L.B. "Zhao

T." Kato

National Institute for Fusion Science (NIFS-Repository)

§11. Quantum-Mechanical Interference in Photorecombi nation of Sc3+ Zhao, L.B. (Beijing Univ. Aeron. Astron.), Kato, T. Most of atomic data of photorecombination processes used in plasmas is based on independent calculations for radiative and dielectronic recombination (RR and DR). DR-RR interference is not considered in general. Es-pecially, it is taken for granted to omit the interference effects in recombination for low- or medium-Z ions. Re-cently Gorczyca et al1 predicted a unusually large DR-RR interference effect in recombination of S c3+ theoret-ically. However, the experimental search for the strong DR-RR interference effect failed2 (see Fig. 1), and the comparison displays the several peaks observed are not given by Gorczyca et al. We have carried out both nonperturbative and per-turbative calculations for the e + Sc3+ photorecombina-tion. The nonperturbative method is based on the rig-orous continuum-bound transition theory and the close-coupling R-matrix approach. The perturbative evalua-tion is a treatment including DR, RR, and their interfer-ence. The rate coefficients are presented in Fig. 2. Our calculations showed that the appearance of the several · experimental resonance peaks, which were not predicted by Gorczyca et al in the LS-coupling scheme, is attributed to relativistic effects. For example, the LS coupling cal-culations do not give the resonance 3p5 3d2 (3 F] 2 D 0 at about 16.9 e V due to limitation of the angular momen-tum and parity conservation. Only when spin-orbit inter-action is taken into account, can corresponding recombi-nation happen. It should be pointed out that in general, the resonances that stem from the relativistic effect are of small Auger widths if the atomic number Z is not large. However, a very narrow resonance may play an impor-tant role in recombination. This is because whether a resonance is significant depends not only on Auger and radiative widths of the resonances themselves but also on the Auger and radiative widths of the dominant res-onances. Therefore, it is unsafe to omit relativistic ef-fects for recombination of low- or medium-Z ions with no check. We noticed that the interference effect between the res-onance 3p5 3cf2 (3 F] 2 F and the background, predicted by Gorczyca et al1 , is reproduced by our calculation in the LS coupling scheme. But when relativistic effects are considered, the two new peaks on the left side of the 3p5 3cf2[3 F] 2 F appear, as shown in the experiment. Thus the interference effect is masked on the left side of the resonance by the adjacent resonances. On the other side of the resonance, the results calculated are much higher than the experiment. We calculated RR, DR, and inter-ference cross sections in perturbation theory, and found that just the RR should be responsible for the great dis-crepancy. A possible reason is that the RR cross section is greatly overestimated because of the difficulty to describe the many-electron systems exactly. We tried to employ the 1/10 times the RR cross sections to evaluate the in-terference and total cross sections including DR, RR and interference terms. A very good agreement with the ex-periment has been shown (here the result is not given). Even so, further experimental and theoretical studies are required. For example, considering the high resolution in photoionization experiments, we call for an observation of photoionization of Sc2+ in the 3p6 3d 2 D state to ex-amine the recombination measurement and calculations. ~~ I DR of Ar-like Sc3+ I 0 !:. " c «) 0 E 8 3 (,) ~ ~ c 2 0 :;; c :0 1 E 0 (,) CD a:: 10 11 12 13 14 15 16 17 18 Relative energy (eV) Fig. 1 The measured rate coefficients for Sc3+ compared with the calculation of Gorczyca et al1 (full line). 9 .-----------------------------~ -with damping -- without damping ,-.... 8 II) ""s 7 (.) b 6 c II) 5 i5 C1) ·c:~ 4 c.;:: ...... C1) 0 3 (.) C1) ~ 2 ...... 0:: ~ 1 0 8 10 12 14 16 18 Relative energy ( e V) Fig. 2 The calculated rate coefficients for S c3+ Reference 1) T. W. Gorczyca et al, Phys. Rev. A 56, 4742 (1997). 2) S. Schippers et al, Phys. Rev. A. (to be submitted) 383 

Quantum-Mechanical Interference in Photorecombination of Sc3+

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