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FTIR MATRIX AND DFT STUDY OF THE VIBRATIONAL SPECTRUM OF CYCLIC ScC 3

FTIR MATRIX AND DFT STUDY OF THE VIBRATIONAL SPECTRUM OF CYCLIC ScC 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. 63 rd International Symposium on Molecular Spectroscopy The Ohio State University

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FTIR MATRIX AND DFT STUDY OF THE VIBRATIONAL SPECTRUM OF CYCLIC ScC 3

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  1. FTIR MATRIX AND DFT STUDY OF THE VIBRATIONAL SPECTRUM OF CYCLIC ScC3 R.E. Kinzer, Jr., C. M. L. Rittby, W. R. M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129 63rd International Symposium on Molecular Spectroscopy The Ohio State University 16-20 June 2008

  2. Motivation: Astrophysical • Transition-metal carbide clusters may potentially be observed in circumstellar shells. • Over 140 molecules have been observed in circumstellar shells or the interstellar medium. (Cologne Database, April 2008) • Carbon clusters are observed in circumstellar shells. • C3, C4, C5 • Molecules bearing carbon chains are observed. • CCCN, HC4N, C5N, HC9N

  3. Motivation: Astrophysical • Numerous metal-bearing molecules have been observed in circumstellar shells. • MgCN, AlNC, FeO • Transition-metals have been observed in F- to M-type circumstellar shells. • Mn, Fe, Cd • Molecules bearing transition-metals observed in spectra of M-type stars. • TiO, VO, FeH, CrH • Few studies have measured transition-metal carbide spectra.

  4. Motivation: Metallocarbohedrenes • Building blocks: M8C12+ (M = Ti, V, Zr, Hf, Nb) metallocarbohedrene (“metcar”). • Other large metal-carbide molecules have been observed; MC2 seems to serve as a building block. • How do smaller transition-metal carbides (ScC2, ScC3, 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.

  5. Previous Experimental ScCn Research • Photoelectron spectroscopy (PES) and density functional theory (DFT) study of MC2 and MC3 (M = Sc, V, Cr, Mn, Fe, Co, Ni) clusters.(Li and Wang, 1999/2000) • PES results • ScC2: 670 ± 40 cm-1 metal-carbon stretch • ScC3: 560 ± 30 cm-1 ground state metal-carbon stretch 600 ± 50 cm-1excited electronic state (+10 kcal/mol) • DFT-B3LYP results • ScC3 structure is fanlike • ScC3 ground electronic state is doublet

  6. Previous Theoretical Research • All investigations predicted fanlike ground state. • DFT investigations (Li and Wang 2000; Roszak 2002; Redondo 2006) • fanlike 2A2 electronic ground state • fanlike 4B1 state ~6-10 kcal/mol higher • Linear geometries > 20 kcal/mol above ground state • CASSCF - CASPT2 (Hendrickx and Clima 2004) • fanlike 2A2 ground state (4B1, +9 kcal/mol) • MRSDCI, MRSDCI+Q (Roszak et al. 2002) • fanlike 4B1 ground state (2A2, +10-11 kcal/mol)

  7. DFT Theoretical Simulations • Simulations using GAUSSIAN 03 suite • B3LYP functional with 6-311G(3df, 3pd) basis set • Fanlike geometries, 2A2 and 4B1 electronic states modeled • 13C isotopic shift spectra simulated for both electronic states for comparison to measured isotopic shifts • Determined molecular structure, species and vibrational modes

  8. DFT Simulations 560 ± 30 cm-1 (PES) 1.32 Å 1.31 Å Cβ Fanlike (C2v) Cα Cα 2.19 2.05 2.15 2.05 Sc

  9. 2A2 Vibrational Modes Sc Sc a)ν1(a1) b)ν2(a1) c)ν3(a1) 1256 cm-1 4 km/mol 792 cm-1 2 km/mol 601 cm-1 80 km/mol d)ν4(b1) e)ν5(b2) f)ν6(b2) (as seen in plane of molecule) 415 cm-1 70 km/mol 1523 cm-1 9 km/mol 368 cm-1 23 km/mol

  10. 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 Scandium rod Carbon rod Ar

  11. Experimental Results • Scandium carbide candidates found by comparison of Sc and 12C spectra to 12C spectra. • 3 candidate Sc-C absorptions observed which maintained consistent intensity ratios • The ν3(σu)=2038.9 cm-1 fundamental of C3 dominated spectra, suggesting the three candidates are absorptions of a C3 bearing molecule. • Similar frequencies (1484.2 and 624.3 cm-1) measured for fanlike TiC3, so fanlike ScC3 is a good candidate. 560 ± 30 cm-1 (PES)

  12. ν5(b2) 1478.0 • 75 / 25 ~ 12C/13C, • after annealing at 30 K 12-12-12 ● ~ C5 shifts Shift intensities behave like C3 spectrum 13-12-12 12-13-12 1468.2 13-13-12 1442.4 13-13-13 13-12-13 1432.4 C5 ν4 Absorbance 1421.3 1457.3 ● ● b) 2A2 simulation c) 4B1 simulation 1410 1420 1430 1440 1450 1460 1470 1480 Frequency (cm-1)

  13. ν5(b2) fundamental a The predicted 2A2 shifts scaled by a factor of 1478.0/1522.7 = 0.97064. b The predicted 4B1 shifts scaled by a factor of 1478.0/1517.1 = 0.97423.

  14. ν5(b2) fundamental • Measured at 1478.0 cm-1 • Asymmetric carbon stretching mode • Isotopic spectra confirm fanlike geometry • Simulated isotopic spectra for both 2A2 and 4B1 states match measured data well • ν5(b2) data do not allow the elimination of either state

  15. ν3(a1) • 75 / 25 ~ 12C/13C, • after annealing at 30 K 557.0 550.0 543.0 X Absorbance • Only two isotopic shifts. • Similar pattern observed for fanlike TiC3… 520 540 560 580 Frequency (cm-1)

  16. Cyclic TiC3: 3(a1) fundamental presented 2006 Astronomical Species & Processes (WH10) 12-12-12 12-13-12 624.3 13-12-12 13-13-12 Absorbance ν3(a1) TiC3 13-12-13 13-13-13 616.8 (a) 90% 12C/ 10% 13C rod + Ti rod, 16K 608.4 (b) DFT Simulation 540 560 580 600 620 640 Frequency (cm-1)

  17. 2A2 4B1 • 75 / 25 ~ 12C/13C, • after annealing at 30 K 557.0 13-12-12 13-13-12 12-12-12 12-13-12 550.0 13-12-13 13-13-13 543.0 X Absorbance b) 4B1 simulation c) 2A2simulation 520 540 560 580 Frequency (cm-1)

  18. ν3(a1)fundamental OL = overlapped a The predicted 2A2 shifts scaled by a factor of 557.0/601.2 = 0.92648. b The predicted 4B1 shifts scaled by a factor of 557.0/531.7 = 1.018. c Shift is overlapped by the fundamental at 557.0 cm-1 (Sc-12-12-12). d Shift is overlapped by the isotopic shift at 543.0 cm-1 (Sc-13-12-13).

  19. ν3(a1) fundamental • Measured at 557.0 cm-1 • significant overlap of isotopic shifts (similar to TiC3) • most intense ScC3 absorption • Symmetric metal-carbon stretch • Shift pattern confirms 2A2 ground state and not 4B1 • Confirms the 560 ± 30 cm-1 vibration measured in previous PES study

  20. ν1(a1) • 75 / 25 ~ 12C/13C, • after annealing at 30 K C6 ν5 1190.7 ● ~ C6 shifts 12-12-12 12-13-12 13-12-12 1182.8 13-13-12 1171.6 ● ● 1163.0 ● ● ● Absorbance b) 2A2 simulation c) 4B1 simulation 1150 1160 1170 1180 1190 1200 Frequency (cm-1)

  21. ν1(a1) fundamental a The predicted 2A2 shifts scaled by a factor of 1190.7/1256.4 = 0.94771. b The predicted 4B1 shifts scaled by a factor of 1190.7/1277.3 = 0.93220.

  22. ν1(a1) fundamental • Measured at 1190.7 cm-1 • three isotopic shifts measured • consistent intensity ratio to other ScC3 bands • Symmetric carbon stretching mode • Shift spectra match 2A2 and 4B1 states well • ν3(a1) shift spectra eliminated quartet state!

  23. Conclusions • Cyclic ScC3 (fanlike, C2v) in 2A2 electronic ground state observed • FTIR 13C isotopic shift spectra • DFT simulated isotopic spectra • Three vibrational fundamentals measured This research is to be submitted to J. Chem. Phys.

  24. Acknowledgements • The Welch Foundation • TCU Research and Creative Activities Fund • W.M. Keck Foundation for the Bomem spectrometer

  25. References ScmCn Experimental / Theoretical papers • X. Li and L. S. Wang, J. Chem. Phys. 111, 8389 (1999). • L. S. Wang and X. Li, J. Chem. Phys. 112, 3602 (2000). • V. M. Rayón, P. Redondo, C. Barrientos, A. Largo, Chem. Eur. J. 12, 6963 (2006). • P. Redondo, C. Barrientos, and A. Largo, J. Phys. Chem. A 110, 4057 (2006). • S. Roszak, D. Majumdar, and K. Balasubramanian, J. Chem. Phys. 116, 10238 (2002). • M. F. A. Hendrickx and S. Clima, Chem. Phys. Lett. 388, 284 (2004). • P. Redondo, C. Barrientos, and A. Largo, J. Phys. Chem. A, 109, 8594 (2005). Additional Transition-Metal Carbide Papers • R. E. Kinzer, Jr., C. M. L. Rittby and W. R. M. Graham, J. Chem. Phys. 125, 74513 (2006). • S. A. Bates, C. M. L. Rittby and W. R. M. Graham, J. Chem. Phys. 125, 74506 (2006). • S. A. Bates, C. M. L. Rittby and W. R. M. Graham, J. Chem. Phys. 127, 64506 (2007). • R. E. Kinzer, Jr., C. M. L. Rittby and W. R. M. Graham, J. Chem. Phys., 128, 64312 (2008). • S. A. Bates, C. M. L. Rittby and W. R. M. Graham, J. Chem. Phys., in press.

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