The J \ 0 ] J@ \ 0 radiative transitions, usually viewed as allowed through two-photon decay, may also be induced by the hyperÐne (HPF) interaction in atoms or ions having a nonzero nuclear spin. We compute new and review existing decay rates for the transitions in ions of the Be nsnp 3PJ o ] ns2 1S J{/0 (n \ 2) and Mg (n \ 3) isoelectronic sequences. The HPF induced decay rates for the J \ 0 ] J@ \ 0 transitions are many orders of magnitude larger than those for the competing two-photon processes, and when present are typically 1 or 2 orders of magnitude smaller than the decay rates of the magnetic quadrupole (J \ 2 ] J@ \ 0) transitions for these ions. Several HPF induced transitions are potentially of astrophysical interest in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe, and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission-line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV and EUV solar and nebular data in light of these new results and suggest possible applications for future study. We could not Ðnd evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing interesting upper limits. For the planetary nebula SMC N2, we derive an upper limit of 0.1 for 13C/12C from Goddard High-Resolution Spectrograph data obtained by Clegg. It is likely that more stringent limits could be obtained using newer data with higher sensitivities in a variety of objects.
The spectrum of scandium was recorded in the infrared region using a high resolution Fourier transform spectrometer and a hollow-cathode discharge. Hyperfine structures of the lines connecting the 3d24s and 3d4s4p level systems of S C ~~I were observed between 4000 and 5000cm-I. The structures were not completely resolved but the individual line contributions to the complex profiles were simulated using the 3d24s 4F, hyperfine structure constants previously measured with a high precision by laser techniques. We investigate the possibility of extracting the hyperfine constants of the 3d4s4p levels from a least-squares fit of the line profiles, assuming a Doppler lineshape and theoretical relative intensities. New results are presented for 12 levels.
High resolution profiles of neutral vanadium lines have been recorded in the infrared region (1800-9000 cm-1) by Fourier transform spectroscopy. 106 transitions showing resolved or partially resolved hyperfine profiles have been analysed. An investigation of these structures has allowed the deduction of magnetic dipole constants for 101 levels. For 69 levels the results obtained are new. The results of the present work have been compared with the few data previously published in the literature and they are generally in good agreement.
We are investigating the hyper6ne quenching of 1s2p Po for the three heliumlike ions F +, Na +, and Al + in the multicon6gurational Hartree-Fock-Breit-Pauli scheme. The configuration expansions are generated with the active-space method and are increased in a systematic way, allowing the convergence of the calculated parameters to be studied. A
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