Shapes and sizes of hydrocarbons in space

Samenvatting

Polycyclic aromatic hydrocarbons (PAHs) are the most abundant complex molecules in space. They contain 10-20% of the total cosmic carbon, play an active role in the evolution of interstellar gas, and are possible pre-biotic roots of life. Their near infrared (NIR) emission features have been observed in the interstellar medium of many galaxies and constitute a powerful probe to analyse regions of star and planet formation. Nevertheless, present models linking observed emission features to individual PAHs lack molecular specificity and are largely un-validated. Gas-phase measurements are restricted to a few, small PAHs (10-16 carbon atoms). Astronomically sized PAHs (predicted sizes ~50-100 carbon atoms) are confined to matrix-isolation spectroscopy measurements that are subject to systematic uncertainties. Calculations are therefore mandatorily calibrated against scarce and uncertain laboratory data. In addition, anharmonicity of the NIR vibrational modes is thought to play an important role in the observed emission profiles but no laboratory data exists to extract the mode and molecule specific information contained within the observations. Recent quantum chemical calculations point to the possible molecule dependence of low-lying vibrational modes involving the carbon skeleton. No laboratory data exists to confirm and validate these far infrared (FIR) predictions. This proposal presents new approaches to measure large PAHs in the gas phase, identify their low-lying vibrational modes, and characterise anharmonic behaviour. (a) The FELIX Facility in Nijmegen is one of two instruments worldwide to study the FIR response of large PAHs directly. (b) The high-resolution laser facility in Amsterdam provides new opportunities to investigate NIR vibrational modes of gas-phase PAHs, including their anharmonicity, in detail. The results can validate quantum chemical predictions, build an improved PAH database, and allow for interpretation of FIR spectra from space instruments such as HIFI and shape future missions searching for planet and star formation.

Kenmerken

Projectnummer

723.014.007

Hoofdaanvrager

Dr. ir. A. Petrignani-Taube

Verbonden aan

Universiteit Leiden, Faculteit der Wiskunde en Natuurwetenschappen, Sterrewacht Leiden

Uitvoerders

N.B. Niet Bekend en Niet Gebruiken, Dr. ir. A. Petrignani-Taube, Dr. W.G. Roeterdink, S.D. Wiersma MSc

Looptijd

01/03/2016 tot 13/11/2019