  Binary neutron star mergers are the first confirmed site of element
nucleosynthesis by the rapid neutron-capture process (r-process). The kilonova
AT2017gfo is the only electromagnetic counterpart of a neutron star merger
spectroscopically observed. We analyse the entire spectral sequence of
AT2017gfo (from merger to +10.4 days) and identify seven emission-like
features. We confirm that the prominent 1.08 um feature can be explained by the
Sr II near-infrared triplet evolving from a P-Cygni profile through to pure
emission. We calculate the expected strength of the [Sr II] doublet and show
that its absence requires highly clumped ejecta. Near-infrared features at 1.58
and 2.07 um emerge after three days and become more prominent as the spectra
evolve. We model these as optically thick P-Cygni profiles and alternatively as
pure emission features (with FWHM = 35600 +/- 6600 km/s), and favour the latter
interpretation. The profile of the strong 2.07 um emission feature is best
reproduced with two lines, centred at 2.059 and 2.135 um. We search for
candidate ions for all prominent features in the spectra. Strong, permitted
transitions of La III, Ce III, Gd III, Ra II and Ac I are plausible candidates
for the emission features. If any of these features are produced by
intrinsically weak, forbidden transitions, we highlight candidate ions spanning
the three r-process peaks. The second r-process peak elements Te and I have
plausible matches to multiple features. We highlight the need for more detailed
and quantitative atomic line transition data.
