def calThermalDiffusivity(GaThCo, GaDe, GaHeCaCoPr, GaMoWe):
    """
    calculate thermal diffusivity [m^2/s]
    args:
        GaThCo: gas thermal conductivity [J/m.s.K]
        GaDe: gas density [kg/m^3]
        GaHeCaCoPr: heat capacity at constant pressure [J/mol.K] 
        GaMoWe: gas molecular weight [kg/mol]
    """
    # try/except
    try:
        return GaThCo/(GaDe*GaHeCaCoPr/GaMoWe)
    except Exception as e:
        raise