Detection of protonated formaldehyde in the prestellar core L1689B

Abstract

Complex organic molecules (COMs) are detected in many regions of the interstellar medium, including prestellar cores. However, their formation mechanisms in cold (~10 K) cores remain to this date poorly understood. The formyl radical HCO is an important candidate precursor for several O-bearing terrestrial COMs in cores, as an abundant building block of many of these molecules. Several chemical routes have been proposed to account for its formation, both on grain surfaces, as an incompletely hydrogenated product of H addition to frozen-out CO molecules, or in the gas phase, either the product of the reaction between H2CO and a radical, or as a product of dissociative recombination of protonated formaldehyde H2COH+. The detection and abundance determination of H2COH+, if present, could provide clues as to whether this latter scenario might apply. We searched for protonated formaldehyde H2COH+ in the prestellar core L1689B using the IRAM 30m telescope. The H2COH+ ion is unambiguously detected, for the first time in a cold (~10 K) source. The derived abundance agrees with a scenario in which the formation of H2COH+ results from the protonation of formaldehyde. We use this abundance value to constrain the branching ratio of the dissociative recombination of H2COH+ towards the HCO channel to ~10-30%. This value could however be smaller if HCO can be efficiently formed from gas-phase neutral-neutral reactions, and we stress the need for laboratory measurements of the rate constants of these reactions at 10 K. Given the experimental difficulties in measuring branching ratios experimentally, observations can bring valuable constraints on these values, and provide a useful input for chemical networks.

accepted by A&A Letters

References in corpus (8)

• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• Formation of complex organic molecules in cold objects: the role of gas phase reactions
• The origin of complex organic molecules in prestellar cores
• The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse
• Probing non polar interstellar molecules through their protonated form: Detection of protonated cyanogen (NCCNH+)
• Discovery of interstellar ketenyl (HCCO), a surprisingly abundant radical
• HCO mapping of the Horsehead : Tracing the illuminated dense molecular cloud surfaces
• The origin of gas-phase HCO and CH3O radicals in prestellar cores

Cited by in corpus (9)

• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• Discovery of HC3O+ in space: The chemistry of O-bearing species in TMC-1
• Tentative detection of HC5NH+ in TMC-1
• JCMT POL-2 and BISTRO Survey observations of magnetic fields in the L1689 molecular cloud
• A new protonated molecule discovered in TMC-1: HCCNCH+
• Vacuum ultraviolet photodesorption and photofragmentation of formaldehyde-containing ices
• Sulphur-Bearing and Complex Organic Molecules in an Infrared Cold Core
• Observations and chemical modeling of the isotopologues of formaldehyde and the cations of formyl and protonated formaldehyde in the hot molecular core G331.512-0.103
• Ortho-Para Chemistry of H2CO in the Protoplanetary Disk TW Hya