High resolution FTIR spectra of AsD3 in the 20-1000 cm−1 region. The ground, 98, v2 = 1 and v4 = 1 states

Abstract

The pure rotational spectrum of the near-spherical oblate symmetric top AsD3 has been recorded in the 20–120cm−′ region with a resolution of 2.3 × 10−3 m−1 employing an FT interferometer. Rotational transitions with 5 ⩽ J ⩽ 29 and 0 ⩽ X ⩽ 25 of the ground state (GS) and the v2 = 1 and v4 = 1 excited states have been assigned. Splittings were observed for the GS, 98, K = 3 and 6 levels, the K = 3 levels of v2 and the kl = −2, 1, 4 and 7 levels of v4. Furthermore the x,y Coriolis coupled v2 and v4 bands, v 0 2 = 654.4149cm−1, and v 0 4 = 714.3399 cm−1, have been examined with a resolution of 2.4 × 10−3 cm−1, and ca. 2500 allowed and 336 ‘forbidden’ lines with J′max = 31 and K′max = 28 have been assigned. Appropriately weighted GS data comprising FIR lines, allowed and ‘forbidden’ (up to ΔK = ±6) GS combination differences, mmw data, and ΔJ = 0, ΔK = ±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 ΔK = ±6 (h3) or ΔK = ±3 (ε) off-diagonal elements, have been employed. Equivalence of these reductions up to J = 22 was established while for J > 22 the ε reduction is superior. The v2 and v4 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, ζ y 24 0.520, Δ(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 M 2ζ y 24 M 4. An improved r0 structure, r0(AsD) = 1.51753 Å and α0(DAsD) = 92.000°, has been determined.