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FTIR Matrix Study of Potential Circumstellar Molecules: TiC 3

FTIR Matrix Study of Potential Circumstellar Molecules: TiC 3. R.E. Kinzer, Jr., C. M. L. Rittby, W. R. M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129. 61 st International Symposium on Molecular Spectroscopy The Ohio State University

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FTIR Matrix Study of Potential Circumstellar Molecules: TiC 3

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  1. FTIR Matrix Study of Potential Circumstellar Molecules: TiC3 R.E. Kinzer, Jr., C. M. L. Rittby, W. R. M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129 61st International Symposium on Molecular Spectroscopy The Ohio State University 19-23 June 2006

  2. Astrophysical Potential • Carbon chains (e.g. C3, C5) and molecules containing carbon chains have been detected in interstellar space and circumstellar shells. (Hinkle, Science 1988; Bernath, Science 1989) • Molecules containing transition-metals have been detected in stars. • TiO is a signature of M-type stars. • The presence of TiC crystals and Ti bonded to fullerenes in post-AGB stars has been considered.(Duncan, Science 2000; Kimura, ApJ 2005) • See also WG05 on CrC3 (Bates, previous Matrix/Condensed phase session)

  3. Metallocarbohedrenes • Castleman et al. reported the Ti8C12+ metallocarbohedrene (“metcar”).(Science 1992) • Other large metal-carbide molecules have also been observed; TiC2 seems to serve as a building block.(Castleman, JPC 1992) • How do smaller transition-metal carbides (TiC2, TiC3, etc.) combine to form larger metcars, and what are their structures? • Photoelectron spectroscopy and theoretical studies of smaller transition-metal carbides have attempted to address this question.

  4. Photoelectron Spectroscopy (PES) Study • Wang et al. observed vibrationally resolved spectra of TiCnˉ, n=2-5. (JPCA 1997) • Only TiC2 had any previous theoretical study; it was predicted to have cyclic C2v structure. (Rheddy & Khanna, JPC 1994) • Structures proposed based on comparisons to theoretical studies of LaCn and YCn. • Cyclic structures were predicted for all molecules considered.

  5. Photoelectron Spectroscopy (PES) Study Wang et al., JPCA 1997.

  6. Theoretical DFT Study • Sumathi & Hendrickx Density Functional Theory (DFT) study using B3LYP functional for TiC2, TiC3, TiC4, Ti2C2, Ti2C3. (CPL 1998; JPCA 1998, JPCA 1999) • Vibrational frequencies calculated for singlet, triplet, and quintet states of several isomers. • Intensities of the modes not reported. Isomers of TiC3 considered

  7. Theoretical DFT Studies 97.2 s 100.0 86.8 s s 80.0 ~76 q Relative energy in kcal/mol q 67.9 60.0 t 59.8 t s q 55.1 50.6 40.0 s 54.5 q 41.2 t q 38.2 s t 20.0 38.9 36.0 q 27.4 t 28.9 21.5 0.0 s fan kite linear linear Non- planar Exo-Ti Exo-C VI VII I II VIII IV III 7.1 0.0 Relative energies for various isomers and electronic states of TiC3 Bond lengths (Å) for singlet, triplet (), and quintet isomers [ ].

  8. Theoretical DFT Study Vibrational mode DFT Calculated (cm-1) PES Observeda (cm-1) 1(a1) 1281.3 2(a1) 833.6 C C C 3(a1) 686.5 650 ± 30 4(b1) 591.2 5(b2) 1531.4 Ti 6(b2) 465.3 • The 1A1 state, C2v fan-like isomer is the ground state structure. a Observation by Wang et al., JPCA 1997.

  9. Strategy • Fourier Transform Infrared (FTIR) • measurements of vibrational frequencies • 13C isotopic shifts for clusters trapped in Ar at ~10 K. • Density Functional Theory (DFT) simulations • vibrational frequencies and intensities calculated for main 12C frequencies and 13C isotopic shifts • comparison of DFT simulations with observed frequencies and isotopic shifts • determine molecular structure, species and vibrational modes.

  10. Theoretical Calculations • Calculations using Gaussian 03 program suite • DFT calculations using B3LYP/6-311G(3df,3pd) functional • Calculated frequencies for the C2v singlet structure are in good agreement with Sumathi & Hendrickx. • 13C isotopic shifts calculated for comparison to experimental results.

  11. Theoretical Calculations Vibrational mode DFT Calculated (cm-1) PES Observeda (cm-1) Infrared Intensity (km/mole) 1(a1) 1291 4 C 2(a1) 866 5 C C 3(a1) 697 650 ± 30 64 4(b1) 621 12 Ti 5(b2) 1549 39 6(b2) 460 28 DFT B3LYP/6-311G(3df,3pd) predicted vibrational frequencies (cm-1) and infrared intensities (km/mole) for the fan-shaped (C2v) isomer (singlet) of TiC3. a Observation by Wang et al., JPCA 1997.

  12. Theoretical Calculations • Stretching modes of TiC3 1(a1) ~ 1291.1 cm-1 ~ 4 km/mole 2(a1) ~ 865.5 cm-1 ~ 5 km/mole 3(a1) ~ 696.7 cm-1 ~ 64 km/mole 4(b1) ~ 620.5 cm-1 ~ 12 km/mole 6(b2) ~ 459.8 cm-1 ~ 28 km/mole 5(b2) ~ 1549.4 cm-1 ~ 39 km/mole

  13. 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 Titanium rod see also WG04 on GeC5Ge (Gonzalez, previous Matrix/Condensed phase session) Ar

  14. 3.4 n5(b2) fundamental 3.4 3.4 3.4 1484.2 (a) 90% 12C/ 10% 13C rod + Ti rod, 9K C5(n4) 1446.6 Absorbance (b) 90% 12C/ 10% 13C rod + Ti rod, 24K (48-13-12-12) (48-12-12-13) (48-13-13-12) (48-12-13-13) (48-12-13-12) 1473.5 (48-13-12-13) 1450.9 1439.9 1461.4 in C spectrum (c) DFT Simulation 1430 1440 1450 1460 1470 1480 1490 Frequency (cm-1)

  15. 5(b2) fundamental Isotopomer Observed B3LYP/ 6-311G(3df,3pd) Scaled a Difference Ti-C-C-C   DFT SC Δ 48-12-12-12 1484.2 1549.4 1484.2 0.0 48-13-12-12 1473.5 1538.0 1473.3 0.2 48-12-13-12 1450.9 1513.8 1450.1 0.8 48-13-13-12 1439.9 1502.2 1439.0 0.9 48-13-12-13 1461.4 1524.9 1460.7 0.7 48-13-13-13 -- 1488.6 1426.0 -- Comparison of observed vibrational frequencies (cm-1) of the 5(b2) mode with 13C isotopomers and B3LYP/6-311G(3df,3pd) calculations. a Scaling factor of 1484.2/1549.4 = 0.95792 .

  16. 3(a1) fundamental (48-12-12-12) (48-12-13-12) 624.3 (48-13-12-12) (48-12-12-13) (48-13-13-12) (48-12-13-13) (a) 90% 12C/ 10% 13C rod + Ti rod, 16K 573.8 (48-13-12-13) (48-13-13-13) 616.8 Absorbance 608.4 (b) DFT Simulation 540 560 580 600 620 640 Frequency (cm-1)

  17. 3(a1) fundamental Isotopomer Observed B3LYP/ 6-311G(3df,3pd) Scaled a Difference Ti-C-C-C   DFT SC Δ 48-12-12-12 624.3 696.7 624.3 0.0 48-13-12-12 616.8 688.2 616.7 0.1 48-12-13-12 overlapped 696.5 624.1 -- 48-13-13-12 616.8 688.1 616.6 0.2 48-13-12-13 608.4 679.1 608.5 -0.1 48-13-13-13 -- 679.0 608.4 -- Comparison of observed vibrational frequencies (cm-1) of the 3(a1) mode with 13C isotopomers and B3LYP/6-311G(3df,3pd) calculations. a Scaling factor of 624.3/696.7 = 0.8961 .

  18. 4(b1) fundamental ? 3(a1) 624.3 (a) 90% 12C/ 10% 13C rod + Ti rod, 16K 573.8 616.8 Absorbance 608.4 (b) DFT Simulation 540 560 580 600 620 640 Frequency (cm-1)

  19. 4(b1) fundamental ? Vibrational mode DFT Calculated (cm-1) FTIR Observed (cm-1) Infrared Intensity (km/mole) 1(a1) 1291 4 C 2(a1) 866 5 C C 3(a1) 697 624.3 64 4(b1) 621 573.8? 12 Ti 5(b2) 1549 1484.2 39 6(b2) 460 28 DFT B3LYP/6-311G(3df,3pd) predicted vibrational frequencies (cm-1) and infrared intensities (km/mole) for the fan-shaped (C2v) isomer (singlet) of TiC3.

  20. 4(b1) fundamental ? • The 4 ~ 621 cm-1 mode predicted to have ~18% intensity of the 3 mode; 573.8 cm-1 has comparable intensity. • No other possible Ti-C species observed in spectrum. • Lack of isotopic shifts precludes definitive assignment to 4(b1) ~ 573.8 cm-1.

  21. Conclusions Vibrational mode DFT Calculated (cm-1) PES Observedb (cm-1) FTIR Observeda (cm-1) C C C 3(a1) 697 650 ± 30 624.3 4(b1) 621 573.8? 5(b2) 1549 1484.2 Ti • The C2v ‘fan-like’ isomer in the 1A1 state is the ground state structure of TiC3. • The following vibrational modes were observed a Uncertainty of ± 0.2 cm-1 in FTIR observed. b Observation by Wang et al., JPCA 1997.

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

  23. References • K.H. Hinkle, J.J. Keady, P.F. Bernath, Science 241, 1319 (1988). • P.F. Bernath, K.H. Hinkle, J.J. Keady, Science 244, 562 (1989). • G. von Helden, A.G.G.M. Tielens, D. van Heijnsbergen, M.A. Duncan, S. Hony, L.B.F.M. Waters, G. Meijer, Science 288, 313 (2000). • Y. Kimura, J.A. Nuth III, F.T. Ferguson, Astrophysical J. 632, L159 (2005). • B.C. Guo, K.P. Kerns, A.W. Castleman, Jr. Science 255, 1411 (1992). • S. Wei, B.C. Guo, J. Purnell, S. Buzza, A.W. Castleman, Jr. J. Phys. Chem. 96, 4166 (1992). • X.B. Wang, C.D. Ding, L.S. Wang, J. Phys. Chem. A 101, 7699 (1997). • B.V. Reddy and S.N. Khanna, J. Phys. Chem. 98, 9446 (1994). • R. Sumathi and M. Hendrickx, Chem. Phys. Lett. 287, 496 (1998). • R. Sumathi and M. Hendrickx, J. Phys. Chem. A 102, 4883 (1998). • R. Sumathi and M. Hendrickx, J. Phys. Chem. A 103, 585 (1999). • R. Sumathi and M. Hendrickx, J. Phys. Chem. A 102, 7308 (1998).

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