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FTIR Observation and DFT Study of the AlC 3 and AlC 3 Al Linear Chains Trapped in Solid Ar

FTIR Observation and DFT Study of the AlC 3 and AlC 3 Al Linear Chains Trapped in Solid Ar. S.A. Bates, C.M.L. Rittby, and W.R.M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129 International Symposium on Molecular Spectroscopy

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FTIR Observation and DFT Study of the AlC 3 and AlC 3 Al Linear Chains Trapped in Solid Ar

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  1. FTIR Observation and DFT Study of the AlC3 and AlC3Al Linear Chains Trapped in Solid Ar S.A. Bates, C.M.L. Rittby, and W.R.M. Graham Department of Physics and Astronomy Texas Christian University Fort Worth, TX 76129 International Symposium on Molecular Spectroscopy 63rd Meeting -- June 16-20, 2008 The Ohio State University

  2. Astrophysical Interest • Aluminum observed in small molecules found in circumstellar shells and in the interstellar medium • AlNC, AlCl, AlF in IRC+10216 (Ziurys et al., Proc. Nat. Acad. Sci. 2006) • Carbon chains observed in circumstellar shells • C3, C5 (Hinkle et al.Science 1988; Cernicharo et al., ApJ 2000; Bernath et al., Science 1989)

  3. (C2v) fanlike 2B1 linear 2Π (C2v) kite 2A1 Previous Studies AlC3 • DFT and MP2 calculations (Zheng et al., J. Phys. Chem. A, 1999) • Ground state: 4B1 fanlike isomer • Subsequent DFT, MP2, CCSD(T) study (Barrientos et al., Chem. Phys. Lett., 2000) • Ground state: 2B1 fanlike, and 2Π linear isomers nearly isoenergetic • 2A1 kite at +6-8 kcal/mol • Quartet states +24-52 kcal/mol • No experimental work AlC3Al • No previous investigations

  4. Experimental Apparatus 1064 nm pulsed Nd-YAGlaser 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 (500 - 3500 cm-1) • 0.2 cm-1 resolution To pump ~10-7Torr To pump 10-3Torr Carbon rod Al rod Ar Bates and Kinzer

  5. AlnCm absorptions Al rod + 12C rod 12C rod C3 ν3 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 1998.0 1197.3 1694.9 1818.0 1601.0 600 800 1000 1200 1600 1800 2000 Frequency (cm-1)

  6. C9ˉSzczepanski et al., JPCA 1997 • C9Kranze et al., JCP 1995 1624.0 Al rod + 30% 13C rod ν7 C9ˉ Cn 1613.6 ν7 C9 1584.7 Absorbance 1572.8 H2O 1561.0 1560 1570 1580 1590 1600 1610 1620 Frequency (cm-1)

  7. 13C Isotopic shifts Aln Al rod + 20% 13C rod 1560 1570 1580 1590 1600 1610 1620 1624.0 Int. ~8 and 16% of 1624 cm-1--single13C shifts? Harmonic estimate ν(13C) ≈ 1560.1 cm-1 Double 13C shifts? 1613.6 1584.7 1572.8 1600.9 1561.0 Absorbance Al rod + 30% 13C rod Frequency (cm-1)

  8. 520 530 540 Al rod + 30% 13C rod • Int. 525.1 cm-1 is ~19% of 528.3 cm-1. • Observed enrichment ~8% • Consistent with two equivalent C • atoms • Observed bands at 528.3 and • 1624.0 cm-1 maintain a constant • intensity ratio ≈ 1.3. 528.3 525.1 524.0 Absorbance Frequency (cm-1)

  9. 1.97Å Al Al 1.29 DFT B3LYP/6-311+G(3df) Calculations: (3Σg+) AlC3Al • Observed bands at 1624.0 and • 528.3 cm-1 • Observed intensity ratio of • 528.3:1624.0 cm-1band ~1.3 • Predicted intensity ratio • ν4:ν3 ~1.8

  10. Mode Isotopomer Observed B3LYP/ 6-311+G(3df) Scaled Difference Al-C-C-C-Al νobs νDFT νsc Δν=νobs-νsc ν3(σu) 27-12-12-12-27 1624.0 1710.4 …a … 27-13-12-12-27 1613.6 1699.0 1613.2 0.4 27-12-13-12-27 1584.7 1668.6 1584.3 0.4 27-13-13-13-27 1561.0 1643.2 1560.1 0.9 27-12-13-13-27 1572.8 1657.0 1573.3 -0.5 27-13-12-13-27 1600.9 1685.8 1600.6 0.3 ν4(σu) 27-12-12-12-27 528.3 541.1 …b … 27-13-12-12-27 525.1 537.1 524.4 0.7 27-12-13-12-27 524.0 535.8 523.1 0.9 Comparison between observed and calculated shifts for the ν3(σu) and ν4(σu) modes of linear AlC3Al aDFT calculations scaled by 1624.0/1710.4=0.94949. bDFT calculations scaled by 528.3/541.1=0.9763.

  11. 13C isotopic shifts for ν4(σu) mode of AlC3Al 1560 1570 1580 1590 1600 1610 1620 27-12-12-12-27 27-13-13-13-27 1624.0 1561.0 27-12-13-12-27 Al rod + 20% 13C rod 1584.7 27-13-12-12-27 1613.6 27-12-13-13-27 27-13-12-13-27 Absorbance 1600.9 1572.8 20% 13C DFT simulation Frequency (cm-1)

  12. Al rod + 30% 13C rod 30% 13C DFT simulation 520 530 540 13C isotopic shifts for ν3(σu) mode of AlC3Al 27-12-12-12-27 528.3 27-13-12-12-27 525.1 27-12-13-12-27 524.0 Absorbance Frequency (cm-1)

  13. AlC3Al Conclusions • Two vibrational fundamentals of linear (3Σg+) AlC3Al have been observed. • First experimental or theoretical investigation of AlC3Al molecule, enabling the assignment of the only two IR-active fundamentals with significant intensity. ν3 (σu)=1624.0 cm-1 asymmetric C3 stretch with little Al participation ν4(σu)=528.3 cm-1 asymmetric Al–C3 stretch

  14. AlnCm absorptions C3 ν3 ν3 Al2C2 2038.9 AlnCm 605.1 ν4 ν5 C6 ν4 AlC3Al C7 ν3 AlC3Al 1952.5 1894.3 528.3 1210.9 1624.0 Absorbance ν6 Al rod + 12C rod ν5 ν4 ν9 C9 ν7 C6 c-C6 C12 C9 1998.0 1197.3 1694.9 1818.0 12C rod 1601.0 600 800 1000 1200 1600 1800 2000 Frequency (cm-1)

  15. 13C Isotopic shifts Al rod + 30% 13C rod • Single 13C shifts • Full 13C3 shift estimated at ν13C ≈ 1163.2 cm-1 • Lack of double 13C substitution consistent with C3 • spectrum – non-randomization of isotopes 1210.9 1208.2 1185.4 1192.3 1164.0 Absorbance 1150 1160 1170 1180 1190 1200 1210 1220 Frequency (cm-1)

  16. 2.02Å 1.33 Al 1.27 DFT B3LYP/ 6-311+G(3df) calculations: AlC3 • Observed band at 1210.9 cm-1 DFT predicted vibrational frequencies and IR intensities aFrequencies in good agreement with Barrientos et al., Chem. Phys. Lett. 2000 bBoth Renner-Teller components reported

  17. Comparison between observed andcalculated shifts for the ν2(σ) mode of linear AlC3 aDFT calculations scaled by a factor of 1210.9/1245.0=0.97261

  18. 30% 13C DFT simulation 27-12-12-12 13C isotopic shifts forν1(σ)mode of AlC3 1210.9 27-12-13-12 Al rod + 12C rod 1208.2 27-12-12-13 27-13-12-12 27-13-13-13 1185.4 1192.3 1164.0 Absorbance Double shifts not observed 1150 1160 1170 1180 1190 1200 1210 1220 Frequency (cm-1)

  19. Al AlC3 Conclusions • DFT calculations do not provide a clear answer for the ground state. • Linear AlC3 observed in its 2Πground state. • ν2(σ) C–C stretching fundamental = 1210.9 cm-1. • This is the first observation and measurement of a vibrational fundamental for this species. This work is scheduled for publication in J. Chem. Phys.

  20. Acknowledgments • Funding • Welch Foundation • TCU Research and Creative Activities Fund • W.M. Keck Foundation • Texas Space Grant Consortium Fellowship (Sarah Bates)

  21. References • L.M. Ziurys, Proc. Nat. Acad. Sci. 103, 12274 (2006). • K.H. Hinkle, J.J. Keady, and P.F. Bernath, Science 241, 1319 (1988). • P.F. Bernath, K.H. Hinkle, and J.J. Keady, Science 244, 562 (1989). • X. Zheng, Z. Wang, and A. Tang, J. Phys. Chem. A 103, 9275 (1999). • C. Barrientos, P. Redondo, and A. Largo, Chem. Phys. Lett. 320, 481 (2000). • J. Szczepanski, S. Eckern, and M. Vala, J. Phys. Chem. A 101, 1847 (1997). • M.E. Jacox, NIST Vibrational and Electronic Energy Levels Database (http://webbook.nist.gov/chemistry) • R.H. Kranze, P.A. Withey, C.M.L. Rittby, and W.R.M. Graham, J. Chem. Phys. 103, 6841 (1995). • S.A. Bates, C.M.L. Rittby, and W.R.M. Graham, J. Chem. Phys., in preparation.

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