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FTIR Matrix and DFT Study of the Vibrational Spectrum of NiC 3 Ni

FTIR Matrix and DFT Study of the Vibrational Spectrum of NiC 3 Ni. R.E. Kinzer, Jr., C. M. L. Rittby, W. R. M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129. 62 nd International Symposium on Molecular Spectroscopy The Ohio State University

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FTIR Matrix and DFT Study of the Vibrational Spectrum of NiC 3 Ni

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  1. FTIR Matrix and DFT Study of the Vibrational Spectrum of NiC3Ni R.E. Kinzer, Jr., C. M. L. Rittby, W. R. M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129 62nd International Symposium on Molecular Spectroscopy The Ohio State University 18-22 June 2007

  2. Research Objectives • Synthesize small transition-metal carbide molecules • applications to metallocarbohedrenes (Bates, RE03) • potential astrophysical significance • Measure the infrared spectrum of the molecules • Fourier transform infrared (FTIR) spectroscopy • 13C isotopic substitution • Determine the vibrational fundamentals and molecular structure • Density functional theory (DFT) • 13C isotopic shift comparison

  3. Astrophysical Motivation • Transition-metal carbide clusters may potentially be observed in circumstellar shells. • Over 130 molecules have been observed in circumstellar shells or the interstellar medium (Cologne Database, May 2007). • Carbon clusters are observed in circumstellar shells. • e.g. C3, C4, C5 • Molecules bearing carbon chains are observed. • e.g. CCCN, HC4N, C5N, HC9N

  4. Astrophysical Motivation • Numerous metal-bearing molecules have been observed in circumstellar shells. • e.g. MgCN, AlNC, FeO • Transition-metals have been observed in F- to M-type circumstellar shells. • e.g. Mn, Fe, Cd • Molecules bearing transition-metals are observed in spectra of M-type stars. • e.g. TiO, VO, FeH, CrH

  5. Astrophysical Motivation Confirmed Molecules in IRC+10216 CO CCH HC3N CCS SiO NaCL CS C3H HC5N C3S SiS AlCl CN C3O HC7N C3N SiC KCl HCN C4H HC9N C5N SiN AlF HCCH C5H H2C4 HC4N SiC2 MgNC HNC C6H H2C6 c-C3H2 SiC3 MgCN H2CCH2 C7H HC2N CH3CN SiCN AlNC CH4 C8H C3 CP SiC4 KCN NH3 C2 C5 PN SiH4 NaCN H2S Source: L.M. Ziurys, Proc. Nat. Acad. Sci., 2006.

  6. Astrophysical Motivation • Before new molecules can be identified in astrophysical environments, their spectra must be found experimentally. • Few studies have measured transition-metal carbide spectra.

  7. Previous Experimental Research Ni NiC3 NiC10 Ni2C6 Ni2 Ni2C3 Ni2C11 NiC16 • Wang & Li (JCP 2000) photoelectron spectroscopy on MC3, M=Sc,V,Cr,Mn,Fe,Co,Ni • vibrational frequency of NiC3 at 480 ± 60 cm-1 • no DFT-B3LYP calculations for NiC3 • Mass spectroscopy (Reddic & Duncan, CPL 1997) • laser vaporization of graphite rod coated with Ni • distribution appears to fall off for higher masses (>250 amu) J.E. Reddic and M.A. Duncan, Chem. Phys. Lett. 264, 157 (1997).

  8. Previous Theoretical Research • Nickel carbides investigated by Andriotis et al. or Gallego et al. • There is disagreement on structures • Andriotis et al. calculated predominantly three-dimensional cage-like structures • Gallego et al. calculated linear or ring structures • both agree on fan-like NiC3 • Note: No previous theoretical results for Ni2C3 • Gold text denotes clusters studied by Andriotis et al. • All were studied by Gallego et al. Andriotis (CPL 1999); Gallego (PR B 2000)

  9. Previous Theoretical Research - NiC3 C 1.832 1.330 1.887 1.626 Å 1.299 1.280 C Ni Ni C C C C C Ni C C linear ~4 - 8 kcal/mol fan-like 0 kcal/mol predicted ground state kite ~17 kcal/mol Andriotis (PR B 2001); Gallego (PR B 2003)

  10. Experimental Apparatus Nd-YAG 1064 nm pulsed laser Laser focusing lens CsI window Quartz window Gold mirror ~ 10K • Bomem DA3.16 Fourier • Transform Spectrometer • • KBr beam splitter • • liquid N2 cooled MCT • detector (500 - 3500 cm-1) • 0.2 cm-1 resolution To pump 10-7Torr or better To pump 10-3Torr Carbon rod Nickel rod Ar

  11. C3ν3 2038.9 C7ν5 C6ν4 C9ν6 1894.3 1952.5 1998.0 C12ν9 1818.0 • 12C + Ni spectrum, • after annealing at 24 K 1950.8 C6 Absorbance C6¯ (b) Pure 12C spectrum 1800 1850 1900 1950 2000 2050 2100 Frequency (cm-1)

  12. ~ C7 isotopic shifts ■ ~ C6 isotopic shifts 1875.5 1889.7 1903.2 1924.5 1938.1 ■ ■ ■ ■ ■ ■ ■ 13-12-12 12-12-13 13-13-13 13-13-12 12-13-13 12-12-12 13-12-13 12-13-12 1950.8 (a) 88 % 12C / 12% 13C + Ni, after annealing at 25 K C6 C7 C6¯ 1898.2 Absorbance (b) 50 % 12C / 50% 13C + Ni, after annealing at 24 K • Symmetry: two equivalent C atoms, one unique • Frequency observed at 1950.8 cm-1 → likely a linear molecule • Contains linear C3 → linear NiC3Ni is a likely candidate! 1860 1880 1900 1920 1940 1960 Frequency (cm-1)

  13. Theoretical Modeling of NiC3Ni • Theoretical modeling of NiC3Ni • density functional theory (DFT) • Gaussian 03 program suite • B3LYP functional • 6-311G* basis set • 13C isotopic spectrum • simulated DFT spectrum is compared to experimental spectrum • allows for identification of molecular species and vibrational fundamentals

  14. Theoretical Modeling of NiC3Ni 1.29 Å 179.2° 177.9° 1.64 Å Singlet linear & relaxed • Relaxing the molecule • suggests NiC3Ni may be • “floppy”. • Singlet “linear” and • “relaxed” bond lengths • are equal. • Both models produce • similar vibrational • fundamentals.

  15. DFT-B3LYP/6-311G* predicted vibrational fundamentals for NiC3Ni (1Σg) ν3(σu) 1950.8?

  16. ~ C7 isotopic shifts ■ ~ C6 isotopic shifts 1875.5 1889.7 1903.2 1924.5 1938.1 ■ ■ ■ ■ ■ ■ ■ 13-12-12 12-12-13 13-13-13 13-13-12 12-13-13 12-12-12 13-12-13 12-13-12 1950.8 (a) 88 % 12C / 12% 13C + Ni, after annealing at 25 K C6 C7 C6¯ 1898.2 Absorbance (b) 50 % 12C / 50% 13C + Ni, after annealing at 24 K (c) DFT simulation 1860 1880 1900 1920 1940 1960 Frequency (cm-1)

  17. Comparison of Isotopic Shifts a Scaled using scaling factor 1950.8/2075.9=0.93974. b Scaled using scaling factor 1875.5/1994.3=0.94043. Two scaling factors are used to account for anharmonic effects.

  18. Conclusions 1.64 Ǻ 1.29 Ǻ • The ν3(σu) = 1950.8 cm-1 vibrational fundamental of NiC3Ni identified by comparison of 13C isotopic shifts measured by FTIR and calculated by DFT. • Theory at B3LYP/6-311G* level suggests the molecule may be “floppy”. • This is the first study to report on the structure and vibrational spectrum of NiC3Ni. This work is being submitted to the Journal of Chemical Physics.

  19. Acknowledgements • The Welch Foundation • TCU Research and Creative Activities Fund in support of this research • W.M. Keck Foundation for the Bomem spectrometer

  20. References • Cologne Database for Molecular Spectroscopy <http://www.ph1.uni-koeln.de/vorhersagen/>. • L.M. Ziurys, Proc. Nat. Acad. Sci. 103, 12274 (2006). • L. S. Wang and X. Li, J. Chem. Phys. 112, 3602 (2000). • J. E. Reddic and M. A. Duncan, Chem. Phys. Lett. 264, 157 (1996). • A. N. Andriotis, M. Menon, G. E. Froudakis, and J. E. Lowther, Chem. Phys. Lett. 301, 503 (1999). • C. Rey, M. M. G. Alemany, O. Diéguez, and L. J. Gallego, Phys. Rev. B 62, 12640 (2000). • G. E. Froudakis, M. Mühlhäuser, A. N. Andriotis, and M. Menon, Phys. Rev. B 64, 241401 (2001). • R. C. Longo, M. M. G. Alemany, B. Fernández, and L. J. Gallego, Phys. Rev. B 68, 167401 (2003). • R. C. Longo and L. J. Gallego, J. Chem. Phys. 118, 10349 (2003).

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