Laboratory Investigation of reactive species by Spectral Taxonomy – LISTed

We have exploited and completed the intrumentation for experimental molecular spectroscopy in the millimeter and submillimeter wave domain in our laboratory. We utilized two spectrometers: one based on a frequency multiplication chain (75-900 GHz range) and the other employing the chirped-pulse technique (75-110 GHz) to study various molecular species. We have developed different cells, allowing the study of both stable species (long absorption path cell) and radicals (reaction cells with atomic fluorine for hydrogen abstraction).

We also implemented the spectral taxonomy method, which enables the rapid identification of new molecular species in a complex mixture, in the millimeter range.

We studied several molecular species in the laboratory as part of the LISTed project. These studies can be categorized into two main groups:

- Study of carbon-based molecules with low reactivity (stable under laboratory conditions).

- Study of radicals obtained through dehydrogenation of an organic precursor.

In the first category, we examined molecules containing one or more -CN groups derived from adamantane, benzene, norbornadiene, and ethynylbenzene, resulting in four publications in peer-reviewed journals.

In the second category, we focused on radicals produced from the dehydrogenation of methanol, acetonitrile, acetaldehyde, and formamide, which led to five publications.

In the latter example, the observation of the H2NCO radical from the dehydrogenation of formamide marked the first laboratory detection of this species. We implemented the spectral taxonomy procedure to quickly identify the radical. Searches for H2NCO in the interstellar medium have undertaken but remain unsuccessful to date.

The data we obtained as part of the LISTed project are now available into databases on molecules of astrophysical interest and are accessible to astrophysicists for analyzing each of their new observations. We will continue our efforts to study new candidate species for interstellar detection, particularly short-lived species under laboratory conditions.

Studying star- and planet-forming regions in our galaxy provides important clues about the chemical history of the Solar System and the origin of life on Earth. To interpret such clues, it is crucial to identify which molecules are present which implies that they have previously been investigated in the laboratory. The principal investigator of this project has recently contributed to the development of a new experimental technique, the microwave spectral taxonomy, enabling the identification of new molecules in exotic chemical mixtures in the centimeter-wave domain. In this project, spectral taxonomy will be extended to the millimeter-wave domain, a spectral region with a renewed interest due to the advent of powerful radiointerfereometers, both extremely sensitive and resolutive, such as NOEMA and ALMA. The obtained molecular fingerprints will enable astronomers to look for new reactive species in the interstellar medium using these instruments and thus to understand better the chemical and physical processes in space.