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We investigate the possibility of diagnosing the degree of departure from theMaxwellian distribution using single-ion spectra originating in astrophysicalplasmas in collisional ionization equilibrium. New atomic data for excitationof Fe IX-XIII are integrated under the assumption of a kappa-distribution ofelectron energies. Diagnostic methods using lines of a single ion formed at anywavelength are explored. Such methods minimize uncertainties from theionization and recombination rates, as well as the possible presence ofnon-equilibrium ionization. Approximations to the collision strengths are alsoinvestigated. The calculated intensities of most of the Fe IX-XIII EUV linesshow consistent behaviour with kappa at constant temperature. Intensities ofthese lines decrease with kappa, with the vast majority of ratios of stronglines showing little or no sensitivity to kappa. Several of the line ratios,especially involving temperature-sensitive lines, show a sensitivity to kappathat is of the order of several tens of per cent, or, in the case of Fe IX, upto a factor of two. Forbidden lines in the near-ultraviolet, visible, orinfrared parts of the spectrum are an exception, with smaller intensity changesor even a reverse behaviour with kappa. The most conspicuous example is the FeX 6378A red line, whose intensity incerases with kappa. This line is apotentially strong indicator of departures from the Maxwellian distribution. Wefind it possible to perform density diagnostics independently of kappa, withmany Fe XI-XIII line ratios showing strong density-sensitivity and negligiblesensitivity to kappa and temperature. We also tested different averaging of thecollision strengths. It is found that averaging over 0.01 interval inlog(E/Ryd) is sufficient to produce accurate distribution-averaged collisionstrengths at temperatures of the ion formation in ionization equilibrium.

Signatures of the non-Maxwellian $\kappa$-distributions in optically thin line spectra \subtitle{I. Theory and synthetic Fe IX--XIII spectra}