Presentation on theme: "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."— Presentation transcript:
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 st Meeting of the International Symposium on Molecular Spectroscopy The Ohio State University June 19-23, 2006
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 (Cernicharo, A&A, 1987; Ziurys, ApJ, 2002) NaCN, MgNC in CRL 2688 (Highberger, ApJ, 2001) –Pure carbon chains observed in circumstellar shells (e.g. C 3, C 5 ) (Hinkle, Science, 1988; Cernicharo, ApJ, 2000; Bernath, Science, 1989) –Silicon-bearing species observed in IRC include SiCN and SiC 3 (Apponi, ApJ, 1999; Guélin, A&A, 2000) –See WH10 on TiC 3 (Kinzer, Astronomical Species and Processes)
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) –TiC 2, VC 2 as “building blocks” for larger metcars (Castleman, JPC, 1992; Tono, JCP, 2002) Previous photoelectron spectroscopy (PES) and density functional theory (DFT) studies on MC 2 and MC 3 clusters (M=Sc, V, Cr, Mn, Fe, Co, and Ni) (Wang & Li, JCP, 1999; Wang & Li, JCP, 2000) Motivation
Uncertain ground state for CrC 3 (Zhai, JCP, 2004) Electronic configuration GeometryEnergy (eV) anion 4B14B1 fanlike (C 2v ) 0.0 a 4Σˉ4Σˉ linear+0.05 neutral 3B13B1 fanlike (C 2v ) 0.0 a 5Π5Π linear+0.30 DFT predictions for the lowest energy isomers of CrC 3 ˉ and CrC 3 a Denotes ground state energy nearly isoenergetic PES spectra Exhibit features consistent with both isomers. Abundance of C 2v isomer increased with hotter source conditions indicating to the authors the linear isomer may be more stable.
Research Objectives To measure the vibrational fundamentals and isotopic shifts of metal carbon (MC n ) species produced by Nd:YAG laser ablation and trapped in solid Ar at ~10 K. To identify and determine the structures of the MC n species created by comparing Fourier transform Infrared (FTIR) measurements with DFT predictions.
Strategy 13 C isotopic shifts necessary for species and structure determination. Low 13 C enrichment (~10%) limits isotopic shifts to single 13 C isotopomers, which is useful for large C n clusters (n>6). But for small clusters (n<5), using ~50% 13 C enrichment produces all of the 13 C isotopomers.
Experimental Procedures Ar Bomem DA3.16 Fourier Transform Spectrometer KBr beam splitter liquid N 2 cooled MCT detector ( cm -1 ) laser focusing lens Nd:YAG 1064 nm pulsed laser quartz window to pump Torr or better CsI window to pump Torr carbon rod transition metal rod gold mirror ~10 K See previous talk, WG04 (Gonzalez, Matrix/Condensed Phase)
C 12 C8C8 C7C7 C 11 C 10 C 11 C6C6 C9C9 C3C3 C8C8 C 10 C9C9 C7C7 C5C5 Frequency (cm -1 ) Absorption C rod + Cr rod 12 C rod ν3ν ν4ν ν5ν ν6ν ν5ν ν3ν ν6ν ν5ν ν7ν ν7ν ν5ν ν8ν8 ν9ν ν9ν
Absorption Frequency (cm -1 ) Cr rod + 15% 13 C rod C 3 ¯ (Szczepanski, JPCA, 1997) Unidentified feature in pure 12 C spectrum CrOCO (Souter, JACS, 1997)
Absorption Frequency (cm -1 ) Cr rod + 15% 13 C rod Three remaining features Linear CrC 3 ? Nominal enrichment: 15% 13 C Observed effective enrichment: 7% (based on other C n species) Three features are consistent with a molecule containing three inequivalent C atoms.
Absorption Frequency (cm -1 ) Cr rod + 30% 13 C rod Cr rod + 15% 13 C rod Single 13 C isotopic substitutions Double 13 C isotopic substitutions Full 13 C substitution, i.e. Cr 13 C 3
Calculations: Linear and C 2v Isomers of CrC 3 DFT (B3LYP/6-311G + 3df) predicted vibrational frequencies and intensities CrC 3 Isomer Vibrational Mode Frequency (cm -1 ) Infrared intensity (km/mol) 5Π5Πν1(σ)ν1(σ) linearν2(σ)ν2(σ)13472 ν3(σ)ν3(σ)50827 ν4(π)ν4(π)41724 ν5(π)ν5(π)1522 3B13B1 ν1(a1)ν1(a1)1306 a 8 fanlike (C 2v )ν2(a1)ν2(a1)8162 ν3(a1)ν3(a1)54463 ν4(b1)ν4(b1)51411 ν5(b2)ν5(b2)1473~0 ν6(b2)ν6(b2)38149 a Frequencies for fanlike structure initially published by Wang and Li, (1789.5)
Theoretical Calculations Used Gaussian 03 Used density functional theory (DFT) with B3LYP functional and G(3df) basis set Calculations performed for linear and C 2v (fan) structures Calculations for C 2v structure vibrational frequencies in good agreement with previous (Wang & Li, JCP, 2000) 13 C isotopic shift frequencies were also calculated for the linear isomer
Cr rod + 30% 13 C rod Cr rod + 15% 13 C rod Absorption Frequency (cm -1 ) Single 13 C isotopic substitutions DFT simulation 10% 13 C Double 13 C isotopic substitutions
Calculations: Isotopic Shift Frequencies for the ν 1 ( σ ) Mode of Linear CrC 3 Comparison of observed vibrational frequencies (cm -1 ) of the ν 1 ( σ ) mode for 13 C -substituted isotopomers of linear CrC 3 with the predictions of B3LYP/6-311G + (3df) calculations IsotopomerObserved B3LYP/ 6-311G+(3df) Scaled a Difference Cr-C-C-C ν obs ν DFT ν sc Δν=ν obs -ν sc (A) …… (B) (C) (D) (A') (B') (C') (D') a DFT calculations scaled by a factor of /1947.4=
Cr rod + 30% 13 C rod Absorption Frequency (cm -1 ) DFT simulation 10% 13 C (A') (C) (B') (D') (D) (B) (A) (C')
Conclusions The linear isomer of CrC 3 has been observed. The ν 1 ( σ ) mode is assigned to cm -1. No evidence of the C 2v (“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 ν 1 ( 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.
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)
References 1.D.N. Davis, Astrophys. J. 106, 28 (1947). 2.J. Cernicharo and M. Gu é lin, Astron. and Astrophys. 183, L10 (1987). 3.L.M. Ziurys, C. Savage, J.L. Highberger, A.J. Apponi, M. Gu é lin, and J. Cernicharo, Astrophys. J. 564, L45 (2002). 4.J.L. Highberger, C.S. Savage, J.H. Bieging, and L.M. Ziurys, Astrophys. J. 562, 790 (2001). 5.A.J. Apponi, M.C. McCarthy, C.A. Gottlieb, and P. Thaddeus, Astrophys. J. 516, L103 (1999). 6.M. Gu é lin, S. Muller, J. Cernicharo, A.J. Apponi, M.C. McCarthy, C.A. Gottlieb, and P. Thaddeus, Astron. and Astrophys. 363, L9 (2000). 7.K.H. Hinkle, J.J. Keady, and P.F. Bernath, Science 241, 1319 (1988). 8.J. Cernicharo, J.R. Goicoechea, and E. Caux, Astrophys. J. 534, L199 (2000). 9.P.F. Bernath, K.H. Hinkle, and J.J. Keady, Science 244, 562 (1989). 10.B.C. Guo, K.P. Kerns, and A.W. Castleman, Jr., Science 255, 1411 (1992).
References 11.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, S.E. Kooi, B.D. Leskiw, and A.W. Castleman, Jr., Nano Letters 1, 113 (2001). 13.S. Wei, B.C. Guo, J. Purnell, S. Buzza, and A.W. Castleman, Jr., J. Phys. Chem. 96, 4166 (1992). 14.K. Tono, A. Terasaki, T. Ohta, and T. Kondow, J. Chem. Phys. 117, 7010 (2002). 15.S.-L. Wang and X. Li, J. Chem. Phys. 112, 3602 (2000). 16.H.-J. Zhai, L.-S. Wang, P. Jena, G. L. Gustev, and C.W. Bauschlicher, Jr., J. Chem. Phys. 120, 8996 (2004). 17.M.E. Jacox, NIST Vibrational and Electronic Energy Levels Database (http://webbook.nist.gov/chemistry)http://webbook.nist.gov/chemistry 18.J. Szczepanski, S. Eckern, C. Chapo, and M. Vala, Chem. Phys. 211, 359 (1996). 19.P.F. Souter and L. Andrews, J. Am. Chem. Soc. 119, 7350 (1997). 20.J. Szczepanski, C. Wehlburg, M. Vala, J. Phys. Chem. A 101, 7039 (1997).