What do the Roman Numerals mean in Spectroscopic Data?

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Discussion Overview

The discussion centers around the interpretation of Roman numerals in spectroscopic data, specifically regarding the ionization states of elements such as Argon. Participants explore the meanings of Ar I, Ar II, and Ar III, and question the representation of neutral and negatively ionized species in this context.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant asks for clarification on the meaning of Ar I, Ar II, and Ar III, specifically questioning whether Ar II refers to an Ar- ion or an Ar+ ion.
  • Another participant provides a summary indicating that Roman numerals denote the level of ionization, with I representing neutral atoms, II for singly ionized atoms, and so forth.
  • A participant humorously references a saying about the pronunciation of "unionised," highlighting a cultural distinction.
  • Another participant acknowledges the provided answer but raises a further question about the notation for negatively ionized species, such as Cl-.
  • A repeated humorous remark about the pronunciation of "unionised" is made, suggesting a light-hearted tone in the discussion.

Areas of Agreement / Disagreement

Participants generally agree on the basic meanings of the Roman numerals in terms of ionization levels, but there is no consensus on how negatively ionized species are represented or if they fit within this framework.

Contextual Notes

The discussion does not address the representation of neutral or negatively ionized species in detail, leaving assumptions about their notation unresolved.

arthurhaythornthwait
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TL;DR
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...
 
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arthurhaythornthwait said:
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.
 
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Who was it that said "you can tell the difference between a chemist and an economist by how they pronounce 'unionised'"?
 
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Thanks for this. It answers the question, but as always raises the other - what about negatively ionised species (Cl-, etc.) ?
 
mjc123 said:
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.
 
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