def lambda1_Vargaftik_and_Yargin(TK):
    """Thermal conductivity of Li monomer gas

    Parameters
    ----------
    TK : float
        K, temperature

    Returns
    -------
    λ₁ : float
        W / m K, thermal conductivity

    References
    ----------
    Equation 66, page 822.
    Vargaftik, N B, and V S Yargin.
    Ch 7.4: Thermal Conductivity and Viscosity of the Gaseous Phase.
    Handbook of Thermodynamic and Transport Properties of Alkali Metals,
    edited by R. W. Ohse, 45. Blackwell Scientific Publications, 1985.

    Notes
    -----
    Valid 700 K < T < 2500 K

    Uncertainties: "for lithium vapour, ± 3 % for monatomic gas, and ± 7 % at the saturation line"
    """
    lambda1 = 1e-4 * (587.7 + 0.4562 * (TK - 1000) - 20.5e-6 * (TK - 1000)**2)
    return lambda1