2016A&A...591L...2V

The L1544 prestellar core has been observed as part of the ASAI IRAM Large Program at 3 mm. These observations led to the detection of many complex molecules. In this Letter, we report the detection of two lines, at 85.5GHz (4_0,4-3_0,3) and 106.9GHz (5_0,5-4_0,4), respectively, of the protonated carbon dioxide ion, HOCO⁺. We also report the tentative detection of the line at 100.4GHz (5_0,5-4_0,4) of DOCO⁺. The non-LTE analysis of the detected lines shows that the HOCO⁺ emission originates in the external layer where non-thermal desorption of other species has previously been observed. Its abundance is (5±2)x10^–11. Modelling of the chemistry involved in the formation and destruction of HOCO⁺ provides a gaseous CO₂ abundance of 2x10^–7 (with respect to H₂) with an upper limit of 2x10^–6.