Comparison of the physical properties of molecular forms of hydrogen

ordinary hydrogen hydrogen deuteride deuterium

gram molecular volume of the solid at the triple point (cu cm) 23.25 21.84 20.48

triple point (K) 13.96 16.60 18.73

vapour pressure at triple point (mmHg) 54.0 92.8 128.6

boiling point (K) 20.39 22.13 23.67

heat of fusion at triple point (cal/mole) 28.0 38.1 47.0

heat of vaporization (cal/mole) 216* 257** 293***

*At 20.39 K.

**At 22.54 K.

***At 23.67 K.