The Photodissociation of SiH+ in Interstellar Clouds and Stellar Atmospheres

Using a combination of both theoretical and experimentally derived potential curves and dipole transition moments, photodissociation cross sections have been calculated for the SiH⁺ molecule. From the v" = 0 level of the X ¹Σ⁺ ground state, with a threshold energy of 3.256 eV, dissociation occurs through the A ¹Π state producing Si⁺ (3p ²P) and H atoms. For energies above 9.45 eV, photodissociation through the 2 ¹Π state yields excited neutral Si (3p^{2 1}D) and protons. Excited Si⁺ (3s3p^{2 2}D) and H atoms are produced above 10.08 eV by dissociation through 3 ¹Σ⁺ and 3 ¹Π. The 2 ¹Σ⁺ and 4 ¹Π states are found to be negligible dissociation channels. Photodissociation cross sections as a function of energy and photodissociation rates in the interstellar radiation field for both diffuse and dense molecular clouds are presented. Photodissociation cross sections from LTE distributions of vibrational and rotational levels of the X ¹Σ⁺ state to the A ¹Π state are also obtained for temperatures between 1000 and 9000 K. Their possible contribution to a missing opacity source in the near-ultraviolet spectra of red giant stars is discussed.