Spectroscopy and Photochemistry of the Astrochemical Molecules SiCP and AlCP

Abstract Through characterization of the electronic excited-state topology, linear-SiCP is predicted to be photostable in the UV region, whereas linear-AlCP is predicted to undergo photodissociation to form Al+CP products after absorption of light in the 200–250 nm range, representing a catalytic process for freeing aluminum molecules from a solid dust grain. Both SiCP and AlCP are predicted to have electronic transitions with large absorption cross sections (∼10 –17 cm 2 ) and to undergo fluorescence from bound excited states. The total electronic absorption spectrum is provided to inform electronic spectroscopy experiments. Silicon (SiC) and aluminum (Al 2 O 3 ) dust grains are ubiquitous in the interstellar medium, and are especially prominent in the circumstellar envelopes of evolved stars such as VY CMa and IRC+10216. These regions of space are hotbeds for chemical activity, where reactions can occur on the surfaces of these dust grains to form new species. One such reaction that has been theorized involves the CP radical interacting with dust grain surfaces to produce the triatomic molecules SiCP and AlCP. To motivate and facilitate experimental and observational searches for AlCP, its ground-state spectroscopic properties (rotational and vibrational) have been investigated. The small permanent dipole moment (∼0.1 D) is expected to make radioastronomical observation difficult, although experimental detection may be feasible if a sufficiently large molecular number density can be achieved.