The reaction mechanism of atomic oxygen radical anion with vinyl radical has been investigated at the G3MP2B3 level of theory. The entrance potential energy surface for the title reaction has been scanned with a rigid scan method. Three different reaction mechanisms were observed as a direct dehydration channel, an insertion reaction and a direct bonding process, corresponding to the different initial spatial collision directions respectively. The energy-rich intermediate anions, eg. [CH2＝C—OH]－ as the initial product of the insertion reaction and [CH2＝CHO]－ as the direct bonding product, are able to isomerize and decompose to various final products, such as C2H－＋H2O, CH2C＋OH－ and CH3－＋CO. Based on the calculated relative potential barrier heights of various product pathways, the initial direct dehydration reaction was thought as the most favorable product channel for the title reaction system. Additionally, the electron transfers involved in these processes have been discussed by using the Mulliken charge population analysis. The present investigation is consistent with the previous experimental studies of the OH－＋C2H2 reaction. Moreover, the different reaction mechanisms of the O＋•C2H3, O－＋C2H4 and the present reaction were compared as well.

Key words: atomic oxygen radical anion, vinyl radical, reaction mechanism