Submillimetre-wave spectra of AsH and AsD radicals in the X³∑^- electronic state

Rotational lines of AsH and AsD radicals in their X ³∑^- ground state have been observed in the submillimetre-wave region for the first time. The AsH radical was generated by de-glow discharge in pure AsH₃ gas, and the AsD radical was generated by the reaction of arsenic powder with a mixture of D₂ and O₂ gases in a de-glow discharge. Three rotational transitions of AsH with hyperfine structure (N,J = 0,1-1,0 2,1-1,1 3,2-2,2) were measured in the frequency region 120-338 GHz, and five transitions (N,J = 0,1-1,0 2,1-1,0 2,2-1,1 4,3-3,3 5,4-4,4) of AsD in the region 173-440 GHz. The molecular constants, including the rotational constants, the spin-rotation coupling constant with the centrifugal distortion term and hyperfine coupling constants associated with the arsenic, hydrogen and deuterium nuclei, were precisely determined by least-squares fitting to the observed spectral lines. Using the results of both AsH and AsD, the Born-Oppenheimer equilibrium bond length was derived, where the adiabatic correction was taken into account: r_e^BO = 1.522 370 (86) Å.