The HO radical is linked with the production of HO in molecular clouds. Studies of HO distribution in Taurus Molecular Cloud-1 (TMC-1) suggest that in dense gas, HO is mainly formed by dissociative recombination of HO. Dissociative recombination is the reaction in which a molecular ion recombines with an electron and dissociates into neutral fragments. Important formation mechanisms for HO are:
HO + e → HO + H (1a)  Dissociative recombination
HO + e → HO + H + H  (1b)  Dissociative recombination
HCO + e → HO + CO     (2a)     Dissociative recombination
O + HCO → HO + CO                        (3a)   Neutral-neutral
H + HO → HO + H + H     (4a) Ion-molecular ion neutralization