Detection of C3O in the low-mass protostar Elias 18

We have performed new laboratory experiments which gave us the possibility to obtain an estimate of the amount of carbon chain oxides (namely C(3)O(2), C(2)O, and C(3)O) formed after irradiation (with 200 keV protons) of pure CO ice, at 16 K. The analysis of laboratory data indicates that in dense molecular clouds, when high CO depletion occurs, an amount of carbon chain oxides as high as (2-3) x 10(-3) with respect to gas phase carbon monoxide can be formed after ion irradiation of icy grain mantles. Then we searched for gas phase C(2)O and C(3)O toward 10 low-mass young stellar objects. Among these we detected the C(3)O line at 38486.891 MHz toward the low-mass protostar Elias 18. On the basis of the laboratory results we suggest that in dense molecular clouds gas phase carbon chain oxides are formed in the solid phase after cosmic ion irradiation of CO-rich icy mantles and released to the gas phase after desorption of icy mantles. We expect that the Atacama Large Millimeter Array ( ALMA), thanks to its high sensitivity and resolution, will increase the number of carbon chain oxides detected in dense molecular clouds.