ElectronConfiguration

An electron configuration is a list of orbital / occupancy pairs, plus an optional term symbol for total angular momentum state.

Fields

Field	Type	Description
orbitals	Array of [orbital, occ] pairs	Pairs like ["1s", "2"]
term_symbol	TermSymbol (optional)	Multiplicity / letter / J value

The TermSymbol struct has :multiplicity, :letter, :j_value fields, all strings.

Diagram

       ┌─────────────────────────────────────┐
       │       ElectronConfiguration         │
       │                                     │
       │   orbitals[0]  ("1s", "2")          │
       │   orbitals[1]  ("2s", "2")          │
       │   orbitals[2]  ("2p", "6")          │
       │   ...                               │
       │                                     │
       │   term_symbol  (optional)           │
       │     ├── multiplicity                │
       │     ├── letter                      │
       │     └── j_value                     │
       └─────────────────────────────────────┘

Grammar production

electron_config := (orbital "^" occupancy){2,}
orbital := digits [spdfgh]
occupancy := digits

Two or more orbital^occupancy pairs in sequence.

Term symbols (deferred)

Term symbols (^3P_2) are first-class in the model but the v1 parser doesn’t promote them from text. Use embedded math for now:

`^3P_2`

${\displaystyle ^3P_2}$

The model is ready for the grammar extension in v0.3+.

Formatter behaviour

Formatter	Each orbital
MathML	<msup><mi>1s</mi><mn>2</mn></msup> joined with non-breaking spaces
Text	1s^2 2s^2 2p^6
HTML	1s<sup>2</sup> joined with spaces
LaTeX	\ce{1s^2 2s^2 2p^6}
SVG	Linear ASCII

Round-trip

AsciiChem.parse("1s^2 2s^2").to_text                                # => "1s^2 2s^2"
AsciiChem.parse("1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10").to_text     # => same (zinc)

What’s not here

• Box notation (orbital diagrams with up/down arrows) — needs SVG, deferred to 2D structural support (TODO 18).
• Hund’s rule validation — out of scope for the parser; the linter could add a HundCheck.
• Excited-state vs ground-state markers — needs syntax design.