Photodissociation of small carbonaceous molecules of astrophysical interest

TL;DR

This study provides detailed quantum chemical calculations of excitation energies and oscillator strengths for small carbonaceous molecules relevant to astrophysics, enabling estimation of their photodissociation rates under interstellar conditions.

Contribution

It offers the first ab initio data on excitation energies and oscillator strengths for several small carbon molecules, improving models of their photodissociation in space.

Findings

Identified new excited states with large oscillator strengths below ionization potentials.

Calculated upper limits on photodissociation rates for multiple molecules.

Provided data to better interpret astronomical observations of carbonaceous molecules.

Abstract

Astronomical observations have shown that small carbonaceous molecules can persist in interstellar clouds exposed to intense ultraviolet radiation. Current astrochemical models lack quantitative information on photodissociation rates in order to interpret these data. We here present ab initio multi-reference configuration-interaction calculations of the vertical excitation energies, transition dipole moments and oscillator strengths for a number of astrophysically relevant molecules: C3, C4, C2H, l- and c-C3H, l- and c-C3H2, HC3H, l-C4H and l-C5H. Highly excited states up to the 9'th root of each symmetry are computed, and several new states with large oscillator strengths are found below the ionization potentials. These data are used to calculate upper limits on photodissociation rates in the unattenuated interstellar radiation field by assuming that all absorptions above the dissociation limit lead to dissociation.