FTIR Isotopic and DFT Studies of Transition MetalCarbon Clusters Condensed in Solid Argon: CrC3

1
FTIR Isotopic and DFT Studies of Transition
Metal-Carbon Clusters Condensed in Solid Argon
CrC3
S.A. Bates, C.M.L. Rittby, and W.R.M. Graham
Department of Physics and Astronomy Texas
Christian University Fort Worth, TX 76129 61st
Meeting of the International Symposium on
Molecular Spectroscopy The Ohio State
University June 19-23, 2006
2
Motivation

• Astrophysical
• Metals observed in small molecules found in
  circumstellar shells and in the ISM
• CrO in M stars (Davis, ApJ, 1947)
• AlNC, NaCl in IRC10216
• (Cernicharo, AA, 1987 Ziurys, ApJ, 2002)
• NaCN, MgNC in CRL 2688 (Highberger, ApJ, 2001)
• Pure carbon chains observed in circumstellar
  shells (e.g. C3, C5)
• (Hinkle, Science, 1988 Cernicharo, ApJ, 2000
  Bernath, Science, 1989)
• Silicon-bearing species observed in IRC10216
  include SiCN and SiC3 (Apponi, ApJ, 1999
  Guélin, AA, 2000)
• See WH10 on TiC3 (Kinzer, Astronomical Species
  and Processes)

3
Motivation

• Metallocarbohedrenes
• Small metal carbon clusters important in
  understanding the formation of metcars
• (Guo, Science, 1992 Guo Castleman, Advances
  in Metal and Semiconductor Clusters, 1994
  Castleman, Nano Lett, 2001)
• TiC2, VC2 as building blocks for larger metcars
  
• (Castleman, JPC, 1992 Tono, JCP, 2002)
• Previous photoelectron spectroscopy (PES) and
  density functional theory (DFT) studies on MC2
  and MC3 clusters (MSc, V, Cr, Mn, Fe, Co, and
  Ni)
• (Wang Li, JCP, 1999 Wang Li, JCP, 2000)

4
Motivation

• Uncertain ground state for CrC3 (Zhai, JCP,
  2004)

DFT predictions for the lowest energy isomers of
CrC3 and CrC3
aDenotes ground state energy

• PES spectra
• Exhibit features consistent with both isomers.
• Abundance of C2v isomer increased with hotter
  source
• conditions indicating to the authors the linear
  isomer may be
• more stable.

5
Research Objectives

• To measure the vibrational fundamentals and
  isotopic shifts of metal carbon (MCn) species
  produced by NdYAG laser ablation and trapped in
  solid Ar at 10 K.
• To identify and determine the structures of the
  MCn species created by comparing Fourier
  transform Infrared (FTIR) measurements with DFT
  predictions.

6
Strategy

• 13C isotopic shifts necessary for species and
  structure determination.
• Low 13C enrichment (10) limits isotopic shifts
  to single 13C isotopomers, which is useful for
  large Cn clusters (ngt6).
• But for small clusters (nlt5), using 50 13C
  enrichment produces all of the 13C isotopomers.

7
Experimental Procedures
See previous talk, WG04 (Gonzalez,
Matrix/Condensed Phase)
8
?5
?7
?4
?6
?6
C7
?3
C11
C7
C10
?3
C9
C5
C3
1894.3
?9
2074.9
1946.1
2127.8
1998.0
?5
C12
?5
?7
2164.1
2038.9
C6
C10
C8
?8
?5
C11
1818.0
C9
1952.5
12C rod Cr rod
1915.8
2071.7
?9
1856.7
2078.1
C8
1789.5
1710.5
Absorption
12C rod
Frequency (cm-1)
9
Cr rod 15 13C rod
1789.5
Absorption
1721.8
1735.1
1777.8
1746.1
1779.7
1743.4
Frequency (cm-1)
10
Cr rod 15 13C rod
1789.5

• Three remaining features

• Nominal enrichment 15 13C
• Observed effective enrichment 7 (based on
• other Cn species)

Absorption

• Three features are consistent with a molecule
• containing three inequivalent C atoms.

Linear CrC3?
1777.8
1779.7
1743.4
Frequency (cm-1)
11
1789.5
Absorption
Cr rod 15 13C rod
1777.8
1779.7
1743.4
Frequency (cm-1)
12
Calculations Linear and C2v Isomers of CrC3
DFT (B3LYP/6-311G 3df) predicted vibrational
frequencies and intensities
(1789.5)
aFrequencies for fanlike structure initially
published by Wang and Li, 2000.
13
Theoretical Calculations

• Used Gaussian 03
• Used density functional theory (DFT) with B3LYP
  functional and 6-311G(3df) basis set
• Calculations performed for linear and C2v (fan)
  structures
• Calculations for C2v structure vibrational
  frequencies in good agreement with previous
  (Wang Li, JCP, 2000)
• 13C isotopic shift frequencies were also
  calculated for the linear isomer

14
Cr rod 30 13C rod
1789.5
1720.6
1731.4
1733.5
Absorption
1777.8
1767.1
1779.7
1743.4
Cr rod 15 13C rod
DFT simulation 10 13C
Frequency (cm-1)
15
Calculations Isotopic Shift Frequenciesfor the
?1(s) Mode of Linear CrC3
Comparison of observed vibrational frequencies
(cm-1) of the ?1(s) mode for 13C-substituted
isotopomers of linear CrC3 with the predictions
of B3LYP/6-311G (3df) calculations
aDFT calculations scaled by a factor of
1789.5/1947.40.91892.
16
Cr rod 30 13C rod
1789.5
1720.6
1731.4
Absorption
1779.5
1733.5
1777.8
1767.1
1743.3
DFT simulation 10 13C
Frequency (cm-1)
17
Conclusions

• The linear isomer of CrC3 has been observed.
• The ?1(s) mode is assigned to 1789.5 cm-1.
• No evidence of the C2v (fan) structure is
  observed.
• Four modes are predicted to lie within detector
  range.
• The strongest mode at 544 cm-1 is predicted to
  be 20 of the intensity of the ?1(s) mode of the
  linear structure and should be observable.
• Observation of the linear ground state structure
  is consistent with the thermal behavior in PES
  experiments.

18
Acknowledgments

• Our group would like to acknowledge funding from
• Welch Foundation
• TCU Research and Creative Activities Fund
  (TCURCAF)
• W.M. Keck Foundation
• Personal funding acknowledgments
• Barnett Scholarship
• Texas Space Grant Consortium Fellowship (TSGC)

19
References

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20
References

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