1. Higher Electronic Excited States of Jet-Cooled Aromatic Hydrocarbon Radicals: 1-phenylpropargyl (C9H7), 1-naphthylmethyl (C11H9), 2-naphthylmethyl (C11H9) and 9-anthracenylmethyl (C15H11) The University of Sydney School of Chemistry Gerard Dean O’Connor Klaas Nauta and Timothy W. Schmidt Molecular Photonics Group | UNSW

2. The Diffuse Interstellar Bands (DIBs) StarInterstellar MediumEarth

3. What are the carriers of the DIBs? Amorphous CarbonFullerenesCarbon Chains & Carbenes Polycyclic Aromatic Hydrocarbons (PAHs) H2CnH2Cn

4. Testing the PAH hypothesis: gas phase spectroscopy Resonantly stabilized radicals and their cations ultraviolet spectra visible spectra ultraviolet spectra h h visible spectra

5. Reilly, N.J; Kokkin, D.L; Masakazu N; Klaas N; Kable, S.H and Schmidt, T.W. (2008). "Spectroscopic Observation of the Resonance-Stabilized 1-Phenylpropargyl Radical J. Am. Chem. Soc. 130 3137-3142. DOI:10.1021/ja078342t Chalyavi, N; Troy, T.P; Nakajima, M; Gibson, B.A; Nauta, K; Sharp, R.G; Kable, S.H and Schmidt, T.W. (2011) “Excitation and emission spectra of jet-cooled naphthylmethyl radicals.” J. Phys. Chem A, 115 (27), 7959-7965, 2011. DOI: 10.1021/jp203638h O’Connor, G.D; Bacskay, G.B; Woodhouse, G.V.G; Troy T.P; Nauta, K; Schmidt, T.W. (2013) “Excitation Spectra of Large Jet-Cooled Polycyclic Aromatic Hydrocarbon Radicals: 9-Anthracenylmethyl (C15H11) and 1-Pyrenylmethyl (C17H11)” The Journal of Physical Chemistry A,117(50)13899-13907 DOI: 10.1021/jp4088833 D 1 ← D 0 excitation spectra of jet cooled aromatic radicals in the gas phase

6. Trends in Larger Resonance Stabilised Radicals 6 D 1 ← D 0 transitions weak (oscillator strength f~10 -4 ) Larger molecules D 1 ← D 0 spectra non-origin dominated

7. 1-PyMe R2C2PI Excitation Spectrum 7 13417cm -1

8. Assigned 1-PyMe Excitation Spectrum, low frequency modes 8 80% intensity of origin

9. 9 D0D0 D1D1 DnDn Transition Moments John A. Pople H.C. Longuet-Higgins Longuet-Higgins, H.; Pople, J. Proc. Phys. Soc. Lond. A 1955, 68, 591–600 f~10 -4 f >10 -2

10. Detector Source Extraction of ions Time-Of- Flight MS Resonant 2-Colour 2-Photon Ionization (R2C2PI) Ionisation continuum  +e - 

11. Detector Source Extraction of ions Time-Of- Flight MS Double Resonant Depleation Ionisation continuum d +e - D0D0 D1D1 D3D3

12. 1-phenylpropargyl calculated transitions 12 CASPT2 [6311G(d)] electrons in 9 orbital active space D 3 ← D 0 Vertical excitation energy = 33858 cm -1 Oscillator Strength = 0.016 G.V.G. Woodhouse: Undergraduate Honours Thesis, 2012

13. D 3 ← D 0 excitation spectrum of 1-phenylpropargyl radical 13 FWHM=149 cm -1 Lifetime = 36 fs Too high in energy to be a DIB

14. Matrix results of the naphthylmethyl radicals D 1 ← D 0 1&2-npme Nagy, Fulara, and Maier. J. Am. Chem. Soc. 2011, 133, 19796–19806. Calculated (by us) to be weak (CASPT2 and TD-B3LYP) We calculate both to be strong (CASPT2 and TD-B3LYP) and assign both to D 3 ← D 0 D 2 ← D 0 2-npme D 3 ← D 0 1&2-npme

15. D 3 ← D 0 excitation spectra of naphthylmethyl radicals 15 FWHM=290 cm -1 FWHM=292 cm -1 Lifetime = 18 fs Broadest DIB FWHM = 155 cm -1

16. Ionisation lifetime scan of 9-anthracenylmethyl 16

17. 17 6.42eV photon energy similar to IE

18. 18 Signal independent of lifetime

19. Trends in TD-B3LYP vertical excitation energy 19 Benzyl data from: : Porter, G; Wright, FJ; (1955) “PRIMARY PHOTOCHEMICAL PROCESSES IN AROMATIC MOLECULES.3. ABSORPTION SPECTRA OF BENZYL, ANILINO, PHENOXY AND RELATED FREE RADICALS” TRANSACTIONS OF THE FARADAY SOCIETY 51 (11) 1469-1474

20. 9-AnMe Vertical Excitation Energies B3LYP/TD-DFT 6311++G(d,p) 20 B3LYP TD-DFT [6311++G(d,p)] (corrected) – 23874(cm -1 ) M06 TD-DFT [6311++G(d,p)] (corrected) – 24229(cm -1 )

21. D 3 ← D 0 excitation spectrum of 9-anthracenylmethyl radical 21 FWHM=326 cm -1 Lifetime = 16 fs

22. Trends in TD-B3LYP vertical excitation energy 22

23. Trend, the energy gap law in action 23

24. Trends in observed in polycyclic aromatic hydrocarbon resonance stabilised radicals (PAH RSRs) 24 odd-alternate hydrocarbon radicals D 1 ← D 0 extremely weak (f ≈10 -4 ), with most intensity going to higher energy transition transitions with intensity greater than f ≈10 -2 have been calculated and observed Strong visible transitions of PAH RSRs will be significantly broader then any observed DIBs As these are the transitions most likely to be observed, PAH RSR can be largely dismissed as potential DIB carriers

25. Acknowledgements 25 Supervisor: Prof Tim Schmidt Co-Workers: Gabrielle Woodhouse Prof Scott Kable Dr Klaas Nauta Dr Tyler Troy Laser Spectroscopy Group UNSW Molecular photonics group