15min:

HOLGER S. P. MÜLLER, I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany; PETR PRACNA, Academy of Sciences of the Czech Republic, 18223 Praha 8, Czech Republic; VELI-MATTI HORNEMAN, 90014 University of Oulu, Finland; STEFAN KLEE, Justus-Liebig-Universität Gießen, 35392 Gießen, Germany.

A large body of very accurate (mostly 10--20\:kHz) rotational transitions within the 10 µm tetrad of the strongly prolate symmetric rotor propyne, H₃C--CCH, had been recorded in order to analyze some weaker resonances.\footnoteP.~Pracna, G.~Graner, J.~Cosléou, J.~Demaison, G.~Wlodarczak, V.-M.~Horneman, and M. Koivusaari, J. Mol. Spectrosc. 206, (2001) 150--157; H.~S.~P.~Müller, P. Pracna, et al. , unpublished The analysis, in particular for higher K transitions, indicated new problems: Interactions of members of the 10 µm tetrad (v₅ = 1, v₉ = v₁₀ = 1, v₁₀ = 3, and v₈ = 1) with those of the 15 µm dyad (v₉ = 1 and v₁₀ = 2).

More than 300 rotational transitions within v₁₀ = 1 (E_vib = 330.9\:cm^-1) have been recorded with J'' \leq 53 and -11 \leq K l₁₀ \leq +16 for a more systematic investigation into the lower excited vibrational states of propyne. Even the inclusion of many high order terms prevented the highest K transitions to be fit within experimental uncertainties, in particular those having K l₁₀ \leq 0. Inclusion of ₁₀ IR transitions from a reanalysis of the spectrum that was used in the study of the 10 µm tetrad^a confirmed these findings. It turned out that the first order energies of the K l₁₀ = --12 levels coincide to within 1 cm^-1 with those of the overtone v₁₀ = 2, K = 12 of the l₁₀ = +2 substate. A weaker Coriolis interaction occurs between v₁₀ = 1, K l₁₀ = --11 and v₉ = 1, K l₉ = +10.\footnoteH.~S.~P.~Müller, P.~Pracna, and V.-M.~Horneman, J. Mol. Spectrosc. 216, (2002) 397--407

Meanwhile, the investigation of v₁₀ = 1 has been completed, and those of v₉ = 1 and v₁₀ = 2 have begun. Fermi-type interactions occur between the states v₁₀ = 2 and 3 and between v₉ = 1 and v₉ = v₁₀ = 1. Among the Coriolis resonances, the one between v₁₀ = 2, l₁₀ = --2 and v₅ = 1 permitted intervibrational transitions to be detected in the submillimeter region. These interactions are expected to improve A, D_K, etc. for v = 0. Selected details of our ongoing analyses will be presented. In addition, the relevance of these types of interactions for other symmetric top molecules will be discussed.