Question about spectrometer data

[DariusP]

Hello, I want to ask about this picture. This is a one bit of plasma spectrum from copper plate. Does anyone know what those romanic numbers (I, II, III) mean or what those numbers in [ ] mean? Also why am I seeing multiple element names on a single peak? I am so confused...
P.S. The x-axis is wavelength, and y-axis is intensity.

 

[phyzguy]

The Roman numerals are used to denote the ionization state of the atoms where the transition is occurring. I means a neutral atom. II means an atom with one electron removed. III means an atom with two electrons removed, and so on. So O-IV is an oxygen atom with 3 electrons removed. N-III is a nitrogen atom with two electrons removed, and so forth. There are multiple lines on those peaks because the wavelengths are so close together. The line may be anyone of those lines, or (more likely) a combination. I'm not sure what the numbers in brackets refer to, but I think they denote the strength of the lines.