Nascent hydrogen

Nascent hydrogen is claimed to non-ionised, monatomic hydrogen (formula: H), which is claimed to exist transiently but long enough to effect chemical reactions. According to one claim, nascent hydrogen is generated in situ usually by the reaction of zinc with an acid, or by electrolysis at the cathode. Being monoatomic, H atoms are much more reactive and thus much more effective reducing agent than ordinary diatomic H2, but again the key question is whether H atoms exist in any chemically meaningful way under the conditions claimed. The concept is more popular in engineering and in older literature on catalysis.

Nascent hydrogen is claimed to reduce nitrites to ammonia, or arsenic to arsine even under mild conditions. Detailed scrutiny of such claims usually points alternative pathways, not H atoms.

Notes:

Occasionally, chemisorbed hydrogen chemisorbed on metal surfaces is referred to as "nascent", although this terminology is fading with time. Other views hold that such chemisorbed hydrogen is "a bit less reactive than nascent hydrogen because of the bonds provided by the catalyst metal surface." Also, such catalyst provided atoms are not called nascent hydrogen, because they don't need to be captured and reacted in their instanteneous, temporary, "just generated" state, because the catalyst is able to reversibly generate them from the hydrogen gas supply at any time.

Nascent hydrogen refers to is "room temperature atomic hydrogen." Of course hydrogen atoms can also form at temperatures severe enough to provide the activation energy needed to rupture H2 into atoms. At room temperature high energy molecular hydrogen can also be generated with electromagnetic irradiation providing the "right energy" to dissociation:
 * H2 + hʋ(photon) &rarr; 2 H

Although not as efficiently as by reaction or electrolysis, because of quantum yield issues - basically not all photons get absorbed to create a reaction, and the majority get wasted to simply generate heat, it is claimed.

Naszierender Wasserstoff