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Binary neutron star mergers are the first confirmed site of elementnucleosynthesis by the rapid neutron-capture process (r-process). The kilonovaAT2017gfo is the only electromagnetic counterpart of a neutron star mergerspectroscopically observed. We analyse the entire spectral sequence ofAT2017gfo (from merger to +10.4 days) and identify seven emission-likefeatures. We confirm that the prominent 1.08 um feature can be explained by theSr II near-infrared triplet evolving from a P-Cygni profile through to pureemission. We calculate the expected strength of the [Sr II] doublet and showthat its absence requires highly clumped ejecta. Near-infrared features at 1.58and 2.07 um emerge after three days and become more prominent as the spectraevolve. We model these as optically thick P-Cygni profiles and alternatively aspure emission features (with FWHM = 35600 +/- 6600 km/s), and favour the latterinterpretation. The profile of the strong 2.07 um emission feature is bestreproduced with two lines, centred at 2.059 and 2.135 um. We search forcandidate ions for all prominent features in the spectra. Strong, permittedtransitions of La III, Ce III, Gd III, Ra II and Ac I are plausible candidatesfor the emission features. If any of these features are produced byintrinsically weak, forbidden transitions, we highlight candidate ions spanningthe three r-process peaks. The second r-process peak elements Te and I haveplausible matches to multiple features. We highlight the need for more detailedand quantitative atomic line transition data.

Modelling the spectra of the kilonova AT2017gfo -- II: Beyond the photospheric epochs