  Recent laboratory experiments have demonstrated that, even though
contribution from other reaction channels cannot be neglected, unsaturated
hydrocarbons easily break their multiple C-C bonds to form CO after their
interactions with atomic oxygen. Here we present an upgraded chemical modelling
including a revision of the reactions between oxygen atoms and small
unsaturated hydrocarbons for different astrochemical environments. A first
conclusion is that towards hot cores/corinos atomic oxygen easily degrades
unsaturated hydrocarbons directly to CO or to its precursor species (such as
HCCO or HCO) and destroys the double or triple bond of alkenes and alkynes.
Therefore, environments rich in atomic oxygen at a relatively high temperature
are not expected to be rich in large unsaturated hydrocarbons or polycyclic
aromatic hydrocarbons. On the contrary, in O-poor and C-rich objects,
hydrocarbon growth can occur to a large extent. In addition, new radical
species, namely ketyl and vinoxy radicals, generated from other reaction
channels can influence the abundances of hydrocarbons towards hot cores. We,
therefore, suggest they should be included in the available databases.
Hydrocarbon column densities are calculated in the 10(13)-10(15) cm(-2) range,
in good agreement with their observed values, despite the small number of data
currently published in the literature.
