THE PHOTODISSOCIATION OF SIH+ IN INTERSTELLAR CLOUDS AND STELLAR ATMOSPHERES

Using a combination of both theoretical and experimentally derived pot ential curves and dipole transition moments, photodissociation cross s ections have been calculated for the SiH+ molecule. From the v '' = 0 level of the X (1) Sigma(+) ground state, with a threshold energy of 3 .256 eV, dissociation occurs through the A (1) Pi state producing Si(3p P-2) and H atoms. For energies above 9.45 eV, photodissociation th rough the 2 (1) Pi state yields excited neutral Si (3p(2 1)D) and prot ons. Excited Si+ (3s3p(2 2)D) and H atoms are produced above 10.08 eV by dissociation through 3 (1) Sigma(+) and 3 (1) Pi. The 2 (1) Sigma() and 4 (1) Pi states are found to be negligible dissociation channels . Photodissociation cross sections as a function of energy and photodi ssociation rates in the interstellar radiation held for both diffuse a nd dense molecular clouds are presented. Photodissociation cross secti ons from LTE distributions of vibrational and rotational levels of the X (1) Sigma(+) state to the A (1) Pi state are also obtained for temp eratures between 1000 and 9000 K. Their possible contribution to a mis sing opacity source in the near-ultraviolet spectra of red giant stars is discussed.