def f_factor(p, t):
    """Enhancement factor for calculating mole fraction.

    Parameters
    ----------
    p : float
        Pressure in Pascal.
    t : float
        Temperature in degree Celsius.

    Returns
    -------
    f : float
        Enhancement factor needed in calculation of mole fraction.

    Notes
    -----
    See section A-II of
    http://emtoolbox.nist.gov/Wavelength/Documentation.asp.

    """
    alpha = 1.00062
    beta = 3.14e-08
    gamma = 5.6e-07
    return alpha + beta * p + gamma * t ** 2
