A lattice is defined by the unit vectors \(\rm\vec{a}_1\) = aî, \(\rm\vec{a}_2\) = −\(\rm\frac{a}{2}\)î + \(\rm\frac{a \sqrt{3}}{2}\)ĵ and \(\rm\vec{a}_3\) = ak̂, where a > 0 is a constant. The spacing between the (100) planes of the lattice is