What do the Roman Numerals mean in Spectroscopic Data?

[arthurhaythornthwait]

TL;DR Summary

What exactly does each roman numeral mean?

A basic question. Looking at the NIST spectroscopic data, what exactly is, for example, Ar I vs Ar II vs Ar III? If Ar I is unionised Argon, then is Ar II an Ar- ion or an Ar+ ion? (and whichever way around it works, how do we denote the opposite ionisation? If they are all ionized, is there such a thing as Ar 0 (plain argon)? I'm not aware that the romans understood zero or negative numbers...

 

[berkeman]

TL;DR Summary: What exactly does each roman numeral mean?

Welcome to PF. A quick Google search on Roman numerals in spectroscopy gives this as the first hit:

http://legacy.ifa.hawaii.edu/newsletters/article.cfm?a=517

Spectral lines are designated according to the level of ionization by adding a Roman numeral to the symbol of the chemical element. Neutral atoms are denoted by I, singly ionized atoms (those missing one electron) with II, and so on. For example, Fe IX represents an iron atom that is missing eight electrons.

 

[mjc123]

Who was it that said "you can tell the difference between a chemist and an economist by how they pronounce 'unionised'"?

 

[arthurhaythornthwait]

Thanks for this. It answers the question, but as always raises the other - what about negatively ionised species (Cl-, etc.) ?

 

[arthurhaythornthwait]

Who was it that said "you can tell the difference between a chemist and an economist by how they pronounce 'unionised'"?

A chef might say you're spelling it wrong.