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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
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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
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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
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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 More specific than “near” or “surrounding”?
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Astrophysical Motivation
H2S NaCN SiH4 PN C5 C2 NH3 KCN SiC4 CP C3 C8H CH4 AlNC SiCN CH3CN HC2N C7H H2CCH2 MgCN SiC3 c-C3H2 H2C6 C6H HNC MgNC SiC2 HC4N H2C4 C5H HCCH AlF SiN C5N HC9N C4H HCN KCl SiC C3N HC7N C3O CN AlCl SiS C3S HC5N C3H CS NaCL SiO CCS HC3N CCH CO Confirmed Molecules in IRC+10216 Source: L.M. Ziurys, Proc. Nat. Acad. Sci., 2006.
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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.
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Previous Experimental Research
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) NiC3 Ni Ni2 Ni2C3 NiC10 Ni2C6 Ni2C11 NiC16 J.E. Reddic and M.A. Duncan, Chem. Phys. Lett. 264, 157 (1997).
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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 NiC2 Ni2C4 NiC3 Ni2C5 NiC4 Ni2C6 NiC5 Ni2C7 NiC6 Ni2C8 Ni2C9 Ni2C10 Ni2C11 Gold text denotes clusters studied by Andriotis et al. All were studied by Gallego et al. Andriotis (CPL 1999); Gallego (PR B 2000)
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Previous Theoretical Research - NiC3
1.626 Å 1.299 1.280 Ni C 1.832 1.330 1.887 Ni C linear ~4 - 8 kcal/mol Ni C fan-like 0 kcal/mol predicted ground state kite ~17 kcal/mol Andriotis (PR B 2001); Gallego (PR B 2003)
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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 ( cm-1) 0.2 cm-1 resolution To pump 10-7 Torr or better To pump 10-3 Torr Nickel rod Carbon rod Ar
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1950.8 12C + Ni spectrum, after annealing at 24 K C3 ν3 2038.9 C6 C6¯
Absorbance C6¯ C7 ν5 1894.3 C6 ν4 1952.5 C9 ν6 1998.0 (b) Pure 12C spectrum C12 ν9 1818.0 1800 1850 1900 1950 2000 2050 2100 Frequency (cm-1)
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Symmetry: two equivalent C atoms, one unique
1950.8 (a) 88 % 12C / 12% 13C + Ni, after annealing at 25 K ~ C7 isotopic shifts ■ ~ C6 isotopic shifts C6 1875.5 1889.7 1903.2 1924.5 1938.1 C7 ■ C6¯ 1898.2 Absorbance (b) 50 % 12C / 50% 13C + Ni, after annealing at 24 K Note: isotopic shift pattern resembles the C3 ( cm-1) shift pattern. Symmetry: two equivalent C atoms, one unique Frequency observed at cm-1 → likely a linear molecule Contains linear C3 → linear NiC3Ni is a likely candidate! 1860 1880 1900 1920 1940 1960 Frequency (cm-1)
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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
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Theoretical Modeling of NiC3Ni
Relative energy (kcal/mol) Imaginary Frequencies (cm-1) C-C-C angle Linear 1Σg ~5 x 10– 4 55i 180° 3? ~23 393i,160i,33i 5Σg ~56 1235i,593i Relaxed 1A1 none ~178° 3B1 ~22 ~173° 5A2 ~3.4 243i Singlet linear & relaxed 177.9° 179.2° 1.29 Å 1.64 Å Relaxing the molecule suggests NiC3Ni may be “floppy”. Singlet “linear” and “relaxed” bond lengths are equal. Both models produce similar vibrational fundamentals.
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DFT-B3LYP/6-311G* predicted vibrational fundamentals for NiC3Ni (1Σg)
Vibrational mode Frequency (cm-1) Infrared intensity (km/mol) ν1(σg) 1518 ν2(σg) 325 ν3(σu) 2076 2676 ν4(σu) 786 28 ν5(πg) 275 ν6(πu) 140 77 ν7(πu) 55i 1.6 1950.8? ν3(σu)
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(a) 88 % 12C / 12% 13C + Ni, after annealing at 25 K
1950.8 (a) 88 % 12C / 12% 13C + Ni, after annealing at 25 K ~ C7 isotopic shifts ■ ~ C6 isotopic shifts C6 1875.5 1889.7 1903.2 1924.5 1938.1 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)
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Comparison of Isotopic Shifts
Isotopomer Observed νobs (cm-1) B3LYP/6-311G* Calculated νDFT (cm-1) Scaled νSC Difference νobs –νSC Ni Ni 1950.8 2075.9 --- Ni Ni 1938.1 2061.3 1937.1a 1.0 Ni Ni 1903.2 2025.9 1903.8a -0.6 Ni Ni 1875.5 1994.3 Ni Ni 1889.7 2010.9 1891.1b -1.4 Ni Ni 1924.5 2045.5 1923.7b 0.8 THIS SHOULD BE THE CORRECT TABLE!!! a Scaled using scaling factor /2075.9= b Scaled using scaling factor /1994.3= Two scaling factors are used to account for anharmonic effects.
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Conclusions The ν3(σu) = 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. 1.64 Ǻ 1.29 Ǻ This work is being submitted to the Journal of Chemical Physics.
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Acknowledgements The Welch Foundation
TCU Research and Creative Activities Fund in support of this research W.M. Keck Foundation for the Bomem spectrometer
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References Cologne Database for Molecular Spectroscopy < L.M. Ziurys, Proc. Nat. Acad. Sci. 103, (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, (2000). G. E. Froudakis, M. Mühlhäuser, A. N. Andriotis, and M. Menon, Phys. Rev. B 64, (2001). R. C. Longo, M. M. G. Alemany, B. Fernández, and L. J. Gallego, Phys. Rev. B 68, (2003). R. C. Longo and L. J. Gallego, J. Chem. Phys. 118, (2003).
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