1. Hydrogen properties and technical and economic data

The atomic abundance of hydrogen in the observable universe is close to 92%. This element is clearly in the majority. It is present in ionized form in stars, in condensed form in gas giant planets, and in various forms (molecular, atomic or ionic) in interstellar gas. On Earth, it is mainly found in oxidized form, with dihydrogen occurring only marginally, for example in hydrothermal systems.

Hydrogen has three isotopes: protium ( ¹ H, more commonly referred to as H without mentioning the mass number), whose nucleus consists of a single proton, deuterium ( ² H, also referred to as D), whose nucleus contains one proton and one neutron, and tritium ( ³ H, also referred to as T), whose nucleus contains two neutrons and one proton. The...