Identification of new gold lines in the 350 to 1000 nm spectral region using laser produced plasmas

TL;DR

This study uses laser-produced plasma spectroscopy to discover 54 new spectral lines of gold in the 350-1000 nm range, aiding astrophysical research on neutron star mergers.

Contribution

It introduces a novel application of laser-produced plasma spectroscopy for identifying new spectral lines of gold relevant to astrophysics.

Findings

Identified 54 previously unknown gold spectral lines.

Provisionally matched 21 lines to theoretical atomic models.

Demonstrated the method's applicability from UV to IR wavelengths.

Abstract

We present results from a pilot study, using a laser-produced plasma, to identify new lines in the 350 to 1000 nm spectral region for the r-process element gold (Au), of relevance to studies of neutron star mergers. This was achieved via optical-IR spectroscopy of a laser-produced Au plasma, with an Au target of high purity (99.95 %) and a low vacuum pressure to remove any air contamination from the experimental spectra. Our data were recorded with a spectrometer of 750 mm focal length and 1200 lines mm-1 grating, yielding a resolution of 0.04 nm. We find 54 lines not previously identified and which are not due to the impurities (principally copper (Cu) and silver (Ag)) in our Au sample. Of these 54 lines, we provisionally match 21 strong transitions to theoretical results from collisional-radiative models that include energy levels derived from atomic structure calculations up to the 6s level. Some of the remaining 33 unidentified lines in our spectra are also strong and may be due to transitions involving energy levels which are higher-lying than those in our plasma models. Nevertheless, our experiments demonstrate that laser-produced plasmas are well suited to the identification of transitions in r-process elements, with the method applicable to spectra ranging from UV to IR wavelengths.