1 / 20

FTIR Isotopic and DFT Studies of Transition Metal-Carbon Clusters Condensed in Solid Argon: CrC 3

FTIR Isotopic and DFT Studies of Transition Metal-Carbon Clusters Condensed in Solid Argon: CrC 3. S.A. Bates, C.M.L. Rittby, and W.R.M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129

mortimer-coulon
Télécharger la présentation

FTIR Isotopic and DFT Studies of Transition Metal-Carbon Clusters Condensed in Solid Argon: CrC 3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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 IRC+10216 (Cernicharo, A&A, 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 IRC+10216 include SiCN and SiC3(Apponi, ApJ, 1999; Guélin, A&A, 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 (M=Sc, V, Cr, Mn, Fe, Co, and Ni) (Wang & Li, JCP, 1999; Wang & Li, JCP, 2000)

  4. Motivation nearly isoenergetic Uncertain ground state for CrC3(Zhai, JCP, 2004) DFT predictions for the lowest energy isomers of CrC3ˉand 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 Nd:YAG 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 (n>6). • But for small clusters (n<5), using ~50% 13C enrichment produces all of the 13C isotopomers.

  7. Experimental Procedures Nd:YAG 1064 nm pulsed laser laser focusing lens CsI window quartz window gold mirror ~10 K Bomem DA3.16 Fourier Transform Spectrometer • KBr beam splitter • liquid N2 cooled MCT detector (550-3900 cm-1) to pump 10-7Torr or better to pump 10-3Torr carbon rod transition metal rod Ar See previous talk, WG04 (Gonzalez, Matrix/Condensed Phase)

  8. 1700 1750 1800 1850 1900 1950 2000 2050 2100 2150 ν5 ν7 ν6 ν4 ν6 C7 ν3 C11 C7 C10 ν3 C9 C5 C3 1894.3 ν9 2074.9 1946.1 2127.8 1998.0 ν5 C12 ν5 ν7 2164.1 2038.9 C6 C10 C8 ν8 ν5 C11 1818.0 C9 1952.5 12C rod + Cr rod 1915.8 2071.7 ν9 1856.7 2078.1 C8 1789.5 1710.5 Absorption 12C rod Frequency (cm-1)

  9. Unidentified feature in pure 12C spectrum C3¯ (Szczepanski, JPCA, 1997) CrOCO (Souter, JACS, 1997) 1720 1730 1740 1750 1760 1770 1780 1790 Cr rod + 15% 13C rod 1789.5 Absorption 1721.8 1735.1 1777.8 1746.1 1779.7 1743.4 Frequency (cm-1)

  10. 1720 1730 1740 1750 1760 1770 1780 1790 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. Cr rod + 30% 13C rod Single 13C isotopic substitutions 1720.6 Double 13C isotopic substitutions Full 13C substitution, i.e. Cr13C3 1731.4 1733.5 1777.8 1767.1 1779.7 1743.4 1720 1730 1740 1750 1760 1770 1780 1790 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 6-311+G(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. Single 13C isotopic substitutions Double 13C isotopic substitutions 1720 1730 1740 1750 1760 1770 1780 1790 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 ν1(σ) Mode of Linear CrC3 Comparison of observed vibrational frequencies (cm-1) of the ν1(σ) mode for 13C-substituted isotopomers of linear CrC3 with the predictions of B3LYP/6-311G + (3df) calculations aDFT calculations scaled by a factor of 1789.5/1947.4=0.91892.

  16. 52-12-12-12 52-13-13-13 (A) (A') 52-13-13-12 (D') 52-12-12-13 (D) 52-12-13-13 52-13-12-12 (B') (B) 52-13-12-13 52-12-13-12 (C') (C) 1720 1730 1740 1750 1760 1770 1780 1790 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 ν1(σ) 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 ν1(σ) 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 • D.N. Davis, Astrophys. J. 106, 28 (1947). • J. Cernicharo and M. Guélin, Astron. and Astrophys. 183, L10 (1987). • L.M. Ziurys, C. Savage, J.L. Highberger, A.J. Apponi, M. Guélin, and J. Cernicharo, Astrophys. J. 564, L45 (2002). • J.L. Highberger, C.S. Savage, J.H. Bieging, and L.M. Ziurys, Astrophys. J. 562, 790 (2001). • A.J. Apponi, M.C. McCarthy, C.A. Gottlieb, and P. Thaddeus, Astrophys. J. 516, L103 (1999). • M. Guélin, S. Muller, J. Cernicharo, A.J. Apponi, M.C. McCarthy, C.A. Gottlieb, and P. Thaddeus, Astron. and Astrophys. 363, L9 (2000). • K.H. Hinkle, J.J. Keady, and P.F. Bernath, Science 241, 1319 (1988). • J. Cernicharo, J.R. Goicoechea, and E. Caux, Astrophys. J. 534, L199 (2000). • P.F. Bernath, K.H. Hinkle, and J.J. Keady, Science 244, 562 (1989). • B.C. Guo, K.P. Kerns, and A.W. Castleman, Jr., Science 255, 1411 (1992).

  20. References • B.C. Guo and A.W. Castleman, Jr., in Advances in Metal and Semiconductor Clusters, ed. M.A. Duncan (Jai Press, London, 1994), Vol. 2, 137. • S.E. Kooi, B.D. Leskiw, and A.W. Castleman, Jr., Nano Letters 1, 113 (2001). • S. Wei, B.C. Guo, J. Purnell, S. Buzza, and A.W. Castleman, Jr., J. Phys. Chem. 96, 4166 (1992). • K. Tono, A. Terasaki, T. Ohta, and T. Kondow, J. Chem. Phys. 117, 7010 (2002). • S.-L. Wang and X. Li, J. Chem. Phys. 112, 3602 (2000). • H.-J. Zhai, L.-S. Wang, P. Jena, G. L. Gustev, and C.W. Bauschlicher, Jr., J. Chem. Phys. 120, 8996 (2004). • M.E. Jacox, NIST Vibrational and Electronic Energy Levels Database (http://webbook.nist.gov/chemistry) • J. Szczepanski, S. Eckern, C. Chapo, and M. Vala, Chem. Phys. 211, 359 (1996). • P.F. Souter and L. Andrews, J. Am. Chem. Soc. 119, 7350 (1997). • J. Szczepanski, C. Wehlburg, M. Vala, J. Phys. Chem. A 101, 7039 (1997).

More Related