Detection of the NCO radical in space
In the first part of this series we talked about the sulfur lost in L483. But in the studies carried out in this dark cloud, much more has been discovered. Among them, the first detection in space of the isocyanate radical (NCO) with a significant abundance.
Studying the observations of L483 carried out with the IRAM 30m radio telescope, it was seen that there were bright carbon chains such as C4H, which suggested that the region could host a propitious environment to carbon chain chemistry .
Why are carbon chains important? Most molecules observed in space can be formed only with atoms of hydrogen (H), carbon (C), nitrogen (N) and oxygen (O). These atoms are the pieces for building organic and prebiotic molecules and, together, constitute the backbone of the peptide bond that binds two amino acids and allows the construction of long proteins. Therefore, the observation of simple molecules with the C(=O)–N group in space can provide important clues about the first chemical steps in amino acid synthesis, considered key in all biological processes.
The isocyanate radical precisely consists of a C(=O)–N structure and is therefore the simplest molecule that houses the base scheme of the peptide bond. It has efficient formation mechanisms but, although it is predicted (from what the models tell us) that it must be abundant in dark clouds… its abundance is small, which complicates its detection. In addition, it has a low polarity (the higher the polarity, the more intense the lines of the molecule)  so the observed lines are weak. To this must be added the “noise” (which will depend on the observation time and the sensitivity of the instrument).
We usually use the metaphor of the field of grass that does not let you see the flowers: our field of herbs (the noise) will be reduced the higher the quality and sensitivity of our observations, letting us distinguish the “flowers”, which would be the lines of the molecules.
Technological advances are enabling us to make progress in this direction. Increasingly sensitive detectors are being built, which makes the noise less. In addition, in this work a deep survey has been carried out that has allowed us to observe in more detail, providing many unexpected results (which we will continue to talk about in the third part of this trilogy, what did you think, that we were going to tell you at once? Well, no).
How the NCO is formed
When talking about “zones” or regions in a certain environment of space, we must clarify that there is no uniformity in the conditions that give rise to the chemistry of these places. In fact, recent observations carried out with the ALMA interferometer have demonstrated a chemical differentiation in L483, which has carbon chains such as C2H that trace the envelope, and more complex organic compounds distributed around the protostar, that is, in these two areas different physical and chemical phenomena are occurring that give rise to a different chemical richness.
The detection of NCO (carried out with IRAM 30m) has taken place in the envelope of the low mass protostar in L483, and with this information it follows that the chemical processes for the formation of NCO are mainly two: one is from the reaction between CN and O2 and another would be by the recombination of the ion H2NCO+, which has also been detected in this work, thus supporting the formation of NCO by this route.
One of the important aspects of taking steps in the discoveries of new molecules is that the chemical models are updated, in this case, those related to NCO: taking into account the uncertainties in the model, the observed abundances are reproduced relatively well, which indicates that we are on the right track.
But there is still much to study. Although the survey has been of incredible sensitivity, “The next step -says Nuria Marcelino, lead author of this paper- would be to carry out NCO observations on sources that are at different stages of the star formation process. This could help us understand its role in the prebiotic chemistry of space.”
“With this survey –she continues– we have revealed the chemical richness of L483, discovering several species that had not been detected before and confirming others that had been detected tentatively. Finally, we have been able to see the flowers among the grass.”
But, friends, there are still many flowers to be revealed. We’ll look at some of them in the next part of this L483 trilogy.
 Apart from carbon chains, L483 is also rich in oxygen-carrying organic molecules such as HCO, HCCO, H2CCO, CH3CHO, HCCCHO and c-C3H2O.
 Polarity has to do with the distribution of the electric charge in the molecule. The more asymmetric the charge distribution, the more polar the molecule. The main implication of this is that, the more polar a molecule is, the more intense the lines. Therefore, as far as the NCO is concerned, the low polarity makes the lines weak, making it difficult to detect them.
This work has been published in the paper “Discovery of the elusive radical NCO and confirmation of H2NCO+ in space“, A&A 612,L10 (2018). By N. Marcelino, M. Agúndez, J. Cernicharo (Instituteof FundamentalPhysics, CSIC, Spain), E. Roueff (Sorbonne University, Paris Observatory, CNRS, France) and M. Tafalla, (National Astronomical Observatory, IGN, Spain). Based on observations carried out with the IRAM 30m radio telescope.
Image: This is what the L483 dark cloud looks like if we don’t use radio astronomy. Credit: NRAO/Gary Fuller. https://www.cv.nrao.edu/~awootten/l483/l483.html
Originally published in Spanish on the Naukas website: “Pon un radical en tu nube oscura. Trilogía de L483 (Segunda parte)” (2019/06/26).