High resolution FTIR spectra of AsD3 in the 20-1000 cm-1 region. The ground, x2 = 1 and x4 = 1 states

The pure rotational spectrum of the near-spherical oblate symmetric top AsD3 has been recorded in the 20-120 cm-1 region with a resolution of 2.3 x 10-3 cm-1 employing an FT interferometer. Rotational transitions with 5 less than or equal to J less than or equal to 29 and 0 less than or equal to K less than or equal to 25 of the ground state (GS) and the x2 = 1 and x4 = 1 excited states have been assigned. Splittings were observed for the GS, K = 3 and 6 levels, the K = 3 levels of x2 and the kl = -2, 1, 4 and 7 levels of x4. Furthermore the x, y Coriolis coupled x2 and x4 bands, x0 2 = 654.4149cm-1, and x04 = 714.3399 cm-1, have been examined with a resolution of 2.4 x 10-3 cm-1, and ca. 2500 allowed and 336 ʹforbiddenʹ lines with Jʹmax = 31 and Kʹmax = 28 have been assigned. Appropriately weighted GS data comprising FIR lines, allowed and ʹforbiddenʹ (up to jK = +/-6) GS combination differences, mmw data, and jJ = 0, jK = +/-1 distortion moment transitions were fitted together, and GS parameters complete through H parameters have been determined. Two different reductions of the Hamiltonian, either with jK = +/-6 (h3) or jK = +/-3 (k) off-diagonal elements, have been employed. Equivalence of these reductions up to J = 22 was established while for J > 22 the k reduction is superior. The x2 and x4 data have been fitted with two equivalent models based on different reductions of the rovibrational Hamiltonian. In addition to the dominating x, y Coriolis resonance, ‘y24 0.520, j(k - l) = +/-3 and +/-6 interactions are important and were accounted for by the models. The transition moment ratio |M4 : M2| = 0.75 has been determined, with a positive sign of the product M2‘y24M4. An improved r0 structure, r0(AsD) = 1.51753 ? and f0(DAsD) = 92.000o, has been determined.