1. FTIR Observation and DFT Study of CoC 3 Trapped in Solid Ar S.A. Bates, J.A. Rhodes, C.M.L. Rittby, and W.R.M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129 62 nd Meeting of the International Symposium on Molecular Spectroscopy The Ohio State University June 18-22, 2007

2. 2 Metallocarbohedrenes Small metal carbon clusters important in understanding their formation and bonding (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 clusters (Castleman, JPC 1992; Tono, JCP 2002) Co n C m species form from Co atoms attaching to carbon aggregates. (Tono, JCP 2002) Motivation

3. 3 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) (Li & Wang, JCP 1999; Wang & Li, JCP 2000) CoC 2 metal-carbon stretch measured at 540(60) cm -1. (Li & Wang, JCP 1999) No vibrational features were resolved for CoC 3 so excluded from DFT investigation – geometry undetermined. (Wang & Li, JCP 2000)

4. 4 Motivation DFT predicts cyclic (C 2v ) CoC 2 ground state (Arbuznikov & Hendrickx, CPL 2000; Yuan et al., Chin. PL 2006) DFT predicted Co 2 C 3 structure has C 2v symmetry with equivalent C atoms, supported by PE spectra (Tono, JCP 2002) Co

5. 5 Motivation Recent TCU Molecular Physics lab metal-carbon species identifications include Fan-shaped (C 2v ) TiC 3 (Kinzer, JCP 2006) and ScC 3 (Kinzer, JCP, to be submitted) Linear CrC 3 (Bates, JCP 2006), AlC 3, AlC 3 Al (Bates, JCP, to be submitted), and NiC 3 Ni (Kinzer, JCP, to be submitted) See following talk (RE04) on NiC 3 Ni (Kinzer, Matrix/Condensed Phase)

6. 6 Research Objectives To measure the vibrational fundamentals and 13 C isotopic shifts of metal carbon species (MC n ) 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. 13 C shifts are essential to species identification and structure determination.

7. 7 Experimental Apparatus Nd-YAG 1064 nm pulsed laser Quartz window Laser focusing lens Ar To pump 10 -7 Torr or better CsI window To pump 10 -3 Torr Carbon rod Cobalt rod Gold mirror ~10 K Bomem DA3.16 Fourier Transform Spectrometer KBr beam splitter liquid N 2 cooled MCT detector (550-3900 cm -1 )

8. 1800 1850 1900 1950 2000 2050 2100 2150 C 12 C7C7 C 11 C 10 C 11 C6C6 C9C9 C3C3 C8C8 C 10 C9C9 C7C7 C5C5 Frequency (cm -1 ) Absorbance (a) Co rod + 12 C rod (b) 12 C rod ν3ν3 2164.1 ν4ν4 2127.8 ν5ν5 2078.1 ν6ν6 2074.9 ν5ν5 2071.7 2038.9 ν3ν3 1998.0 ν6ν6 1952.5 ν5ν5 1946.1 ν7ν7 1915.8 ν7ν7 1894.3 ν5ν5 1856.7 ν8ν8 ν9ν9 1818.0 C6ˉC6ˉ 1936.7 1918.2

9. 1840 1850 1860 1870 1880 1890 1900 1910 1920 Frequency (cm -1 ) Absorbance Co rod + 20% 13 C rod 1906.4 1918.2 1905.2 1870.8 1914.5 1922.5 1894.3 1886.4 1880.2 ν5(u)C7ν5(u)C7 Kranze, JCP 1996 C7C7 C7C7 C 7 1870.4 C6ˉC6ˉ Bates, unpublished work C4OC4O Maier, Angew. Chem. 1988

10. 1840 1850 1860 1870 1880 1890 1900 1910 1920 Frequency (cm -1 ) Absorbance Co rod + 20% 13 C rod 1906.4 1918.2 1905.2 1870.8 Three remaining features Nominal enrichment: 20% 13 C Observed effective enrichment: 9% (based on other C n species) Three features are consistent with a molecule containing three inequivalent C atoms. Linear CoC 3 ?

11. 1840 1850 1860 1870 1880 1890 1900 1910 1920 Frequency (cm -1 ) Absorbance Co rod + 30% 13 C rod Co rod + 20% 13 C rod 1918.2 1844.2 1857.8 1858.8 1892.9 1906.4 1905.2 1870.8 CHO Milligan & Jacox, JCP 1969 1906.4 1905.2 1870.8 Single 13 C shifts? Double 13 C shifts? Full 13 C shift (i.e. Co 13 C 3 )?

12. 12 More Evidence – Intensity Ratios Ratios of the intensities of 13 C isotopomers to the full 12 C isotopomer IsotopomerC3C3 CoC 3 ? Single 13 C~10%~9% Double 13 C~4% Full 13 C~10%~9% Spectra exhibit non-randomization. Compare isotopomer intensities to ν 3 (  u ) =2038.9 cm -1 mode of C 3 because 1918.2 cm -1 is a candidate for CoC 3.

13. 13 Calculations: Linear and C 2v Isomers of CoC 3 DFT B3LYP/6-311+G(3df) predicted vibrational frequencies and intensities CoC 3 Isomer Vibrational Mode Frequency (cm -1 ) Infrared intensity (km/mol) 2Δ2Δ ν1(σ)ν1(σ)2014586 linearν2(σ)ν2(σ)13583 ν3(σ)ν3(σ)49718 ν4(π)ν4(π)38529 ν5(π)ν5(π)142~0 2B12B1 ν1(a1)ν1(a1)12409 fanlike (C 2v )ν2(a1)ν2(a1)67115 ν3(a1)ν3(a1)45815 ν4(b1)ν4(b1)3718 ν5(b2)ν5(b2)156379 ν6(b2)ν6(b2)37322 Co (1918.2) Co 0.0 kcal/mol +3.7 kcal/mol

14. 14 Theoretical Calculations Used DFT with B3LYP functional and 6-311+G(3df) basis set in Gaussian 03 program suite Calculations performed for linear and C 2v (fan) structures of CoC 3 Also investigated various Co 2 C 3 geometries that were consistent with our FTIR isotopic spectra, but no stable minimum structures with a vibrational fundamental in the right frequency region obtained See talk WH09 (Garcia, Theoretical/Computational Spectroscopy)

15. Co rod + 30% 13 C rod 30% 13 C B3LYP simulation 1840 1850 1860 1870 1880 1890 1900 1910 1920 Absorbance Frequency (cm -1 ) 1906.4 1918.2 1905.2 1870.8 Single 13 C shifts 1857.8 1858.8 1892.9 Double 13 C shifts 1844.2 Full 13 C shift (i.e. Co 13 C 3 )

16. 16 Calculations: Isotopic Shift Frequencies for the ν 1 ( σ ) Mode of Linear CoC 3 IsotopomerObserved B3LYP/ 6-311+G(3df) ScaledDifference Co-C-C-C ν obs ν DFT ν sc Δν=ν obs -ν sc 59-12-12-12(A)1918.22013.6…a…a … 59-13-12-12(B)1905.22000.51905.7-0.5 59-12-13-12(C)1870.81962.11869.11.7 59-12-12-13(D)1906.42000.71905.90.5 59-13-13-13(A')1844.21934.4…b…b … 59-12-13-13(B')1858.81949.01858.10.7 59-13-12-13(C')1892.91986.71894.1-1.2 59-13-13-12(D')1857.81948.51857.60.2 a DFT calculations scaled by a factor of 1918.2/2013.6=0.95262. b DFT calculations scaled by a factor of 1844.2/1934.4=0.95337.

17. Co rod + 30% 13 C rod 30% 13 C B3LYP simulation 1840 1850 1860 1870 1880 1890 1900 1910 1920 Absorbance Frequency (cm -1 ) 1918.2 (A) 59-12-12-12 1905.2 (B) 59-13-12-12 1892.9 (C') 59-13-12-13 1906.4 (D) 59-12-12-13 1857.8 (D') 59-13-13-12 1858.8 (B') 59-12-13-13 1844.2 (A') 59-13-13-13 1870.8 (C) 59-12-13-12

18. 18 Conclusions DFT calculations with B3LYP and BPW91 functionals predict the fan and linear isomers are within a few kcal/mol. Lowest energy isomer: BPW91 – 2 B 1 fan B3LYP – 2 Δ linear Calculations do not provide a clear answer for the ground state of CoC 3. Linear CoC 3 was observed in its 2 Δ ground state. The ν 1 ( σ ) C–C stretch has been identified at 1918.2 cm -1. Co

19. 19 Conclusions No evidence of fan-shaped isomer despite a careful search of the FTIR spectra. TiC 3 : Fan-shaped TiC 3 predicted as lowest energy isomer, well-separated energetically from competing linear and kite structures. (Kinzer, JCP 2006) AlC 3 and CrC 3 : AlC 3 predicted to have close-lying linear, kite, and fan-shaped isomers (Barrientos, CPL 2000; Bates, JCP, to be submitted). CrC 3 predicted to have close-lying fan and linear isomers (Zhai, JCP 2004; Bates, JCP 2006). For both AlC 3 and CrC 3, linear isomers observed. Careful searching revealed no evidence of non-linear isomers. This work has been accepted for publication in the Journal of Chemical Physics.

20. 20 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)

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