O. PIRALI, J. OOMENS, N. POLFER FOM Rijnhuizen, 3439MN Nieuwegein, The Netherlands Y. UENO, R. MABOUDIAN Department of Chemical Engineering, U.C. Berkeley, USA P. MAY, J. FILIK School of Chemistry, University of Bristol, UK J. DAHL, S. LIU, B. CARLSON Molecular Diamond Technologies, Chevron Technology Ventures, Richmond, USA Progress on the infrared spectroscopy of diamondoids. Astrophysical Application Columbus 2006/ Spectroscopy of diamondoids

Presentation of the molecules Structure: diamond-like carbon cages sp 3 hybridised terminated with hydrogen atoms Spectroscopy:  Adamantane, diamantane : IR spectra and calculations  First spectroscopic characterization for the higher diamondoids Spectroscopy of diamondoids Synthesis:  3 smaller can be synthesized  Higher : isolated from petroleum (Dahl et al., Science, 299, 96, 2003)

Guillois et al, ApJ, 521, L133, 1999 HD Lack in the IR spectroscopy of these molecules Possible presence in ices: 50 C atoms, < 1 nm Allamandola et al., Science 260, 64, 1993 Astrophysical relevance Spectroscopy of diamondoids Extraction from meteorites (Lewis, Nature 18, 550, 1987) / Mean size: 2 nm 3.53  m 3.43  m 3.47  m Only two sources HD ELIAS 1 Assignment in the ISM : > 50 nm

Spectroscopy of diamondoids Laboratory results Gas phase spectroscopy for the three first ones FT thermal emission in the 3  m region Solid state spectroscopy for 7 higher diamondoids (Attenuated total reflection spectroscopy) DFT calculations B3LYP, D95 SF=0.988 SF=0.947

Symmetry D 3d 162 Vibrational modes A u and E u symmetry infrared allowed Example of Hexamantane Spectroscopy of diamondoids Analysis of the spectra 1450CH 2 scissor 1300CH bend 1050CH 2 rock / CC stretch Region (cm -1 ) Vibration 2900CH stretch <1000 skeleton deformation

Similarities between the spectra Regions of interest for astrophysics: 3  m 6.8  m 7.7  m Below 1000 cm -1 ? Analysis of the spectra Spectroscopy of diamondoids

Addition of all the solid state spectra 2840 cm -1 / 3.52  m CH stretch 2875 cm -1 / 3.47  m CH / CH 2 asymmetric 2905 cm -1 / 3.44  m CH 2 symmetric  Intense transitions  Region of interest for astrophysics  General assignment consistent for all the molecules Spectroscopy of diamondoids Analysis in the 3  m region

 3.53  m : larger molecules shift toward the lowest frequencies for the CH stretch. Intensity increases  3.43  m : tetrahedral symmetry (adamantane and pentamantane). Spectroscopy of diamondoids Dependence of the spectra with size and structure / astrophysical interest Support ISM assignement TdTd D 3d C 2v

 3.53  m : larger molecules shift toward the lowest frequencies for the CH stretch.  3.43  m : tetrahedral symmetry (adamantane and pentamantane).  3.43  m : no shifts of CH 2 band towards the higher frequencies. Presence of methyl groups ?  3.47  m observed in ices. Presence of small diamondoids ?  Correlation with 6.8  m ? Spectroscopy of diamondoids Dependence of the spectra with size and structure / astrophysical interest Support ISM assignement Questions

Observation of the first spectra IR of these molecules Calculations supporting the global assignment of the spectra Possible detailed assignment in the stretching mode region The ISM features assigned to diamondoids at 3.43 and 3.53  m correspond to our observations. Spectroscopy of diamondoids Conclusion  Comparison with more astrophysical data  Correlation with the 6.8  m band observe in ice and ISM  Calculations on larger molecules Perspectives