HIGH RESOLUTION SPECTROSCOPY OF THE CARBON CAGE ADAMANTANE C10H16 Vincent BOUDON Laboratoire Interdisciplinaire Carnot de Bourgogne – UMR 5209 CNRS-Université de Bourgogne, 9 Av. A. Savary, BP 47870, F-21078 DIJON, France Olivier PIRALI*, Didier BALCON, Michel VERVLOET Ligne AILES – Synchrotron SOLEIL, L’Orme des Merisiers, F-91192, GIF-SUR-YVETTE, France * and ISMO, CNRS, Bat 210 Université Paris Sud, Orsay, France Jos OOMENS Inst. Plasma Phys. Rijnhuizen, FOM, NL-3439 MN Nieuwegein, Netherlands

Contents The adamantane molecule The spectra Analysis of line positions Conclusion

I. The adamantane molecule

Why adamantane ? The simplest diamondoid molecule, composed of a single tetrahedral carbon cage. Diamond-like molecules have unique structures and properties (stability, hadrness, rigidity, optical transparency, …). Presence of diamond-like materials (which are more stable than graphite) is suspected in different astrophysical objects. Intense emission features around 3.43 and 3.53 μm in the circumstellar shell of some Herbig objects to CH stretching modes of diamond-like molecules. Such an identification remains hypothetical, however. Detailed spectroscopic studies of such molecules should be performed.

A tetrahedral cage Calculated structure of C10H16 using the B3LYP DFT with the 6-31G(d,p) basis set. There are 72 vibrational modes, including 11 F2 IR active modes. The ground state rotational constant is estimated to: B0 ≈ 1.6747 GHz ≈ 0.0558 cm-1

II. The spectra

AILES beamline at SOLEIL High Resolution Absorption Spectroscopy in the Far-IR Interferometer Synchrotron beam entrance Multipass cell : Max = 200m Bolometer detectors Maximum spectral resolution = 0.001 cm-1 Spectral range= 7-1000 cm-1

Overview of the vibrational spectrum

The high-resolution spectra Different pressures have been used, because of band intensities ranging from a few tens to several hundreds of km.mol-1. Spectral range / cm-1 Gaz pressure / mb Spectral resolution / cm-1 Continuum source Scan time / h 600 – 4500 0.02 0.001 Globar 40 33 – 600 0.07 Synchrotron 31 1000 – 2000 0.006 30 Optical path (White cell) : 151.75 m

III. Analysis of line positions

Effective tensorial Hamiltonian Polyad structure P0 P1 P2 Systematic tensorial development Coupled rovibrational basis Effective Hamiltonian and vibrational extrapolation

Overview of the n30 band

Detail in the n30 band

Detail in the n28 band

Detail in the n27 band

Detail in the n26 band

Rovibrational levles of the n26 band

Effective Hamiltonian parameters At present, all the analyzed bands were considered as isolated. Assignments could be realized up to high J values. Many effective Hamiltonian parameters could be determined.

IV. Conclusion

A lot of work left The present analyses are still preliminary. All bands were taken as isolated, but there may be interactions to consider. A band is observed near 950 cm-1, just below ν27, which may be an interacting E level (probably ν11, observed in Raman). ν27 ν11 ? ν25 and ν24 could not yet be analyzed and may be perturbed. Other bands may be recorded.

Spherical Top Data System The STDS database Spherical Top Data System www.icb.cnrs.fr/OMR/SMA/SHTDS • Molecular parameter database • Calculation and analysis programs • XTDS : Java interface