From microwave spectroscopy, bond lengths can be  determined with a correspondingly high precision, as  illustrated in this example. From the rotational microwave  spectrum of 1H35Cl, we find that B = 10.59342 cm-1.  Given that the masses of 1H and 35Cl are 1.0078250 and  34.9688527 amu, respectively, determine the bond  length of the 1H35Cl molecule.