The Cl₂ molecules in crystalline chlorine are arranged in herringbone arrays within sheets, held together by covalent bonds. The shortest Cl to Cl distance within these sheets is 1.98 $\stackrel{\mathrm{o}}{\mathrm{A}}$. Adjacent sheets are held together by van der Waals' forces and the closest approach between Cl atoms on neighboring sheets is 3 .69 $\stackrel{\mathrm{o}}{\mathrm{A}}$. In solid HCI observed at lower temperatures, the H-Cl bond length is 1.25 $\stackrel{\mathrm{o}}{\mathrm{A}}$. Therefore shortest distance between two Cl atoms in solid HCI is (given van der Waals' radius of H =1.1$\stackrel{\mathrm{o}}{\mathrm{A}}$):