The influence of coronene super-hydrogenation on the coronene-graphite interaction.

Anders W Skov,Mie Andersen,Bjarke Jørgensen,Liv Hornekær,John D Thrower,Bjørk Hammer

doi:10.1063/1.4966259

Abstract

The changes in the strength of the interaction between the polycyclic aromatic hydrocarbon, coronene, and graphite as a function of the degree of super-hydrogenation of the coronene molecule are investigated using temperature programmed desorption. A decrease in binding energy is observed for increasing degrees of super-hydrogenation, from 1.78 eV with no additional hydrogenation to 1.43 eV for the fully super-hydrogenated molecule. Density functional theory calculations using the optB88-vdW functional suggest that the decrease in binding energy is mostly due to an increased buckling of the molecule rather than the associated decrease in the number of π-electrons.

Highlights

IntroductionPolycyclic aromatic hydrocarbons (PAHs) may play a key role as catalysts for interstellar chemical complexity, as well as for the formation of larger carbon clusters and carbonaceous grains
We present temperature programmed desorption (TPD) measurements that reveal a significant decrease in binding energy with increasing super-deuteration, from 1.78 eV for coronene with no excess deuterium atoms (C24H12) to 1.43 eV for fully super-deuterated coronene (C12D36), where all available sites have been deuterated and the H-atoms present on the pristine coronene molecule have been replaced by D-atoms
After exposing the coronene monolayer to atomic D, temperature programmed desorption (TPD) measurements were performed by heating the sample with a linear temperature ramp (β) of 1 K s−1, with desorbing molecules being detected with a quadrupole mass spectrometer (QMS; Extrel CMS LLC) scanning in the range from 290 to 365 amu e−1

Summary

Introduction

PAHs may play a key role as catalysts for interstellar chemical complexity, as well as for the formation of larger carbon clusters and carbonaceous grains.. Observations of photodissociation regions (PDRs) have shown a correlation between the abundance of PAHs and the formation rate of molecular hydrogen.. Observations of photodissociation regions (PDRs) have shown a correlation between the abundance of PAHs and the formation rate of molecular hydrogen.6,17 Based on this it has been suggested that PAH molecules may act as efficient catalysts for H2 formation.. Based on this it has been suggested that PAH molecules may act as efficient catalysts for H2 formation.6 This hypothesis has been supported by theoretical calculations and experimental measurements probing both neutral and cationic PAH species, reflecting that the PAH charge state of particular interstellar regions is observed to be dependent on the UV flux.

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Conclusion