### Install PyValem from source

Source: https://github.com/xnx/pyvalem/blob/master/README.rst

Alternative installation methods for local source directories.

```bash
# either
python setup.py install

# or
python3 -m pip install .
```

--------------------------------

### Install PyValem via pip

Source: https://github.com/xnx/pyvalem/blob/master/README.rst

Standard installation command for the PyValem package.

```bash
python3 -m pip install pyvalem
```

--------------------------------

### Install PyValem

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/introduction.md

Installation commands for the PyValem package via pip or from source.

```bash
python3 -m pip install pyvalem
```

```bash
# either
python setup.py install

# or
python3 -m pip install .
```

--------------------------------

### Install pyvalem in editable mode

Source: https://github.com/xnx/pyvalem/blob/master/README.rst

Install the package with development dependencies in a virtual environment.

```bash
pip install -e .[dev]
```

```zsh
pip install -e .'[dev]'
```

--------------------------------

### Retrieve HTML Representation of AtomicConfiguration

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Access the html attribute to get a formatted string representation of the configuration.

```pycon
>>> print(c2.html)
[Ne]3s<sup>2</sup>3d<sup>10</sup>
```

--------------------------------

### Instantiate Reaction Objects

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/reaction.md

Create Reaction instances using reactant and product strings separated by valid reaction arrows.

```pycon
>>> from pyvalem.reaction import Reaction
>>> r1 = Reaction('CO + O2 → CO2 + O')
>>> r2 = Reaction('CO v=1 + O2 J=2;X(3SIGMA-g) → CO2 + O')
>>> r3 = Reaction('HCl + hv -> H+ + Cl + e-')
>>> r4 = Reaction('C6H5OH + 7O2 → 6CO2 + 3H2O')
```

--------------------------------

### Use the Formula class

Source: https://github.com/xnx/pyvalem/blob/master/README.rst

Instantiate chemical formulas to access properties like charge, mass, and formatted strings.

```pycon
>>> from pyvalem.formula import Formula

>>> # neutral formulas:
>>> Formula('C2H5OH')
C2H5OH

>>> # isotopes:
>>> Formula('(14C)')
(14C)

>>> # ions
>>> [Formula('H3O+'), Formula('(1H)(2H)+'), Formula('Co(H2O)6+2')]
[H3O+, (1H)(2H)+, Co(H2O)6+2]

>>> # special species
>>> [Formula('e-'), Formula('hv')]
[e-, hν]

>>> # formula attributes:
>>> Formula('Ar+2').charge
2

>>> Formula('H2(18O)').html
'H<sub>2</sub><sup>18</sup>O'

>>> print(Formula('H2(18O)').latex)
\mathrm{H}_{2}{}^{18}\mathrm{O}

>>> Formula('(235U)').mass
235.04392819
```

--------------------------------

### Instantiating KeyValuePair objects

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Create KeyValuePair instances by passing a string in the 'key=value' format. Whitespace is not permitted within the string.

```pycon
>>> from pyvalem.states import KeyValuePair
>>> kv1 = KeyValuePair('n=1')
>>> kv2 = KeyValuePair('|M|=2')
>>> kv3 = KeyValuePair('sym=anti')
```

--------------------------------

### Instantiate StatefulSpecies

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/stateful_species.md

Create StatefulSpecies objects using a formula string followed by whitespace-delimited or punctuation-delimited quantum states.

```pycon
>>> from pyvalem.stateful_species import StatefulSpecies
>>> ss1 = StatefulSpecies('HCl v=2 J=0')
>>> ss2 = StatefulSpecies('NCO v2+3v1;J=10.5;a(2Σ-g)')
>>> ss3 = StatefulSpecies('Ar+ 1s2.2s2.2p5, 2P_3/2')
>>> ss4 = StatefulSpecies('CrH 1sigma2.2sigma1.1pi4.3sigma1; 6SIGMA+')
```

--------------------------------

### Handle configuration labels

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Use lowercase prefixes to distinguish terms with identical S and L values based on parity and energy order.

```pycon
>>> from pyvalem.states import AtomicTermSymbol
>>> a0 = AtomicTermSymbol('a5D')
>>> a1 = AtomicTermSymbol('b5D')
>>> a2 = AtomicTermSymbol('z3Po')
>>> a3 = AtomicTermSymbol('y3Po')
```

--------------------------------

### Instantiate AtomicConfiguration

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Create atomic configuration objects using orbital specifiers separated by periods.

```pycon
>>> from pyvalem.states import AtomicConfiguration
>>> c0 = AtomicConfiguration('1s2')
>>> c1 = AtomicConfiguration('1s2.2s2.2p6')
>>> c2 = AtomicConfiguration('1s2.2s2.2p6.3s2.3d10')
```

--------------------------------

### Instantiate DiatomicMolecularConfiguration

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Create configuration objects using orbital strings with symmetry labels and occupancy numbers.

```pycon
>>> from pyvalem.states import DiatomicMolecularConfiguration
>>> c1 = DiatomicMolecularConfiguration('1σ')
>>> c2 = DiatomicMolecularConfiguration('1σu2')
>>> c3 = DiatomicMolecularConfiguration('1piu4.1pig3')
>>> c4 = DiatomicMolecularConfiguration('1σg2.1σu2.2σg2.2σu2.1πu4.3σg2')
```

--------------------------------

### Instantiate MolecularTermSymbol

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Demonstrates creating MolecularTermSymbol instances with various term symbol formats.

```pycon
>>> from pyvalem.states import MolecularTermSymbol
>>> c1 = MolecularTermSymbol('1Σ-')
>>> c2 = MolecularTermSymbol('1SIGMA-')
>>> c3 = MolecularTermSymbol('3Σ+g')
>>> c4 = MolecularTermSymbol('3SIGMA+g')
>>> c5 = MolecularTermSymbol('b(4Π_-3/2)')
>>> c6 = MolecularTermSymbol("A'(1A1g_0)")
>>> c7 = MolecularTermSymbol('A(1A")')
```

--------------------------------

### Instantiate VibrationalState

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Create vibrational state objects for diatomic or polyatomic molecules using string representations of quanta.

```pycon
>>> from pyvalem.states import VibrationalState
>>> v0 = VibrationalState('v=0')
>>> v1 = VibrationalState('v=*')
>>> v2 = VibrationalState('3v2+v3')
>>> v3 = VibrationalState('ν1+ν2')
>>> v4 = VibrationalState('2v1+3v4')
>>> v5 = VibrationalState('2ν1+1ν2+ν3')
```

--------------------------------

### Execute project tests

Source: https://github.com/xnx/pyvalem/blob/master/README.rst

Run the test suite from the project root directory using pytest or tox.

```bash
# either
pytest

# or
tox
```

--------------------------------

### Initialize AtomicTermSymbol objects

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Create instances of AtomicTermSymbol using standard LS-coupling notation strings.

```pycon
>>> from pyvalem.states import AtomicTermSymbol
>>> a0 = AtomicTermSymbol('3P_1')
>>> a1 = AtomicTermSymbol('4D')
>>> a2 = AtomicTermSymbol('2Po_1/2')
```

--------------------------------

### DiatomicMolecularConfiguration(config_string)

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Constructor for creating a new diatomic molecular configuration object from a string representation.

```APIDOC
## DiatomicMolecularConfiguration(config_string)

### Description
Instantiates a new configuration object representing the electronic state of a diatomic molecule. The input string consists of a sequence of numbered molecular orbitals separated by periods.

### Parameters
- **config_string** (string) - Required - A string representing the molecular orbitals (e.g., '1σg2.1σu2').

### Attributes
- **html** (string) - An HTML representation of the configuration with proper subscript and superscript formatting.

### Errors
- **DiatomicMolecularConfigurationError** - Raised if an orbital is filled with too many electrons or if an orbital is repeated in the configuration string.
```

--------------------------------

### Instantiate and Access RotationalState

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Create rotational state objects using J quantum number strings and access the parsed numerical value.

```pycon
>>> from pyvalem.states import RotationalState
>>> r0 = RotationalState('J=0')
>>> r1 = RotationalState('J=3/2')
>>> r2 = RotationalState('J=1.5')
>>> r3 = RotationalState('J=*')
>>> print(r1.J)
1.5
```

--------------------------------

### Use the Reaction class

Source: https://github.com/xnx/pyvalem/blob/master/README.rst

Define chemical reactions and collisional processes, which automatically validate charge and stoichiometry.

```pycon
>>> from pyvalem.reaction import Reaction
>>> reaction = Reaction('He+2 + H -> He+ 3p1 + H+ + hv')
>>> reaction
He+2 + H → He+ 3p + H+ + hν

>>> reaction.html
'He<sup>2+</sup> + H → He<sup>+</sup> 3p + H<sup>+</sup> + hν'

>>> print(reaction.latex)
\mathrm{He}^{2+} + \mathrm{H} \rightarrow \mathrm{He}^{+} \; 3p + \mathrm{H}^{+} + h\nu
```

--------------------------------

### Access HTML representation

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Retrieve the HTML-formatted string for a configuration object using the html attribute.

```pycon
>>> print(c3.html)
1π<sub>u</sub><sup>4</sup>.1π<sub>g</sub><sup>3</sup>

>>> print(c4.html)
1σ<sub>g</sub><sup>2</sup>.1σ<sub>u</sub><sup>2</sup>.2σ<sub>g</sub><sup>2</sup>.2σ<sub>u</sub><sup>2</sup>.1π<sub>u</sub><sup>4</sup>.3σ<sub>g</sub><sup>2</sup>
```

--------------------------------

### Manage Stateful Species

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/introduction.md

Work with species that include quantum state information, supporting atomic configurations and term symbols.

```pycon
>>> from pyvalem.stateful_species import StatefulSpecies

>>> stateful_species = StatefulSpecies('Ne+ 1s2.2s2.2p5; 2P_1/2')
>>> stateful_species.formula
Ne+

>>> type(stateful_species.formula)
<class 'pyvalem.formula.Formula'>

>>> stateful_species.states
[1s2.2s2.2p5, 2P_1/2]

>>> state1, state2 = stateful_species.states
>>> type(state1)
<class 'pyvalem.states.atomic_configuration.AtomicConfiguration'>

>>> state1.orbitals
[1s2, 2s2, 2p5]

>>> type(state2)
<class 'pyvalem.states.atomic_term_symbol.AtomicTermSymbol'>

>>> state2.L, state2.J
(1, 0.5)
```

```pycon
>>> print(stateful_species.latex)
\mathrm{Ne}^{+} \; 1s^{2}2s^{2}2p^{5} \; {}^{2}\mathrm{P}_{1/2}

>>> StatefulSpecies('(52Cr)(1H) 1sigma2.2sigma1.1delta2.1pi2; 6SIGMA+; v=0; J=2').html
'<sup>52</sup>Cr<sup>1</sup>H 1σ<sup>2</sup>.2σ<sup>1</sup>.1δ<sup>2</sup>.1π<sup>2</sup> <sup>6</sup>Σ<sup>+</sup> v=0 J=2'
```

--------------------------------

### Instantiate GenericExcitedState

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Create generic excited state objects using asterisk notation or numeric prefixes.

```pycon
>>> from pyvalem.states import GenericExcitedState
>>> x0 = GenericExcitedState('*')
>>> x1 = GenericExcitedState('***')
>>> x2 = GenericExcitedState('5*')
```

--------------------------------

### Use Noble Gas Shorthand in AtomicConfiguration

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Specify closed-shell configurations using noble gas symbols in square brackets.

```pycon
>>> c2 =  AtomicConfiguration('[Ne].3s2.3d10')
```

--------------------------------

### Generate Stoichiometric Formulas

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/formula.md

Output the stoichiometric formula in either increasing atomic number order or alphabetical order.

```pycon
>>> lys.stoichiometric_formula()
'H14C6N2O2'

>>> lys.stoichiometric_formula('alphabetical')
'C6H14N2O2'
```

--------------------------------

### Calculate Formula Properties

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/formula.md

Retrieve atomic counts, relative molecular mass, charge, and stoichiometric dictionaries from a Formula object.

```pycon
>>> f = Formula('CO3-2')
>>> f.natoms
4

>>> round(f.rmm, 3)  # relative molecular mass
60.008

>>> f.charge
-2

>>> dict(f.atom_stoich)
{'C': 1, 'O': 3}

>>> lys = Formula('(NH3+)(CH2)4CH(NH2)CO2-')
>>> lys.natoms
24

>>> round(lys.rmm, 2)
146.19

>>> lys.charge
0
```

--------------------------------

### Generate Formula Representations

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/formula.md

Access HTML, LaTeX, and URL-safe slug representations of a chemical formula.

```pycon
>>> from pyvalem.formula import Formula
>>> f = Formula("Co(H2O)6+2")
>>> print(f.formula)  # or simply print(f)
Co(H2O)6+2

>>> print(f.html)
Co(H<sub>2</sub>O)<sub>6</sub><sup>2+</sup>

>>> print(f.latex)
\mathrm{Co}(\mathrm{H}_{2}\mathrm{O})_{6}^{2+}

>>> print(f.slug)
Co-_l_H2O_r_6_p2
```

--------------------------------

### Compare StatefulSpecies Equality

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/stateful_species.md

Two StatefulSpecies objects are equal if their formulas and states match, regardless of state order.

```pycon
>>> ss5 = StatefulSpecies('CO2 v2+3v1; J=2')
>>> ss6 = StatefulSpecies('CO2 J=2; ν2+3ν1')
>>> ss5 == ss6
True
```

--------------------------------

### Represent Chemical Formulas

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/introduction.md

Instantiate and inspect chemical formulas, including ions, isotopes, and special species.

```pycon
>>> from pyvalem.formula import Formula

>>> # neutral formulas:
>>> Formula('C2H5OH')
C2H5OH

>>> # isotopes:
>>> Formula('(14C)')
(14C)

>>> # ions
>>> [Formula('H3O+'), Formula('(1H)(2H)+'), Formula('Co(H2O)6+2')]
[H3O+, (1H)(2H)+, Co(H2O)6+2]

>>> # special species
>>> [Formula('e-'), Formula('hv')]
[e-, hν]

>>> # formula attributes:
>>> Formula('Ar+2').charge
2

>>> Formula('H2(18O)').html
'H<sub>2</sub><sup>18</sup>O'

>>> print(Formula('H2(18O)').latex)
\mathrm{H}_{2}{}^{18}\mathrm{H}_{2}{}^{18}\mathrm{O}

>>> Formula('(235U)').mass
235.04392819
```

--------------------------------

### Handle AtomicConfiguration Errors

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Invalid configurations, such as repeated subshells or exceeding electron limits, raise AtomicConfigurationError.

```pycon
>>> c3 = AtomicConfiguration('[Ar].3s2')
Traceback (most recent call last):
  ...
pyvalem.states.atomic_configuration.AtomicConfigurationError: Repeated subshell in [Ar].3s2

>>> c3 = AtomicConfiguration('1s2.2s2.2p7')
Traceback (most recent call last):
  ...
pyvalem.states.atomic_configuration.AtomicConfigurationError: Too many electrons in atomic orbital: 2p7
```

--------------------------------

### Access HTML Representation

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/reaction.md

Retrieve the HTML-formatted string representation of a reaction using the html attribute.

```default
>>> print(r2.html)
CO v=1 + O<sub>2</sub> J=2 X<sup>3</sup>Σ<sup>-</sup><sub>g</sub> → CO<sub>2</sub> + O
>>> print(r4.html)
C<sub>6</sub>H<sub>5</sub>OH + 7O<sub>2</sub> → 6CO<sub>2</sub> + 3H<sub>2</sub>O
```

--------------------------------

### Access VibrationalState HTML

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Retrieve the HTML-formatted string representation of a vibrational state.

```pycon
>>> print(v5.html)
2ν<sub>1</sub> + ν<sub>2</sub> + ν<sub>3</sub>
```

--------------------------------

### Retrieve Isotopic Mass

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/formula.md

Access the exact mass for isotopically-pure molecules using the mass attribute.

```pycon
>>> f = Formula('(1H)(35Cl)+')
>>> f.mass
35.9766777262
```

--------------------------------

### Formula Class

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/formula.md

The Formula class is the primary interface for creating and interacting with chemical formula objects.

```APIDOC
## Formula(formula_string)

### Description
Instantiates a new Formula object from a chemical formula string. The string supports element symbols, isotopes in parentheses, charge notation (+n/-n), stoichiometry, and bracketed moieties.

### Attributes
- **html** (str) - Returns the formula formatted in HTML.
- **latex** (str) - Returns the formula formatted in LaTeX.
- **slug** (str) - Returns a URL-safe slug representation of the formula.
- **natoms** (int) - Returns the total count of atoms in the formula.
- **rmm** (float) - Returns the relative molecular mass.
- **mass** (float) - Returns the exact mass for isotopes and isotopically-pure molecules.
- **charge** (int) - Returns the total species charge.
- **atom_stoich** (dict) - Returns a dictionary mapping element symbols to their stoichiometric counts.

### Methods
- **stoichiometric_formula(order='atomic_number')** - Returns the stoichiometric formula as a string. The 'order' parameter can be 'atomic_number' (default) or 'alphabetical'.
```

--------------------------------

### Handle configuration errors

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Invalid configurations, such as exceeding electron capacity or repeating orbitals, raise a DiatomicMolecularConfigurationError.

```pycon
>>> c5 = DiatomicMolecularConfiguration('1σ2.2σ2.3σ3')
Traceback (most recent call last):
  ...
pyvalem.states.diatomic_molecular_configuration.DiatomicMolecularConfigurationError: Only two electrons allowed in σ orbital, but received 3

>>> c6 = DiatomicMolecularConfiguration('1σ2.2σ2.2σ1')
Traceback (most recent call last):
  ...
pyvalem.states.diatomic_molecular_configuration.DiatomicMolecularConfigurationError: Repeated orbitals in 1σ2.2σ2.2σ1
```

--------------------------------

### Access HTML Representation

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/stateful_species.md

Retrieve the HTML-formatted string of the species using the html attribute.

```pycon
>>> print(ss4.html)
CrH 1σ<sup>2</sup>.2σ<sup>1</sup>.1π<sup>4</sup>.3σ<sup>1</sup> <sup>6</sup>Σ<sup>+</sup>
```

--------------------------------

### Access quantum numbers

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Retrieve the spin (S), orbital (L), and total (J) angular momentum quantum numbers from an initialized symbol.

```pycon
>>> a0.S, a0.L, a0.J
(1.0, 1, 1.0)

>>> a1.S, a1.L, a1.J
(1.5, 2, None)

>>> a2.S, a2.L, a2.J, a2.parity
(0.5, 1, 0.5, 'o')
```

--------------------------------

### VibrationalState

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Represents molecular vibrational states for diatomic and polyatomic molecules. Initialized with a string representing the vibrational quanta.

```APIDOC
## VibrationalState

### Description
Represents molecular vibrational states. Instantiated with a string representing the vibrational excitation (e.g., 'v=n', '3v2+v3', 'v=*').

### Constructor
`VibrationalState(state_string)`

### Attributes
- **html** (string) - An HTML representation of the vibrational state.

### Example
```python
from pyvalem.states import VibrationalState
v = VibrationalState('2ν1+1ν2+ν3')
print(v.html) # 2ν<sub>1</sub> + ν<sub>2</sub> + ν<sub>3</sub>
```
```

--------------------------------

### Access Formula and States

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/stateful_species.md

Retrieve the underlying Formula object and the list of parsed State objects.

```pycon
>>> print(ss4.formula)
CrH

>>> print(ss4.states)
[1σ2.2σ1.1π4.3σ1, 6Σ+]
```

--------------------------------

### Validate Reaction Conservation

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/reaction.md

Reaction objects raise errors if charge or stoichiometry are not conserved during instantiation.

```pycon
>>> Reaction('BeH+ + I2 ⇌ BeI + HI')
Traceback (most recent call last):
  ...
pyvalem.reaction.ReactionChargeError: Charge not preserved for reaction: BeH+ + I2 ⇌ BeI + HI

>>> Reaction('BeH + I2 ⇌ BeI')
Traceback (most recent call last):
  ...
pyvalem.reaction.ReactionStoichiometryError: Stoichiometry not preserved for reaction: BeH + I2 ⇌ BeI
```

--------------------------------

### Generate HTML representation

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Access the html attribute to retrieve a formatted string for web display.

```pycon
>>> print(a2.html)
<sup>2</sup>P<sup>o</sup><sub>1/2</sub>
```

--------------------------------

### Access MolecularTermSymbol Attributes

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Shows how to retrieve quantum numbers and labels from a parsed MolecularTermSymbol object.

```pycon
>>> c6 = MolecularTermSymbol('X(4Πu_-3/2)')
>>> c6.S, c6.term_label, c6.irrep, c6.Omega
(1.5, 'X', 'Πu', -1.5)
```

--------------------------------

### Define Chemical Reactions

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/introduction.md

Represent collisional processes and reactions, with built-in validation for charge and stoichiometry.

```pycon
>>> from pyvalem.reaction import Reaction
>>> reaction = Reaction('He+2 + H -> He+ 3p1 + H+ + hv')
>>> reaction
He+2 + H → He+ 3p + H+ + hν

>>> reaction.html
'He<sup>2+</sup> + H → He<sup>+</sup> 3p + H<sup>+</sup> + hν'

>>> print(reaction.latex)
\mathrm{He}^{2+} + \mathrm{H} \rightarrow \mathrm{He}^{+} \; 3p + \mathrm{H}^{+} + h\nu
```

```pycon
>>> Reaction('(2H) + (3H) -> (4He)')
Traceback (most recent call last):
...
pyvalem.reaction.ReactionStoichiometryError: Stoichiometry not preserved for reaction: (2H) + (3H) -> (4He)

>>> Reaction('e- + Ar -> Ar+ + e-')
Traceback (most recent call last):
...
pyvalem.reaction.ReactionChargeError: Charge not preserved for reaction: e- + Ar -> Ar+ + e-
```

--------------------------------

### Validate State Uniqueness

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/stateful_species.md

StatefulSpecies raises a StatefulSpeciesError if multiple states of the same type are provided.

```pycon
>>> StatefulSpecies('N2 J=0;J=1')
Traceback (most recent call last):
  ...
pyvalem.stateful_species.StatefulSpeciesError: Multiple states of type RotationalState specified for N2 J=0;J=1

>>> StatefulSpecies('Li 1s2.2s1; 1s2.2p1')
Traceback (most recent call last):
  ...
pyvalem.stateful_species.StatefulSpeciesError: Multiple states of type AtomicConfiguration specified for Li 1s2.2p;1s2.2s
```

--------------------------------

### MolecularTermSymbol Class

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

The MolecularTermSymbol class is used to represent and parse molecular electronic term symbols. It supports various symmetry labels and quantum number configurations.

```APIDOC
## Class: MolecularTermSymbol

### Description
Represents a molecular electronic term symbol. It parses a string input containing spin multiplicity, orbital angular momentum symmetry, and optional quantum number Ω.

### Constructor
`MolecularTermSymbol(term_string)`

- **term_string** (str) - The string representation of the term symbol (e.g., '1Σ-', '3Σ+g', 'b(4Π_-3/2)').

### Attributes
- **S** (float) - Total spin angular momentum quantum number.
- **term_label** (str) - The label associated with the term symbol.
- **irrep** (str) - The electronic orbital angular momentum wave function irreducible representation.
- **Omega** (float) - The projection of the total angular momentum along the symmetry axis.
- **html** (str) - The HTML representation of the molecular term symbol.

### Example
```python
from pyvalem.states import MolecularTermSymbol

# Instantiation
term = MolecularTermSymbol('X(4Πu_-3/2)')

# Accessing attributes
print(term.S)      # 1.5
print(term.irrep)  # 'Πu'
print(term.Omega)  # -1.5
```
```

--------------------------------

### RotationalState

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

Represents the total rotational angular momentum quantum number J for atoms and molecules.

```APIDOC
## RotationalState

### Description
Represents the total rotational angular momentum quantum number, J. Instantiated with a string 'J=n' where n is an integer, half-integer, or asterisk notation.

### Constructor
`RotationalState(state_string)`

### Attributes
- **J** (float) - The parsed value of the rotational quantum number.

### Example
```python
from pyvalem.states import RotationalState
r = RotationalState('J=3/2')
print(r.J) # 1.5
```
```

--------------------------------

### Validate J with the triangle rule

Source: https://github.com/xnx/pyvalem/blob/master/docs/source/states.md

The class raises an AtomicTermSymbolError if the provided J value violates the |L-S| <= J <= L+S constraint.

```pycon
>>> a3 = AtomicTermSymbol('3P_3')
Traceback (most recent call last):
  ...
pyvalem.states.atomic_term_symbol.AtomicTermSymbolError: Invalid atomic term symbol: 3P_3 |L-S| <= J <= L+S must be satisfied.
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.