VIBRATIONAL SPECTROSCOPY OF GERMANIUM-CARBON CLUSTERS: ?4(su) MODE OF GeC5Ge

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VIBRATIONAL SPECTROSCOPY OF GERMANIUM-CARBON
CLUSTERS ?4(su) MODE OF GeC5Ge

• E. Gonzalez, C.M.L. Rittby, and W.R.M. Graham
• Texas Christian University
• Molecular Physics Laboratory

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Motivation

• The Group IVB molecular clusters, SinCm, GenCm,
  and
• SinCmGel, are of experimental and theoretical
  interest
• because of their novel structures and potential
  applications
• in semiconductor technology and microelectronics
• products (J. Karolczak,J. Chem. Phys. (1995), O.
  Leifeld, Nano. (1999).,
• O. Leifeld, Appl. Phys. Lett. (1999). ,R.
  Hartmann, Appl. Phys. Lett. (1998).)
• .

• Previously, we have reported vibrational spectra
  for
• SinCm (X.D. Ding, J. Chem, Phys. (1999) ) ,
  GenCm , and SinCmGel
• (D.L. Robbins, J. Chem. Phys. (2001,2002,2004).
  ) clusters. Could we
• form new species?

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Objectives

• To form novel germanium-carbon clusters by
  dual-laser
• ablation of germanium and carbon rods.

• Identify structure via isotopic shift
  measurements and
• assign the vibrational fundamentals

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Dual Laser Ablation Setup
laser focusing lenses
Nd-YAG 1064 nm pulsed lasers, 1.0 to 3.0 Watts
Gold mirror held held at 10 K
Quartz window
FTIR (MCT detector)
10-8Torr

CsI window
Carbon
Germanium
Ar flow
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Strategy

• To identify structure
• To measure frequencies and intensities of
  isotopomers
• formed by evaporating carbon rods with a 13C
  enrichment.

In order to limit the complexity of the isotopic
spectrum two experiments are carried out with
different carbon rods having low (5-30) and
high (70-95) 13C enrichment respectively. The
first one to obtain single and double 13C
substitutions, the second to obtain 12C
substitutions.
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Strategy (cont.)

• DFT Calculations
• To perform DFT calculations of geometries
  linked with the
• obtained spectra.

Isotopic shift calculation and simulated spectra
with the experimental 13C enrichment are
generated to sustain the identified structure and
vibrational assignment.
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Carbon Rods
Homemade carbon rods with the desired ratio of
13C12C by mass weight.
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Single substitutions
Example C5 bearing species
Double substitutions
Triple substitutions
Quadruple substitutions
Probability
0.1
High 13C
Low 13C
0.08
0.06
0.04
0.02
20
40
60
80
100
13C Concentration
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C5
90 12C / 10 13C
10 12C / 90 13C
12-12-12-12-12
13-12-12-12-12
12-13-13-13-13
Absorbance
12-13-12-12-12
13-12-13-13-13
12-12-13-12-12
13-13-12-13-13
12C12,v7
Frequency (cm-1)
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(a) 12C rod Ge rod
GenCm
1920.3
2158.0
n9
n3
n7
C3
C12
n5
C11
n7
n8
1818.0
C10
2038.9
1946.1
C11
Absorbance
1915.8
1856.7
(b) 12C rod
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(a) Ge rod and 15 13C rod
C5 single substitutions C5 double substitutions
C7
(A)
C5
2127.9
2158.0
2164.1
C12
2140.0
(B)
Cn
2155.1
(J)
Absorbance
(E)
2142.3
2138.2
2116.8
2116.3
2123.4
2105.2
2154.2
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(a) Ge rod and 85 13C rod
C5
2080.4
(A')
C5 single substitutions C5 double substitutions
2074.7
(C' ),(F' )
2098.8
2114.4
2120.2
2116.6
Absorbance
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DFT Calculations

• We did DFT calculations for GeC5Ge because
• It is consistent with the shown isotopic spectra.
  
• Previous experimental measurements and DFT
  calculations have shown that the original linear
  carbon chain structure is retained on the
  addition of a Si and Ge atom to one or both end.
  For example, SiC3Si, SiC4, SiC4Si, GeC3Ge, GeC7,
  GeC9, GeC3Si.

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DFT predicted (B3LYP/cc-pVDZ) ground state
geometry for GeC5Ge cluster
Ge
1.2897
1.2918
1.7897 Å
Ge
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DFT B3LYP/cc-pVDZ predicted vibrational
frequencies (cm-1) and band intensities for the
linear GeC5Ge
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Statistical Analysis
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Statistical Analysis
2158 cm-1!
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Comparison of observed vibrational frequencies
(cm-1) of the ?4(su) mode for 13C- substituted
isotopomers of linear GeC5Ge with the predictions
of B3LYP/cc-pVDZ level calculations.
aResults of the DFT-B3LYP/cc-pVDZ calculation
scaled by a factor of 2158.0/2135.01.01076.  bOve
rlapped by band C.  cOverlapped by band D.
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Comparison of observed vibrational frequencies
(cm-1) of the ?4(su) mode for 12C- substituted
isotopomers of linear GeC5Ge with the predictions
of B3LYP/cc-pVDZ level calculations.
aResults of the DFT-B3LYP/ cc-pVDZ calculation
scaled by a factor of 2074.7/2051.01.0116. bOverl
apped by ?3(su) mode of 13C5. cOverlapped
by C5 double-12C isotopomer shift.
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Conclusion

• The linear GeC5Ge germanium-carbon chain has been
  detected for the first time through the dual
  laser evaporation of graphite and germanium.

• FTIR isotopic shift measurements and DFT
  calculations at the B3LYP/cc-pVDZ level confirm
  the identification of the ?4(su) vibrational
  fundamental at 2158.0 cm-1 .

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• ACKNOWLEDGMENTS
•  
• The Welch Foundation
• TCU Research and Creative Activities Fund
• The W.M. Keck Foundation

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References(1)
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References(2)