code: def get_nmr_quadrupole_moment(self, isotope=None):
          
  
          quad_mom = self._el.nmr_quadrupole_moment
  
          if len(quad_mom) == 0:
              return 0.0
  
          if isotope is None:
              isotopes = list(quad_mom.keys())
              isotopes.sort(key=lambda x: int(x.split("-")[1]), reverse=False)
              return quad_mom.get(isotopes[0], 0.0)
          else:
              if isotope not in quad_mom:
                  raise ValueError("No quadrupole moment for isotope {}".format(
                      isotope))
              return quad_mom.get(isotope, 0.0)
docs: Gets the nuclear electric quadrupole moment in units of
          e*millibarns
  
          Args:
              isotope (str): the isotope to get the quadrupole moment for
                  default is None, which gets the lowest mass isotope