Abundance of HOCO+ and CO2 in the outer layers of the L1544 prestellar core

TL;DR

This study detects HOCO+ and tentative DOCO+ in the outer layers of the L1544 prestellar core, revealing insights into the chemical composition and processes in cold, dense interstellar environments.

Contribution

First detection of HOCO+ and tentative detection of DOCO+ in L1544's outer layers, with analysis of their abundance and formation pathways.

Findings

HOCO+ abundance is (5 +/- 2) x 10^-11.

Gaseous CO2 abundance is estimated at 2 x 10^-7.

HOCO+ emission originates from the external layer of the core.

Abstract

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 85.5 GHz (4,0,4-3,0,3) and 106.9 GHz (5,0,5-4,0,4), respectively, of the protonated carbon dioxide ion, HOCO+. We also report the tentative detection of the line at 100.4 GHz (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) e-11. Modelling of the chemistry involved in the formation and destruction of HOCO+ provides a gaseous CO2 abundance of 2e-7 (with respect to H2) with an upper limit of 2e-6.