Transcript Jason_Dee_OSU_2009.ppt

Kinetic and Thermodynamic
Studies of Gaseous MetalloOrganic Complexes
Jason Dee, Darrin Bellert
Baylor University
June 25, 2009
Outline

What we do
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How we do it
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What we learn from it
What we do
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A major goal of our research is to obtain rate
constants of unimolecular decomposition of massselected metallo-organic ionic complexes via laserdriven photodissociation
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Investigate bond rupture dynamics and conditions
required to open various dissociative pathways in
metal catalyzed systems
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Custom built
molecular beam
apparatus
Orthogonal
Extraction
Hemispherical
energy analyzer
tuned to transmit
the full kinetic
energy of
molecular beam
Voltage tuned to
transmit solely
“daughter” ions
produced
following
photodissociation
S ig n a l ( a r b . u n its )
Mass Spectra of Ni+Acetaldehyde
Clusters Generated
5
Ni-Ald
4
3
2
Ni-Ald2
Ni
1
Ni-CO
Ni-Ald3
Ni-Ald4
0
50
150
mass (amu)
250
Ni-Ald5
Daughter fragments produced through
photodissociation of Ni+Acetaldehyde
S ig n a l
Ni
Ni-CO
300
350
400
450
500
550
600
Sector Voltage
Mass Daughter Ion
Mass Parent Complex

Sector Voltage for 
Parent Transmissi on
Sector Voltage for
DaughterTransmissi on
Possible mechanism for
decarbonylation of Ni+Acetaldehyde
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Left trace ~ Ni+
isertion into a C-H
bond followed by a
methide shift
Right trace ~ Ni+
insertion into a C-C
bond followed by a
hydride shift
How we measure rate constants
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Intersect molecular
beam with laser
before extraction
Sector to transmit
only ions with
appropriate
“daughter” kinetic
energy
Parent complex
must dissociate
after exiting the
acceleration grid
What we were anticipating…
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Laser must have
sufficient energy to
couple to dissociative
state
There is a time delay
after laser excitation
before dissociative
fragments are
detected
Plot ln [Int] vs time to
obtain rate constant
Don’t draw your line before
plotting your points…
What we are actually acquiring
At =A0e-kT
tf

y  A0 e  kt dt 
ti
A0   kti
A
 e  e  k   t  ti    0  e  kti  1  1 kt  


e 
k 
k 
 k' 
y   1.5k  A0e  k
e 
S ig n a l In te n s ity
Two representative
plots of
decarbonylation of
Ni+Acetaldehyde
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Top~18000 cm-1
Bottom~16,000 cm-1
Two Different
Pathways Observed
with different rate
constants
-10
+
Ni CO
Composite Simulation and
Observed Data
Individual Components (x10)
0
10
20
30
Time (microsec)
-10
40
50
60
Composite Simulation and
Observed Data
N i+ C O
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S i g n a l I n t e n s i t yN i + C O
+
Ni Ald→
Individual Components (x10)
0
10
20
30
Time (microsec)
40
50
Kinetic Scans of Ketones
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Rate constants
acquired after
deuterization of
Acetone were ~5x
greater than those
of normal acetone
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Vanessa
Castleberry’s talk on
Friday (FB05)
Comparing Ni+Ald to Ni+Ac
Ni+Ald→Ni+CO
C-C insertion
Internal energy
(cm-1)
k(E)
(µs-1)
C-H insertion
k(E)
(µs-1)
18,200
0.480 ± 0.002
0.100 ± 0.002
17,800
0.359 ± 0.002
0.095 ± 0.002
16,800
0.331 ± 0.002
0.085 ± 0.003
16,400
0.255 ± 0.003
0.076 ± 0.004
15,800
0.183 ± 0.005
0.052 ± 0.006
15,600
0.106 ± 0.008
0.050 ± 0.007
15,100
---------
---------
Internal energy
(cm-1)
k(E) (µs-1)
18800
0.113 ± 0.005
18000
0.087 ± 0.003
16400
0.059 ± 0.002
16100
0.058 ± 0.003
15600
0.055 ± 0.003
Ni+Ac→Ni+CO
What we learned from it
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Molecular Migration appears to be rate-limiting
step in simple ketones
From the Ni+Ald studies
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Ni+ insertion into either a C-H or C-C sigma bond is
possible
Isomerization Step appears to be rate limiting step
though further studies are needed
At lower energies, C-C insertion followed by a hydride
shift appears to predominate
Rate Constants dependent on energy of photon beam
Acknowldgements
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Baylor University
Petroleum Research Fund (PRF)
Dr. Darrin Bellert
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Bellert Research Group
Vanessa Castleberry
 Otsmar Villareal
 Ivanna Laboren
 Sarah Frey
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Any Questions?

Or post-doc positions…
N o r m a liz e d S ig n a l I n te n s ity
How cold is our molecular beam?
Fit experimental data
to Maxwell-Boltzmann
distribution of
velocities
 m(v( x)  u) 2 

P(v)  v exp 
2kT ( x) 

3
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Top~Pure He
expansion with Ni
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T = 12.2 K
M = 8.6
Bottom~Acetaldehyde
doped He expansion
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T = 0.32 K
M = 63
0.8
0.6
0.4
0.2
0
-0.2
N o r m a liz e d S ig n a l I n te n s ity
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1
1.4
1.6
1.8
2
2.2
2.4
Velocity (mm/microsec)
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
1.6
1.65
1.7
1.75
Velocity (mm/usec)
1.8
1.85