High-resolution molecular spectroscopy of open shell molecules: isotopologues of the imidogen (15ND) and amidogen (15ND2) radicals

High-resolution molecular spectroscopy of open shell molecules: isotopologues of the imidogen (15ND) and amidogen (15ND2) radicals Dore Luca 1, Bizzocchi Luca 2, Degli Esposti Claudio 1, Melosso Mattia 1, Tamassia Filippo 3 1 Dipartimento di Chimica “Giacomo Ciamician”, Università di Bologna, Via Francesco Selmi 2, I-40126 Bologna, Italy 2 Centre for Astrochemical Studies, Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße 1, D-85749 Garching bei München, Germany 3 Dipartimento di Chimica Industriale “Toso Montanari”, Università di Bologna, Via del Risorgimento 2, I-40136 Bologna, Italy A wide number of studies have been carried out on the imidogen and amidogen radicals, which are thought to be involved in the ion-reaction scheme in which ammonia is produced from N+. The rotational spectrum of the main isotopologue of the imidogen radical NH has been investigated in the THz region as well as in the Far-Infrared-Region [1]. In addition, the less common isotopologues ND and 15NH have been studied by rotational spectroscopy [2,3,4]. The interest on this small free radical has increased, since both NH and ND have been detected is several astronomical sources [5,6]. However, no data on the rare isotopologue 15ND were available until now. In this work, 15ND radical has been produced by DC-glow discharge of 15ND3 and Ar and its pure rotational spectrum has been recorded up to 1.2 THz. The fine and hyperfine structure of the N = 1 ← 0 and N = 2 ← 1 transitions has been assigned and all the measured line frequencies have been analyzed, allowing to determine the rotational constant B, the centrifugal distortion term D and 9 fine and hyperfine parameters. A global analysis including ro-vibrational data of all the isotopologues of NH radical is in progress. While discharging ammonia, the spectrum of another radical, rapidly identified as 15ND2, appeared (Fig. 1). In fact, imidogen and amidogen radicals are usually obtained in the same conditions. Although the amidogen radical has been subjected to numerous studies [7,8,9], no spectroscopic data on 15ND2 are reported. In the second part of our work, the rotational spectrum of the 15ND2 radical has been observed in selected frequency regions between 264 GHz and 1.2 THz. A total of 164 transitions have been recorded and assigned, whose analysis allowed us to determine with high accuracy the rotational constants, some centrifugal distortion terms and 21 fine and hyperfine parameters. References: [1] Flores-Mijangos J. et al., J. Mol. Spectrosc., 225, 189-195 (2004). [2] Saito S. et al., ApJ., 410, L53-L55, 1993. [3] Dore L. et al., Mol. Phys., 109, 2191-2198 (2011). [4] Bailleux S. et al., A&A, 538, A135 (2012). [5] Meyer M.D. et al., ApJ., 376, L49-L52 (1991). [6] Bacmann A. et al., A&A, 521, L42 (2010). [7] Muller H.S.P. et al., J. Mol. Spectro., 195, 177-184 (1999). [8] Kanada M. et al., AIP, 94, 3423 (1991). [9] Margulès L. et al., A&A, 591, A110 (2016).