code: public static List<IIsotope> getIsotopes(IMolecularFormula formula, IElement element) {
  
          List<IIsotope> isotopeList = new ArrayList<IIsotope>();
          for (IIsotope isotope : formula.isotopes()) {
              if (isotope.getSymbol().equals(element.getSymbol())) isotopeList.add(isotope);
  
          }
          return isotopeList;
      }
docs: Get a list of IIsotope from a given IElement which is contained
  molecular. The search is based only on the IElement.
  
  @param   formula The MolecularFormula to check
  @param   element The IElement object
  @return          The list with the IIsotopes in this molecular formula