  Acetylene, among the multitude of organic molecules discovered in space,
plays a distinct role in the genesis of organic matter. Characterized by its
unique balance of stability and reactivity, acetylene is the simplest
unsaturated organic molecule known to have a triple bond. In addition to its
inherent chemical properties, acetylene is one of the most prevalent organic
molecules found across the Universe, spanning from the icy surfaces of planets
and satellites and the cold interstellar medium with low temperatures to hot
circumstellar envelopes where temperatures surge to several thousand kelvins.
These factors collectively position acetylene as a crucial building block in
the molecular diversification of organic molecules and solids present in space.
This review comprehensively discusses the formation and expansion of carbon
skeletons involving acetylene, ranging from the formation of simple molecules
to the origination of the first aromatic ring and ultimately to the formation
of nanosized carbon particles. Mechanisms pertinent to both hot environments,
such as circumstellar envelopes, and cold environments, including molecular
clouds and planetary atmospheres, are explored. In addition, this review
contemplates the role of acetylene in the synthesis of prebiotic molecules. A
distinct focus is accorded to the recent advancements and future prospects of
research into catalytic processes involving acetylene molecules, which is a
significant instrument in driving the evolution of carbon complexity in the
Universe. The insights garnered from this review underline the significance of
acetylene in astrochemistry and potentially contribute to our understanding of
the chemical evolution of the Universe.
