Molecule formation processes involving second-row elements are of considerable interest, as searches for new molecular species in a variety of interstellar and circumstellar environments continue. Phosphorus-, sulfur- and silicon-containing molecules have been observed and identified, but no diatomic hydrides of these elements, or their associated ions, have been detected to date (Millar & Hobbs ; Magnani & Salzer , ). Other diatomic hydrides, such as OH (which is chemically similar to SH), and diatomic hydride ions, such as CH+ (which is chemically similar to SiH+) have been observed in considerable abundance. Among the formation mechanisms for SiH+, PH+, and SH+, the process of radiative association should be included.
Using ab initio molecular potential energy curves and transition moments, we have carried out calculations for the radiative association of X+ (X = Si, P, or S) with H:
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