N2

N2Species(; molar_fraction, distribution, v_max=4, J_max=50,
            chi_non_resonant=4.42e-51, use_collisional_narrowing=true) -> N2Species

Constructs an N2Species and generates the transition database.

Constructor Arguments

• molar_fraction::Float64: Molar fraction of N₂ in the gas mixture.
• distribution::N2Distribution: Rovibrational population distribution, such as N2.MultiTemperatureDistribution, N2.FreeVibrationalDistribution, N2.TwoPopulationDistribution.
• v_max::Int: Maximum vibrational quantum number used to truncate the transition database.
• J_max::Int: Maximum rotational quantum number in the transition database.
• chi_non_resonant: Non-resonant susceptibility in m²V²/m³.
• use_collisional_narrowing::Bool: Whether to apply collisional narrowing.

Fields of returned type

• molar_fraction::Float64: Molar fraction of N₂ in the gas mixture.
• χ_non_resonant::Float64: Non-resonant susceptibility in m²V²/m³.
• transitions::Dict{String, Vector{N2Transition}}: Transition database.
• distribution::N2Distribution: Rovibrational population distribution.
• use_collisional_narrowing::Bool: Whether collisional narrowing is applied.

Notes

• The transition database is computed once at construction.

Examples

n2 = N2Species(
    molar_fraction = 0.9,
    distribution   = N2.MultiTemperatureDistribution(T_vib=300.0, T_rot=300.0),
)

N2.MultiTemperatureDistribution(; T_vib, T_rot, vib_states=N2.vib_states(10)) -> MultiTemperatureDistribution

Constructs a MultiTemperatureDistribution for N₂ assuming separate vibrational and rotational temperatures.

Constructor Arguments

• T_vib::AbstractFloat: Vibrational temperature in K.
• T_rot::AbstractFloat: Rotational temperature in K.
• vib_states: Vibrational states used to compute the partition sum.

Fields of returned type

• T_vib::AbstractFloat: Vibrational temperature in K.
• T_rot::AbstractFloat: Rotational temperature in K.
• Q::AbstractFloat: Total partition sum (vibrational × rotational), computed at construction. Should not be set manually.
• Q_rot::AbstractFloat: Rotational partition sum, computed at construction. Should not be set manually.

Notes

• For a system in full thermal equilibrium, set T_vib = T_rot = T_gas.

Examples

# Thermal equilibrium
dist = N2.MultiTemperatureDistribution(T_vib=1500.0, T_rot=1500.0)

# Non-equilibrium: vibrationally excited N₂
dist = N2.MultiTemperatureDistribution(T_vib=3000.0, T_rot=600.0)

N2.FreeVibrationalDistribution(; f_vib=nothing, delta_f_vib=nothing, T_rot,
                                 closure=:zero) -> FreeVibrationalDistribution

Constructs a FreeVibrationalDistribution for N₂ with freely specifiable vibrational level populations. Vibrational opulations can be specified either as absolute values f_vib or as inter-level differences delta_f_vib. Exactly one of f_vib or delta_f_vib must be provided.

Constructor Arguments

• f_vib::Vector{<:AbstractFloat}: Absolute vibrational level populations starting from v=0, normalised such that f_vib[1] = 1.0 for v = 0.
• delta_f_vib::Vector{<:AbstractFloat}: Population differences between successive vibrational levels, i.e. delta_f_vib[i] = f_vib[i+1] - f_vib[i].
• T_rot::AbstractFloat: Rotational temperature in K.
• closure::Symbol: Only used when constructing from delta_f_vib. Determines how the population of the highest vibrational level is closed.

Fields of returned type

• f_vib::Vector{AbstractFloat}: Relative vibrational level populations with f_vib[1] = 1.0 for v = 0.
• T_rot::AbstractFloat: Rotational temperature in K.
• Q::AbstractFloat: Total partition sum, computed at construction.
• Q_rot::AbstractFloat: Rotational partition sum, computed at construction.

Notes

• Exactly one of f_vib or delta_f_vib must be provided. Providing both or neither will throw an error.
• When fitting, it is more stable/robust to fit population differences. When fitting, deltafvib[1] should be fixed at 1 because the distribution gets normalized and this provides a reference to the solver. Then only deltafvib[2] and higher are fit parameters.

Examples

# From absolute populations
dist = N2.FreeVibrationalDistribution(
    f_vib = [1.0, 0.3, 0.09, 0.027], # gets normalized correctly by the function
    T_rot = 600.0
)

# From inter-level differences
dist = N2.FreeVibrationalDistribution(
    delta_f_vib = [1.0, 0.2, 0.01], # gets normalized correctly by the function
    T_rot       = 600.0,
    closure     = :zero
)

N2.TwoPopulationDistribution(; T_vib_cold, T_vib_hot, Rh, T_rot,
                                vib_states=N2.vib_states(10)) -> TwoPopulationDistribution

Constructs a TwoPopulationDistribution for N₂ representing a bimodal vibrational population consisting of a cold and a hot sub-population. (ref: J Kuhfeld et al 2021 J. Phys. D: Appl. Phys. 54 305205)

Constructor Arguments

• T_vib_cold::AbstractFloat: Vibrational temperature of the cold population in K.
• T_vib_hot::AbstractFloat: Vibrational temperature of the hot population in K.
• Rh::AbstractFloat: Fraction of molecules in the hot vibrational population ∈ [0, 1]. The cold population fraction is 1 - Rh.
• T_rot::AbstractFloat: Rotational temperature in K, shared by both populations.
• vib_states: Vibrational states used to compute the partition sums. Defaults to N2.vib_states(10), which includes the 10 lowest vibrational levels.

Fields of returned type

• T_vib_cold::AbstractFloat: Vibrational temperature of the cold population in K.
• T_vib_hot::AbstractFloat: Vibrational temperature of the hot population in K.
• Rh::AbstractFloat: Fraction of molecules in the hot vibrational population.
• T_rot::AbstractFloat: Rotational temperature in K.
• Q_cold::AbstractFloat: Partition sum of the cold population, computed at construction.
• Q_hot::AbstractFloat: Partition sum of the hot population, computed at construction.
• Q_rot::AbstractFloat: Rotational partition sum, computed at construction.

Examples

# 10% of molecules in a hot vibrational population
dist = N2.TwoPopulationDistribution(
    T_vib_cold = 500.0,
    T_vib_hot  = 5000.0,
    Rh         = 0.1,
    T_rot      = 600.0
)