code: public static IAtomContainer getAtomContainer(String formulaString, IChemObjectBuilder builder) {
          return MolecularFormulaManipulator.getAtomContainer(MolecularFormulaManipulator.getMolecularFormula(
                  formulaString, builder));
      }
docs: Converts a formula string (like "C2H4") into an atom container with atoms
  but no bonds.
  
  @param formulaString the formula to convert
  @param builder a chem object builder
  @return atoms wrapped in an atom container