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VIBRATIONAL SPECTROSCOPY OF GERMANIUM-CARBON CLUSTERS: ν 4 ( σ u ) MODE OF GeC 5 Ge

VIBRATIONAL SPECTROSCOPY OF GERMANIUM-CARBON CLUSTERS: ν 4 ( σ u ) MODE OF GeC 5 Ge. E. Gonzalez, C.M.L. Rittby, and W.R.M. Graham Texas Christian University Molecular Physics Laboratory. Motivation. The Group IVB molecular clusters, Si n C m , Ge n C m , and

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VIBRATIONAL SPECTROSCOPY OF GERMANIUM-CARBON CLUSTERS: ν 4 ( σ u ) MODE OF GeC 5 Ge

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  1. VIBRATIONAL SPECTROSCOPY OF GERMANIUM-CARBON CLUSTERS: ν4(σu) MODE OF GeC5Ge E. Gonzalez, C.M.L. Rittby, and W.R.M. Graham Texas Christian University Molecular Physics Laboratory

  2. 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?

  3. 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

  4. 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 Germanium Carbon Ar flow

  5. 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.

  6. 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.

  7. Isotopomers probability of Cn bearing species: 13 13 13 12 12 12 12 12 12 12 : Number of carbon atoms : Number of 13C isotopic substitutions : 13C concentration Carbon Rods Homemade carbon rods with the desired ratio of 13C:12C by mass weight.

  8. Single substitutions Example: C5 bearing species Double substitutions Triple substitutions Quadruple substitutions Probability 0.1 Low 13C High 13C 0.08 0.06 0.04 0.02 20 40 60 80 100 13C Concentration

  9. 13-13-13-13-13 2080 2090 2100 2110 2120 2130 2140 2150 2160 C5 90% 12C/10% 13C 10% 12C/90% 13C 12-12-12-12-12 12-13-13-13-13 13-12-12-12-12 Absorbance 12-13-12-12-12 13-12-13-13-13 13-13-12-13-13 12-12-13-12-12 12C12,v7 Frequency (cm-1)

  10. n6 C9 Cn n3 1936.7 1998.0 GeC3Ge n5 GenCm n1 C6 GeC7 n4 2093.2 1952.5 GeC9 2063.8 n4 n3 1928.3 C7 C5 C7 2127.8 2164.1 1894.3 2150 1750 1800 1850 1900 1950 2000 2050 2100 (a) 12C rod + Ge rod GenCm 1920.3 2158.0 n9 n3 n7 C3 C12 n5 C11 n7 n8 1818.0 C10 1946.1 2038.9 C11 Absorbance 1915.8 1856.7 (b) 12C rod

  11. (I) (D),(H) (G) (C),(F) 2170 2100 2110 2120 2130 2140 2150 2160 Frequency (cm-1) (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) 2138.2 2142.3 2116.8 2116.3 2123.4 2105.2 2154.2

  12. (D') (B' ) (H' ) (I' ) 2077.8 2070 2080 2090 2100 2110 2120 2130 2140 2150 Frequency (cm-1) (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 2116.6 2120.2 Absorbance

  13. 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.

  14. 1.2918 1.2897 1.7897 DFT predicted (B3LYP/cc-pVDZ) ground state geometry for GeC5Ge cluster Ge 1.2897 1.2918 1.7897 Å Ge

  15. C5 GeC5Ge 2163.9 2158.0 calculated 4592 km/mol calculated 2539 km/mol 2140 2160 2180 DFT B3LYP/cc-pVDZ predicted vibrational frequencies (cm-1) and band intensities for the linear GeC5Ge

  16. Statistical Analysis Molecule Exp. Frq. Theo. Frq Ratio Molecule Exp. Frq. Theo. Frq Ratio 2400.0 y = 0.9557x + 13.661 2 R = 0.969 2200.0 2000.0 1800.0 Experimetal Frequencies (cm-1) 1600.0 1400.0 1200.0 1000.0 1000.0 1500.0 2000.0 2500.0 Theoretical Frequencies (cm-1)

  17. Statistical Analysis Molecule Exp. Frq. Theo. Frq Ratio Theoretical Frequency: 2135.0 cm-1 Expected Experimental Frequency: (2054 ± 133) cm-1 (using linear regression) 1921 cm-1 2187 cm-1 ] [ 2158 cm-1!

  18. Comparison of observed vibrational frequencies (cm-1) of the 4(σu) mode for 13C- substituted isotopomers of linear GeC5Gewith the predictions of B3LYP/cc-pVDZ level calculations. aResults of the DFT-B3LYP/cc-pVDZ calculation scaled by a factor of 2158.0/2135.0=1.01076. bOverlapped by band C.  cOverlapped by band D.

  19. (a) Ge rod and 15% 13C rod (A) C5 C5 single substitutions C5 double substitutions C7 2158.0 2164.1 2127.9 C12 (B) 2140.0 Cn 2155.1 (I) (D),(H) (G) (C),(F) (J) Absorbance (E) 2123.4 2138.2 2142.3 2116.8 2116.3 2105.2 2154.2 (B) (C),(F) (b) DFT simulation 15% 13C (D) (H) (J) (I) (G) (E) 2170 2110 2120 2130 2140 2150 2160 2100 Frequency (cm-1)

  20. Comparison of observed vibrational frequencies (cm-1) of the 4(σu) mode for 12C- substitutedisotopomers of linear GeC5Gewith the predictions of B3LYP/cc-pVDZ level calculations. aResults of the DFT-B3LYP/cc-pVDZ calculation scaled by a factor of 2074.7/2051.0=1.0116. bOverlapped by 3(σu) mode of 13C5. cOverlapped by C5 double-12C isotopomer shift.

  21. C5 (a) Ge rod and 85% 13C rod (A´) C5 single substitutions C5 double substitutions 2080.4 2074.7 (B´) (H´) (D´) (I´) (C´),(F´) 2114.4 2116.6 2120.2 2077.8 2098.8 Absorbance (B´) (C´),(F´) (b) DFT simulation 85% 13C (D´) (E´) (G´) (H´) (I´) (J´) 2070 2080 2090 2100 2110 2120 2130 2140 2150 Frequency (cm-1)

  22. 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 ν4(σu) vibrational fundamental at 2158.0 cm-1 .

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

  24. References(1)

  25. References(2)

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