Radiative association cross sections are shown in Fig. 5. Comparison of the cross sections for the three species clearly demonstrates the more favorable radiative association process for PH+ and SiH+, in which the two atomic species approach along an electronically excited state potential curve from which a dipole transition is made, than for SH+, in which the entire process takes place within the ground electronic state. This difference is manifested by the two to three orders of magnitude difference in the cross sections. In addition, only the lowest energy region in the vibrational continuum of the SH+ ground state contributes to the radiative association process, so the cross section drops off rapidly for collision energies greater than 0.1 eV. The larger cross section for SiH+ relative to PH+ can be understood by comparing the square of the dipole moments of these two species in the region 2 a.u. < R < 3 a.u.
In Fig. 6 and Table 3, we present radiative
association rate coefficients
which were determined by averaging over the cross
sections with a Maxwellian velocity distribution.
The rate coefficients are fitted to the parametric form
|Si+ + H||P+ + H||S+ + H|
|Figure 8: Comparison of the P+ + H and S+ + H reactions with other P+ and S+ reactions from Millar et al. ()|
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