The rotational spectrum of Methylarsine

R.A. Motiyenko (1, 2) , V.V. Ilyushin (3) , J. Demaison (1) , N. Vogt (4) , L. Margulès (1, 2) , H. Møllendal (5) , Jean-Claude Guillemin (6)

1 PhLAM - Laboratoire de Physique des Lasers, Atomes et Molécules - UMR 8523
2 PMI - Physique Moléculaire aux Interfaces
3 KhNU - V.N. Karazin Kharkiv National University
4 MSU - Lomonosov Moscow State University
5 UiO - University of Oslo
6 ISCR - Institut des Sciences Chimiques de Rennes

The rotational spectrum of an organoarsenic compound, methylarsine, CH3AsH2, was studied in the frequency range 10–80 GHz using the Stark-modulated spectrometer in Oslo, and in the frequency range 150–660 GHz using the Lille spectrometer. The experimental work was augmented by high-level ab initio calculations. The analysis of large amplitude torsional motion in CH3AsH2 was performed using the rho axis method and the RAM36 code modified to take into account the nuclear quadrupole hyperfine structure. The final fit used 48 parameters (including 3 parameters of quadrupole coupling) to give an overall unitless root-mean-square deviation of 0.92 for the dataset consisting of 2753, 991, and 414 transitions belonging, respectively, to the ground, first, and second excited torsional states. Compact grouping of rotational transitions due to the small asymmetry (κ=-0.9986), torsional splittings due to internal rotation of the CH3 group, and relatively large hyperfine splittings due to a rather large value of the arsenic nuclear quadrupole moment (χaa=35.4 MHz, χcc=−117.2 MHz, χac=115.7 MHz) represent an interesting case of interplay of different splittings in a molecule with a rather strong coupling between internal and overall rotations (ρ=0.413).

Mots clés: Methylarsine; Microwave spectrum; Quadrupole hyperfine structure; Torsional large amplitude motion

Domaines: Chimie

R.A. Motiyenko, V.V. Ilyushin, J. Demaison, N. Vogt, L. Margulès, et al.. The rotational spectrum of Methylarsine. Journal of Molecular Structure, 2020, 1213, pp.128037. ⟨10.1016/j.molstruc.2020.128037⟩. ⟨hal-02569942⟩