This internship will focus on measuring mid-infrared molecular transitions of methanol (CH3OH), ammonia (NH3), and other molecules known for their enhanced sensitivity to changes in µ. The work will involve achieving subDoppler spectroscopic resolution to reach target laboratory frequency accuracies of ~100 Hz needed for comparisons with astronomical observations. This activity is part of the ANR Ultiµos project, a collaborative effort which seeks to refine current constraints on the possible variation of µ which involves leading research institutions, including Laboratoire Kastler Brossel (LKB, L. Hilico) and MONARIS (C. Janssen) at Sorbonne Université. The three partners of the Ultiµos consortium will collaborate to conduct measurements in different spectral windows, to identify transitions as targets for future Earth/space comparison campaigns, which could further tighten constraints on variations of µ. Other collaborators, such as Vrije Universiteit Amsterdam and Onsala Space Observatory, will provide theoretical and observational/astronomical support to complement the experimental efforts.