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We present deep spectroscopy of three Galactic planetary nebulae (PNe) withlarge abundance discrepancy factors (ADFs): NGC6153, M1-42 and Hf2-2. Thespectra were obtained with VLT/UVES and cover the whole optical range(3040-11,000 A) with a spectral resolution of ~20,000. For all three PNe,several hundred emission lines were detected and identified, with more than 70per cent of them as permitted lines. Most of these permitted lines are excitedby recombination. Numerous weak optical recombination lines (ORLs) of O II, CII, N II and Ne II were detected in the spectra and accurate fluxes measured.Line flux tables were compiled and ready for use by the community of nebularastrophysics. These ORLs were critically analyzed using the effectiverecombination coefficients recently calculated for the optical recombinationspectrum of N II and O II under the physical conditions of photoionized gaseousnebulae. Plasma diagnostics based on the heavy element ORLs were carried outusing the new atomic data. Elemental abundances derived from the ORLs weresystematically higher than those derived from the collisionally excited lines(CELs) by a factor of ~10, 22 and 80 for NGC6153, M1-42 and Hf2-2,respectively. The electron temperatures derived from the heavy element ORLs aresystematically lower than those derived from the CELs. These ORL versus CELabundance and temperature discrepancies, previously observed in the three PNethrough deep spectroscopy with medium to low spectral resolution, are thusconfirmed by our analysis of the deep echelle spectra using the new atomicdata.

Very Large Telescope deep echelle spectroscopy of Galactic planetary nebulae NGC 6153, M 1-42 and Hf 2-2