f NH2+
(2)
(~~3)2+
+ NH~+
f NH~
(CID + M)
(3)
(NH&+
+ NH3+
+ NH3
(CID)
(4)
(NH3)2H'
-+ NH4+
(CID)
+ NH3
disso-
dependences.
unimolecular
dissociation
in-
of these
dissociation
for collision
of the respective
(the observed
decomposition
(CID)
inin
197
(NH3)2H+
+ + (NH3j3
(6)
(NH&H+
+
(NH4 +) + 2 NH3
(CID)
(7)
(NH3)3H+
+
(NH3)2H+
(CID + M)
(8)
(co*)*+
(9)
A$
+ co2+
ArN4+
(11)
+ N4'
Ar2N2+
(12)
ment
(20 to
over,
we have
found
that
tically
the fact,
the neutral of
to this model, sion
will
in
collision
induced.
for small
cluster
predissociation
(CID + M) energy
dependence
of reaction
regime
accessible
to our experi-
ratio
state
the dependence
process
distribution
(and nozzle)
on this
+
10%. More-
of the metastable
before
ionization
temperature.
cluster
temperature
This
(after
de-
(see also Ref.
studies
by a simple
pseudo-oscillator
of these
(3),
On the other
(4),
clusters
(6) and
for Ar3+, might
ArN2+ be
that
observed
and M4+.
invoked
small According
impact such
(8), are observed also
impact
model.
work
leads
4).
5-11)
by electron
Xn the. present
hand we have
tunneling
(ref.
is strongly in turn
electron
the present
dissociation.
ions, e.g.
within
gas temperature. It was +* -f Ar t changes dramarate for Ar3 2 (see Fig. 2). This is likely due to
in the ionic
from
prompt
does not change
of the stagnation
dissociation
states
and/or
the electron in the energy
investigated
the energization
result as e.g.
or colli-
simple
disso-
to be exclusively
metastable
In this
as a likely
case
decay (forbidden]
mechanism
of
metastability. The
(2) and energy tors
that
be described
ciations,
this
(CID + M)
+ ArN2
gas
depending
ions may
(CID + M)
gas temperature
It can be concluded cluster
(C.ID + M)
+ Ar
also
stagnation
also
(CID + M)
+ N2
ion current
by the stagnation
ionization)
(CID + M)
(CID + M)
the unimolecular
to a distribution
(CID + M)
+ Ar
studied
found
recently
that
(CID + M)
+ ArPj2+ + Ar
rate as a function
with
affected
have
we
It was
180 eV) the
composition
(CID)
N4+ + N2+ + N2
(13)
(lo).
+ NH3
f co2
+ ArN2+
In addition
+ NH2
-f Ar ' t Ar 2 + Ar + 2Ar + +N ArN2 +Ar 2 +N t Ar 2+
(10)
(9) and
(CID + PI)
(5)
observation (5) and
exchange
might
of metastable
the dissociation within
control
decay reaction
for the rearrangement (7) suggests
that
processes
in this case
a statistical
ensemble
of strongly-coupled
the decomposition
kinetics
of these
species
oscilla(QET theory).
198
Ion signal Of rmduct ion
t
M: H+(NH&-NHq++NH3 ClD:H+(NH3)2+X--NHq++NH3+X
Collision induced dissociation
Unimoleculer decay ( M) 2.5 Gas
pressure
5 in field free region
FIG ,1
z5.10 (Tom)
-5
>
100
I,
I50 I
,
Stagnation
I,
,
gas
,
,
,
200 ,
,
,
,
,
temperature('K)
FIG,~
REFERENCES
1
A.J. State and A.K. Shukla, Int. J. Mass Spectrom. Ion Phys., 36 (1980) 119 - 122 A.J. State and A.K. Shukta, Chem. Phys. Lett., 85 (1982) 157 - 160 A-J. State and A.K. Shukla, J. Phys. Chem., 86 (1982) 865 - 867 J. Sunner and P. Kebarle, J. Phys. Chem., 85 (1981) 327 - 335 J-H.. Futrell, K. Stephan, A.W. Castleman, Jr., and J.D. Mark, Proc. 8th Int. Symp. Molecular Beams, Cannes (19811 262 - 265 K. Stephan and T.D. Mgrk, Chem. Phys. Lett., 87 (1982) 226 - 228 6 J.H. Futrell, K. Stephan, and T.D. M;irk, J. Chem. Phys., June, 1982 7 K. Stephan, T.D. MBrk, J.H. Futrell and A.W. Castleman, Jr., Vacuum 8 TAIP, in print K. Stephan, T.D. mrk, E. MZrk, A. Stamatovic, N. Djuric, and A.W. 9 in print Castleman, Jr., Beitr. Plasmaphysik, 20 K. Stephan and T.D. MSrk, Chem. Phys. Lett., in print Futrell, E. fit-k, K.I. Peterson, 11 T-D_ M;irk, K. Stephan, H. Helm, J-H. N. Djuric and A. Stamatovic, SASP, 3(1982) 7 - 18 A.W. Castleman, Jr., 12 H. Helm, K. Stephan and T.D. M;irk, Phys. Rev., A 19 (1979) 2154 - 2160 K. Stephan, H. Helm and T.D. &r-k, J. Chem. Phys., 73 (1980) 3763 - 3778 1: H. Helm, K. Stephan, T.D. M;irk and D.L. Huestis, J. Chem.Phys., 74 (1981) 3844 - 3851 R.G. Cooks, J.H. Beynon, R.M. Caprioli, and G.R. Lester, Metastable 15 Ions (Elsevier, Amsterdam, 1973) E. M;irk, T.D. l%rk, Y.B. Kim and K. Stephan, J. Chem. Phys., 75 (1983) 16 4446 - 4453 Work supported by Usterr. Forschungsfonds under Projekt S-18/05 and S-18/08.
International
UNIMOLECULAR K. STEPHAN Abt.
AND COLLISION
DISSOCIATION
OF CLUSTER
IONS
and T.D. M#RK
f. Kernphysik
Leopold
INDUCED
195
Franzens
Inst.
u. Gaselektronik, Universitgt,
A 6020
f. Experimentalphysik
Innsbruck
(Austria)
ABSTRACT Unimolecular and collision-induced dissociations of a number of atomic and molecular cluster ions, produced by electron impact ionization of neutral clusters, were investigated quantitatively using a double focussing reversed Results obtained are important for the detecsector type mass spectrometer. tion of clusters and for the development of appropriate theoretical fragmentation
models.
INDRODUCTION Properties ranging
from
expansion
mass
high
ionic
and/or
advantage degrees ties. cess
of mass
collision
of freedom, allows,
within State
metastable
and
have
(HBO),
ion clusters.
unimolecular clearly from
recently
distinguish
those
which
topic
Moreover,
the
size,
with
concerning
these
by decomposition
the
for
of unimole-
different
similar
into
of
importance
ions offers
having
but having insight
of clusters
investigation
ions
and rota-
by electron
combination
is of great
of molecular
the unique numbers
chemical
of
properpro-
fragmentation
of the quasi-equilibrium-theory. (ref.
l-3) were
of cluster reported
studies
of cluster
5-11).
cluster
decompose
0020-~331/83/000~0000/$03.00
the first
ions
Independently,
(ref.
interest
ion formation
This
further
in
is fragmentation
series
dissociation
impact
ionization
of cluster
and
probed
of methods,
Supersonic
of vibrationally
dissociation
dissociation
(ref.4)
or after
expansion.
are then
current
detection
spectra.
complexity
Shukla
or Penning
system.
in principle,
the frame
beams
induced
of generating
This
electron
process
by a variety
to nozzle
which
of particular
in the analyzing
interpretation
cular
investigated
to produce
molecules
cluster
of
ionization
species
used
A problem
techniques
are
spectrometry
photoionization
spectrometry.
in the
mass
generally
ionization,
either
clusters
Van der Waals
cooled
experimental
the
pressure
is e.g.
tionally impact
of gas phase
The
ions
investigated
in Ar,
important
ions which
0
on the unimolecular
we have
by metastable
to report
(CO, and acetone).
by
Sunner
and
of
Kebarle
dissociation
of K+.
the occurrence
N2, CO2 and NH3 produced
objective
decay
the observation
of our work
collision
dissociation,
induced
was
by
(1) to
dissociation
(2) to detect
1983 Elsevier ScientificPublishingCompany
of
experi-
196 mental
parameters
of metastable description
in cluster
cluster
production
ions and
of metastable
which
might
(3) to provide
cluster
influence
some guidance
the production
for the theoretical
ion decomposition.
EXPERIMENTAL The electron used
have
duced
been described
by expanding
be clustered stagnation
are extracted
tric
field
by cluster
to their
vestigation
of cluster
AND
ciation
occurring
slit,
to
The
- 105 K. The
at right angles
by electron
impact
regime
thus allowing
elec-
plates
to sweep
by
ioniza-
by a weak
deflection
serve
and background
double
corrobated
focussing
by decoupling method
in the
the ion
to distinguish
ions with
the same
mass
the direct free
accor-
deflection
analysis
region.
the reliability
dissociations and extended
spectrometer
the acceleration,
allows
in the field
we checked
the pressure
this
(see Fig. yields
whereas
be obtained
Applying
dependence
to distinguish
pressure
intercept), may
vestigated
to temperatures
Special
pro-
of the species
is crossed
spectrometer
are
of speci-
Prior
to the in-
of the apparatus
and
of NO2 and of propane
previous
(ref.
measurements.
DISCUSSION
to zero
'pressure
channels
ions,
(CID) dissociations
curves
clusters
a 10 urn nozzle.
ionization
chamber.
ionization
the metastable
obtained
it is possible
duced
the
entrance
15). This
processes
By measuring rate
(ref.
by studying
Results
RESULTS
from
in a reversed
dissociation field
fic dissociation
7,16).
He through
spectrometer
13,14),
and magnetic
technique
Neutral
Ions produced
and mass
spectrometer
Ions are analyzed ding
angles
and the mass
100 to 500 torr
clusters
into collision
the mass
12-14).
can be cooled
energy.
ion source
ions formed
(ref.
of
the neutral
at right
between
across
between
the nozzle
penetrating
ion optics
a mixture
beam of variable
tion
(ref.
source
1000 to 2000 Torr
beam containing
an electron
m/ze
with and
beam-ion
previously
typically
seeded chamber
molecular
beam
impact-molecular
from
technique
quantitatively
of the unimolecular
between
metastable
(M) and collision
1 as an example).
Extrapolation
the rate for metastable
the cross slope
section
the following
(zero-
induced
reactions
mechanism
were
is given
parenthesis): + H
(1)
NH3+ -f NH2+
(2)
(~~3)2+
+ NH~+
f NH~
(CID + M)
(3)
(NH&+
+ NH3+
+ NH3
(CID)
(4)
(NH3)2H'
-+ NH4+
(CID)
+ NH3
disso-
dependences.
unimolecular
dissociation
in-
of these
dissociation
for collision
of the respective
(the observed
decomposition
(CID)
inin
197
(NH3)2H+
+ + (NH3j3
(6)
(NH&H+
+
(NH4 +) + 2 NH3
(CID)
(7)
(NH3)3H+
+
(NH3)2H+
(CID + M)
(8)
(co*)*+
(9)
A$
+ co2+
ArN4+
(11)
+ N4'
Ar2N2+
(12)
ment
(20 to
over,
we have
found
that
tically
the fact,
the neutral of
to this model, sion
will
in
collision
induced.
for small
cluster
predissociation
(CID + M) energy
dependence
of reaction
regime
accessible
to our experi-
ratio
state
the dependence
process
distribution
(and nozzle)
on this
+
10%. More-
of the metastable
before
ionization
temperature.
cluster
temperature
This
(after
de-
(see also Ref.
studies
by a simple
pseudo-oscillator
of these
(3),
On the other
(4),
clusters
(6) and
for Ar3+, might
ArN2+ be
that
observed
and M4+.
invoked
small According
impact such
(8), are observed also
impact
model.
work
leads
4).
5-11)
by electron
Xn the. present
hand we have
tunneling
(ref.
is strongly in turn
electron
the present
dissociation.
ions, e.g.
within
gas temperature. It was +* -f Ar t changes dramarate for Ar3 2 (see Fig. 2). This is likely due to
in the ionic
from
prompt
does not change
of the stagnation
dissociation
states
and/or
the electron in the energy
investigated
the energization
result as e.g.
or colli-
simple
disso-
to be exclusively
metastable
In this
as a likely
case
decay (forbidden]
mechanism
of
metastability. The
(2) and energy tors
that
be described
ciations,
this
(CID + M)
+ ArN2
gas
depending
ions may
(CID + M)
gas temperature
It can be concluded cluster
(C.ID + M)
+ Ar
also
stagnation
also
(CID + M)
+ N2
ion current
by the stagnation
ionization)
(CID + M)
(CID + M)
the unimolecular
to a distribution
(CID + M)
+ Ar
studied
found
recently
that
(CID + M)
+ ArPj2+ + Ar
rate as a function
with
affected
have
we
It was
180 eV) the
composition
(CID)
N4+ + N2+ + N2
(13)
(lo).
+ NH3
f co2
+ ArN2+
In addition
+ NH2
-f Ar ' t Ar 2 + Ar + 2Ar + +N ArN2 +Ar 2 +N t Ar 2+
(10)
(9) and
(CID + PI)
(5)
observation (5) and
exchange
might
of metastable
the dissociation within
control
decay reaction
for the rearrangement (7) suggests
that
processes
in this case
a statistical
ensemble
of strongly-coupled
the decomposition
kinetics
of these
species
oscilla(QET theory).
198
Ion signal Of rmduct ion
t
M: H+(NH&-NHq++NH3 ClD:H+(NH3)2+X--NHq++NH3+X
Collision induced dissociation
Unimoleculer decay ( M) 2.5 Gas
pressure
5 in field free region
FIG ,1
z5.10 (Tom)
-5
>
100
I,
I50 I
,
Stagnation
I,
,
gas
,
,
,
200 ,
,
,
,
,
temperature('K)
FIG,~
REFERENCES
1
A.J. State and A.K. Shukla, Int. J. Mass Spectrom. Ion Phys., 36 (1980) 119 - 122 A.J. State and A.K. Shukta, Chem. Phys. Lett., 85 (1982) 157 - 160 A-J. State and A.K. Shukla, J. Phys. Chem., 86 (1982) 865 - 867 J. Sunner and P. Kebarle, J. Phys. Chem., 85 (1981) 327 - 335 J-H.. Futrell, K. Stephan, A.W. Castleman, Jr., and J.D. Mark, Proc. 8th Int. Symp. Molecular Beams, Cannes (19811 262 - 265 K. Stephan and T.D. Mgrk, Chem. Phys. Lett., 87 (1982) 226 - 228 6 J.H. Futrell, K. Stephan, and T.D. M;irk, J. Chem. Phys., June, 1982 7 K. Stephan, T.D. MBrk, J.H. Futrell and A.W. Castleman, Jr., Vacuum 8 TAIP, in print K. Stephan, T.D. mrk, E. MZrk, A. Stamatovic, N. Djuric, and A.W. 9 in print Castleman, Jr., Beitr. Plasmaphysik, 20 K. Stephan and T.D. MSrk, Chem. Phys. Lett., in print Futrell, E. fit-k, K.I. Peterson, 11 T-D_ M;irk, K. Stephan, H. Helm, J-H. N. Djuric and A. Stamatovic, SASP, 3(1982) 7 - 18 A.W. Castleman, Jr., 12 H. Helm, K. Stephan and T.D. M;irk, Phys. Rev., A 19 (1979) 2154 - 2160 K. Stephan, H. Helm and T.D. &r-k, J. Chem. Phys., 73 (1980) 3763 - 3778 1: H. Helm, K. Stephan, T.D. M;irk and D.L. Huestis, J. Chem.Phys., 74 (1981) 3844 - 3851 R.G. Cooks, J.H. Beynon, R.M. Caprioli, and G.R. Lester, Metastable 15 Ions (Elsevier, Amsterdam, 1973) E. M;irk, T.D. l%rk, Y.B. Kim and K. Stephan, J. Chem. Phys., 75 (1983) 16 4446 - 4453 Work supported by Usterr. Forschungsfonds under Projekt S-18/05 and S-18/08.