Toward measurements of radioactive molecules for astrophysics*

With the advent of detection technology, the list of observed molecules in the Universe has been drastically elongated in the past few decades [McG21]. Although detection of molecules made of stable nuclei is suitable for locating those molecules, they do not provide the temporal information on the molecular production. On the other hand, detection of radioactive isotopes, through their characteristic gamma-rays, probe the time-scale of their production in exchange for the loss of positional resolution. This leads to the use of radioactive molecules as a sensitive tracer of stellar events as it sheds light onto both the temporal and positional information on the nucleosynthesis involved.

Typically, astronomical detections of molecules rely on radiofrequency spectroscopy of rotational transitions. Therefore, precise laboratory measurements of the rotational transitions are essential to facilitate the detection of new molecules. However, such high-precision measurements pose a challenge pertaining to radioactive isotopes because of their low production rate, short lifetime, and high velocity and internal kinetic energy. In this project, we focus on the rotational measurements of silicon monoxide, specifically ³²Si¹⁶O isotopologue (half-life: 157(7) years [ENSDF]). Since its first astronomical detection from Sagittarius B2 [Wil71], SiO has been observed extensively in our galaxy, making it a great candidate for a stellar event tracer. Based on the population of each rotational sublevel, we aim to identify the rotational energy spacing in ³²Si¹⁶O. This information will potentially guide the exploration of novel stellar events and related new physics.

[McG21] Astrophys. J., Suppl. Ser. 259 30 (2022)

[ENSDF] From ENSDF database as of July 6, 2022. Version available at http://www.nndc.bnl.gov/ensarchivals/

[Wil71] Astrophys. J. 167 L97-L100 (1971)