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A&AS Supplement Series, Vol. 125, November I 1997, 543-549

Received January 13; accepted January 19, 1997

## Effective collision strengths for electron-impact
excitation of nitrogen-like MgVI

**C.A.Ramsbottom - K.L.Bell**

*Send offprint request: *C.A.Ramsbottom

Department of Applied Mathematics and Theoretical Physics,
The Queens University of Belfast, Belfast BT7 1NN, UK

### Abstract:

Effective collision strengths for electron-impact excitation of the
N-sequence ion MgVI are evaluated in the close-coupling
approximation using the multichannel R-matrix method. Twelve
LS target eigenstates are included in the expansion of the total
wavefunction, consisting of the eight *n*=2 states with configurations
2s^{2}2p^{3}, 2s2p^{4} and 2p^{5}, and the four *n*=3 states with
configuration 2s^{2}2p^{2}3s. These 12 ionic states correspond to 23
fine-structure levels, leading to a total of 253 independent
transitions. The effective collision strengths for all possible forbidden,
semi-forbidden and allowed transitions are obtained by averaging the
electron collision strengths, for a wide range of incident electron
energies, over a Maxwellian distribution of velocities. Results are
tabulated
for electron temperatures,
*T*, in the range log *T*(K) = 5.0
to

(K) = 6.1, which are the temperatures of interest for many
astrophysical applications. We conclude that the effective collision
strengths, for many of the forbidden lines considered, are significantly enhanced by
autoionizing resonances converging to the target state thresholds in the
collisional cross sections. The present calculations are the first to
include such resonance phenomena.

**keywords:** atomic data -- atomic processes

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