Deep echelle spectrophotometry of S 311, a Galactic H II region located outside the solar circle

We present echelle spectrophotometry of the Galactic H it region S 311. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 310010 400 A range. We have measured the intensities of 263 emission lines; 178 are permitted lines of H-0, D-0 (deuterium), He-0, C-0, C+, N-0, N+, O-0, O+, S+, Si-0, Si+, Ar-0 and Fe-0; some of them are produced by recombination and others mainly by fluorescence. Physical conditions have been derived using different continuum- and line-intensity ratios. We have derived He+, C++ and O++ ionic abundances from pure recombination lines as well as abundances from collisionally excited lines for a large number of ions of different elements. We have obtained consistent estimations of t(2) applying different methods. We have found that the temperature fluctuations paradigm is consistent with the T-e(He I) versus T-e(H I) relation for H II regions, in contrast with what has been found for planetary nebulae. We report the detection of deuterium Balmer lines up to DS in the blue wings of the hydrogen lines, whose excitation mechanism seems to be continuum fluorescence.