Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 1 H 1 1.00782503223(9) 0.999885(70) [1.00784,1.00811] m D 2 2.01410177812(12) 0.000115(70) T 3 3.0160492779(24) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page