S. A. Bates Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129

1. Fourier Transform Infrared Isotopic Study of Novel Metal–Carbon Clusters Trapped in Ar Matrix Environments S. A. Bates Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129 Dissertation 17 April 2008

2. Outline • Motivation • Astrophysical • Metallocarbohedrenes • Research objectives • Experimental techniques • Rod fabrication • 13C isotopic substitution • New molecular identifications • CrC3 • CoC3 • AlC3,AlC3Al • CuC3

3. Outline • Future work • Tentative identifications: CrC4, AlC4Al • Unidentified VnCm candidates • Other MnCm species • Rod fabrication techniques • Summary • Acknowledgments

4. Motivation • Astrophysical • Metals observed in small molecules found in circumstellar shells and in the interstellar medium • CrO in M stars (Davis, ApJ 1947) • AlNC, NaCl in IRC+10216 (Cernicharo, A&A 1987; Ziurys et al., ApJ 2002) • NaCN, MgNC in CRL 2688 (Highberger et al., ApJ 2001) • Pure carbon chains observed in circumstellar shells (e.g. C3, C5) (Hinkle et al., Science 1988; Cernicharo et al., ApJ 2000; Bernath et al., Science 1989) • Silicon-bearing species observed in IRC+10216 include SiCN and SiC3(Apponi et al., ApJ 1999; Guélin et al., A&A 2000)

5. Motivation • Metallocarbohedrenes • Small metal carbon clusters important in understanding their formation and bonding (Guo et al., Science 1992; Guo & Castleman, Advances in Metal and Semiconductor Clusters 1994; Kooi et al., Nano Lett 2001) • TiC2, VC2 as “building blocks” for larger clusters(Wei et al., JPC 1992; Tono et al., JCP 2002) • ConCm species form from Co atoms attaching to carbon aggregates.(Tono et al., JCP 2002)

6. Research Objectives • To measure the vibrational fundamentals and 13C isotopic shifts of metal carbon species (MCn) 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 density functional theory (DFT) predictions. • 13C shifts are essential to species identification and structure determination.

7. Experimental Apparatus 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 Metal rod Ar

8. Techniques: Rod Fabrication • Sintered carbon rods (Cárdenas, 2007) • Baked for ~30 days at 2100° C • Pro: durable and provide consistent results • Con: can only fabricate 12-15 rods per year • “Soft” carbon rods • Press 12C/13C powder mixture under a pressure of ~4.5×105 GPa • Only heated overnight if impurities observed in the spectrum • Pro: can make a carbon rod in ~1 hour • Pro: consistent results if powder measured and mixed carefully • Con: can only use in 2-3 experiments • Con: currently limited to ≤50% 13C enrichment because of solid die (solution proposed in “Future Work” section)

9. Techniques: 13C Isotopic Substitution Key: metal atom 12C atom 13C atom Non-centrosymmetric molecules (e.g. MC3) Each C atom is a unique substitution site! g a b Centrosymmetric molecules (e.g. C3, MC3M) a b a a a b unique central substitution site ← → equivalent substitution sites ← → 180° rotation 180° rotation

10. New Molecules: Outline of Analysis • Previous work/background • FTIR spectra & analysis • Theoretical calculations • Conclusions

11. Periodic Table

12. Previous Work: CrCn • Previous photoelectron spectroscopy (PES) and DFT studies on MC2 and MC3 clusters (M=Sc, V–Ni) (Li & Wang, JCP 1999; Wang & Li, JCP 2000) • CrC2, metal–carbon stretch measured at 510(30) cm-1.(Li & Wang, JCP 1999) • CrC3, metal–carbon stretch measured at 560(60) cm-1. DFT investigation predicted the fanlike isomer is the lowest energy isomer. (Wang & Li, JCP 2000) Fanlike (C2v) isomer

13. Previous work: CrCn nearly isoenergetic Uncertain ground state for CrC3(Zhai et al., JCP 2004) DFT predictions for the lowest energy isomers of CrC3ˉ and CrC3 aDenotes ground state energy • Photoelectron (PE) spectra • Exhibit features consistent with both isomers. • Abundance of fanlike isomer increased with hotter source • conditions – linear isomer may be more stable.

14. 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 14 Frequency (cm-1)

15. Unidentified feature in pure 12C spectrum C3¯ (Szczepanski et al., JPCA, 1997) CrOCO (Souter & Andrews, 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 15 Frequency (cm-1)

16. 1720 1730 1740 1750 1760 1770 1780 1790 Cr rod + 15% 13C rod 1789.5 • Three remaining features • Nominal enrichment: 15% 13C • Observed 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 16 Frequency (cm-1)

17. 1789.5 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 Cr rod + 30% 13C rod Absorption Cr rod + 15% 13C rod 1777.8 1779.7 1743.4 17 Frequency (cm-1)

18. Calculations: CrC3 (1789.5) (560±60) aBoth Renner-Teller components reported. bFrequencies for fanlike structure initially published by Wang and Li, 2000.

19. Theoretical Calculations • Used density functional theory (DFT) with B3LYP functional and 6-311+G(3df) basis set in Gaussian 03 program suite. • Calculations performed for linear and fanlike structures. • Fanlikevibrational frequency calculations are in good agreement with the previous report. (Wang & Li, JCP, 2000) • 13C isotopic shift frequencies were calculated for the linear isomer.

20. Calculations: Isotopic Shift Frequenciesfor the ν1(σ) Mode of Linear CrC3 aDFT calculations scaled by a factor of 1789.5/1851.7=0.96641. bDFT calculations scaled by a factor of 1720.6/1778.8=0.96728.

21. 1720 1730 1740 1750 1760 1770 1780 1790 Cr rod + 30% 13C rod 52-12-12-12 52-13-13-13 1789.5 1720.6 52-13-13-12 52-12-12-13 1731.4 Absorption 1779.7 52-12-13-13 52-13-12-12 1733.5 52-13-12-13 52-12-13-12 1777.8 1767.1 1743.4 DFT simulation 10% 13C 21 Frequency (cm-1)

22. Conclusions: CrC3 • Linear CrC3 has been observed in its 5Π ground state. • Its ν1(σ) vibrational fundamental is assigned to 1789.5 cm-1. • This is the first measurement of a vibrational fundamental for this species. • Also first FTIR measurement of a vibrational fundamental for a transition metal–carbon cluster. • No evidence of the fanlike structure is observed – consistent with thermal behavior observed in prior photoelectron spectra. (Zhai et al., JCP 2004) Cr This work has been published: S. A. Bates, C. M. L. Rittby, and W. R. M. Graham, J. Chem. Phys. 125, 074506 (2006).

23. Periodic Table

24. Previous Work: ConCm • Previous PES and DFT studies on MC2 and MC3 clusters (M=Sc, V–Ni) (Li & Wang, JCP 1999; Wang & Li, JCP 2000) • CoC2, metal-carbon stretch measured at 540(60) cm-1.(Li & Wang, JCP 1999) • No vibrational features were resolved for CoC3 so excluded from DFT investigation – geometry undetermined.(Wang & Li, JCP 2000)

25. ν3 ν4 C3 C7 2038.9 Co rod + 12C rod 2127.8 ν7 ν7 ν6 ν9 C11 ν5 C10 C12 C9 ν3 ν6 C7 1915.8 1946.1 C5 C10 1998.0 1818.0 1894.3 2164.1 ν5 2074.9 C6 1918.2 ν8 1952.5 ν5 ν5 C11 C6ˉ C8 C9 Absorbance 1856.7 1936.7 2078.1 2071.7 12C rod 1800 1850 1900 1950 2000 2050 2100 2150 25 Frequency (cm-1)

26. ν5(u) C7 C7 1870.4 C4O C6ˉ C7 C7 Co rod + 20% 13C rod 1918.2 • Kranze et al., JCP 1996 • Bates, unpublished work • Maier et al., Angew. Chem. 1988 Absorbance 1894.3 1906.4 1922.5 1905.2 1870.8 1914.5 1886.4 1880.2 1840 1850 1860 1870 1880 1890 1900 1910 1920 26 Frequency (cm-1)

27. Co rod + 20% 13C rod • Three remaining features 1918.2 • Observed enrichment: ~9% Linear CoC3? Absorbance 1906.4 1905.2 1870.8 1840 1850 1860 1870 1880 1890 1900 1910 1920 27 Frequency (cm-1)

28. 1906.4 1905.2 1870.8 1857.8 1892.9 1906.4 1858.8 1905.2 1870.8 CHO • Milligan & Jacox, JCP 1969 Co rod + 30% 13C rod 1918.2 Single 13C shifts? Double 13C shifts? Full 13C shift (i.e. Co13C3)? Absorbance 1844.2 Co rod + 20% 13C rod 1840 1850 1860 1870 1880 1890 1900 1910 1920 28 Frequency (cm-1)

29. Calculations: CoC3 (1918.2) 0.0 kcal/mol Co +3.7 kcal/mol Co

30. Theoretical Calculations • Calculations performed for linear and fanlike structures of CoC3 • Also investigated various Co2C3 geometries that were consistent with our FTIR isotopic spectra. • No stable minimum structures with a vibrational fundamental in the right frequency region were obtained.

31. Calculations: Isotopic Shift Frequenciesfor the ν1(σ) Mode of Linear CoC3 aDFT calculations scaled by a factor of 1918.2/2013.6=0.95262. bDFT calculations scaled by a factor of 1844.2/1934.4=0.95337.

32. Co rod + 30% 13C rod 59-12-12-12 1918.2 59-13-13-13 1844.2 59-12-12-13 59-13-13-12 1906.4 1857.8 59-13-12-12 59-12-13-13 59-12-13-12 1905.2 1858.8 Absorbance 59-13-12-13 1870.8 1892.9 30% 13C B3LYP simulation 1840 1850 1860 1870 1880 1890 1900 1910 1920 32 Frequency (cm-1)

33. Conclusions: CoC3 Co • DFT calculations predict the fan and linear isomers are within a few kcal/mol and thus do not provide a clear answer for the ground state. • Linear CoC3 was observed in its 2Δground state. Its ν1(σ) C–C stretching fundamental has been identified at 1918.2 cm-1. • No evidence of fanlike isomer was observed in the FTIR spectra. • This is both the first detection of and theoretical investigation done on this molecule. This work has been published: S. A. Bates, J. A. Rhodes, C. M. L. Rittby, and W. R. M. Graham, J. Chem. Phys. 127, 064506 (2007).

34. Periodic Table

35. Previous Work: AlC3Al, AlC3 (C2v) kite (C2v) fanlike linear • No previous investigations on AlC3Al • No prior observation of AlC3 • First theoretical study: ground state is 4B1 fanlike isomer(Zheng et al., JPCA, 1999) • Subsequent theoretical investigation: (Barrientos et al., CPL, 2000) • 2B1 fanlike, 2A1 kite, and 2Π linear isomers are close in energy so any could be the ground state. • All quartet states: 24-52 kcal/mol above doublet states

36. Al rod + 12C rod ν3 C3 ν3 Al2C2 2038.9 AlnCm 605.1 ν4 ν5 C6 C7 1952.5 1894.3 528.3 1210.9 1624.0 Absorbance ν6 ν5 ν4 ν9 C9 ν7 C6 c-C6 C12 C9 Pure 12C rod 1998.0 1197.3 1694.9 1818.0 1601.0 600 800 1000 1200 1600 1800 2000 36 Frequency (cm-1)

37. Al rod + 30% 13C rod • Szczepanski et al., JPCA 1997 • Kranze et al., JCP 1995 1624.0 • Jacox, VEEL ν7 C9ˉ Cn 1613.6 ν7 C9 1584.7 Absorbance 1572.8 H2O 1561.0 1560 1570 1580 1590 1600 1610 1620 37 Frequency (cm-1)

38. Al rod + 30% 13C rod • Possible 13C shifts • Observed enrichment: ~8% 1624.0 ~16% of the 1624.0 cm-1 band – 2 equivalent C atoms? overlapped – can not accurately measure intensity ~8% of the 1624.0 cm-1 band– unique C atom? ~9% of the 1624.0 cm-1 band 1613.6 1584.7 Absorbance 1572.8 1561.0 1560 1570 1580 1590 1600 1610 1620 38 Frequency (cm-1)

39. Further Analysis • Estimate full 13C species vibrational frequency assuming harmonic approximation and little participation by Al atom(s): If the observed = 1624.0 cm-1, then = 1560.1 cm-1, which is close to the band observed at 1561.0 cm-1.

40. 1560 1570 1580 1590 1600 1610 1620 Al rod + 20% 13C rod Single 13C shifts? 1624.0 Double 13C shifts? Full 13C shift (i.e. Aln13C3)? Aln Absorbance 1613.6 1584.7 1572.8 1600.9 1561.0 Al rod + 30% 13C rod 40 Frequency (cm-1)

41. 520 530 540 • 524.0 cm-1 is a recurring feature with a line shape that is consistent with the line shapes of 525.1 and 528.3 cm-1. • 525.1 cm-1 is ~19% of 528.3 cm-1. • Observed enrichment is ~8%. • Consistent with two equivalent C atoms. • Observed bands at 528.3 and 1624.0 cm-1 maintain an intensity ratio of 528.3:1624.0 = 1.3. Al rod + 30% 13C rod 528.3 525.1 524.0 Absorbance Frequency (cm-1) 41

42. Theoretical Calculations • Used DFT with B3LYP functional and 6-311+G(3df) basis set in Gaussian 03 program suite • Calculations performed for kite and fanlike (C2v) structures of AlC3. • Good agreement with previously reported calculations (Barrientos et al., CPL 2000) • Also investigated linear AlC3Al, which is consistent with the FTIR isotopic spectra.

43. Calculations: AlC3Al and C2v Isomers of AlC3 • Observed bands at 1624.0 and 528.3 cm-1. • Intensity ratio of 528.3:1624.0 cm-1 bands is ~1.3. No vibrational frequencies predicted near observed bands. ν5 – most intense vibrational fundamental. No prediction near 528.3 cm-1. Intensity ratio ν4:ν3=1.8.

44. Calculations: Isotopic Shift Frequenciesfor the ν3(σu) and ν4(σu) Modes of Linear AlC3Al aDFT calculations scaled by a factor of 1624.0/1710.4=0.94949. bDFT calculations scaled by a factor of 528.3/541.1=0.9763.

45. 1560 1570 1580 1590 1600 1610 1620 Al rod + 20% 13C rod 27-12-12-12-27 1624.0 27-13-13-13-27 1561.0 27-12-13-12-27 1584.7 27-13-12-12-27 1613.6 27-12-13-13-27 27-13-12-13-27 Absorbance 1572.8 1600.9 20% 13C DFT simulation 45 Frequency (cm-1)

46. 520 530 540 Al rod + 30% 13C rod 27-12-12-12-27 528.3 27-13-12-12-27 525.1 27-12-13-12-27 524.0 Absorbance 30% 13C DFT simulation Frequency (cm-1) 46

47. Conclusions: AlC3Al Al ν3(σu) Al Al ν4(σu) Al • The ν3(σu)=1624.0 and ν4(σu)=528.3 cm-1 fundamentals of linear (3Σg+) AlC3Al have been observed. • This is both the first experimental and theoretical investigation on this molecule, enabling assignments of the only two IR-active vibrational fundamentals that have significant intensities. asymmetric C3 stretch with little Al participation asymmetric Al–C3 stretch

48. Al rod + 12C rod ν3 C3 ν3 Al2C2 2038.9 AlnCm 605.1 ν4 ν5 C6 ν4 C7 ν3 Al2C3 1952.5 Al2C3 1894.3 528.3 1210.9 1624.0 Absorbance ν6 ν5 ν4 ν9 C9 ν7 C6 c-C6 C12 C9 Pure 12C rod 1998.0 1197.3 1694.9 1818.0 1601.0 600 800 1000 1200 1600 1800 2000 48 Frequency (cm-1)

49. Al rod + 30% 13C rod • Single 13C shifts • Full 13C3 shift • Estimate of ν13 ≈ 1163.2 cm-1. • Lack of double 13C shifts in C3 spectrum – explains lack of double 13C shifts in this spectrum. 1210.9 Absorbance 1208.2 1185.4 1192.3 1164.0 1150 1160 1170 1180 1190 1200 1210 1220 49 Frequency (cm-1)

50. Calculations: Linear AlC3 DFT B3LYP/6-311+G(3df) predicted vibrational frequencies and IR intensities aFrequencies reported here are in good agreement with those previously published.(Barrientos et al., CPL 2000) bBoth Renner-Teller components reported.