Microwave spectroscopic investigation of the Ne–acetylene van der Waals dimer

Abstract

Rotational spectra of eight isotopomers of the Ne–acetylene van der Waals dimer were measured in the frequency range of 5 to 23 GHz, using a pulsed molecular beam Fourier transform microwave spectrometer. Transitions within both the Σ₀ ground state and the Σ₁ first excited van der Waals bending state were measured for the isotopomers containing HCCH and H¹³C¹³CH, respectively. For the Ne–DCCD isotopomers, Σ₀ and Π₁ transitions were recorded, indicating a reversal of the energy level ordering upon deuterium substitution. The observed transitions indicate a Coriolis perturbation of the Σ₁ and Π₁ energy levels. The Σ₁/Π₁ state is no longer metastable for the Ne–DCCH isotopomers, so only ground state transitions were recorded. Nuclear quadrupole hyperfine structures were observed and partially resolved for isotopomers containing deuterium nuclei. The measured transition frequencies were compared to the values obtained by Bemish et al. from an ab initio potential energy surface using nuclear dynamical calculations. [R. J. Bemish, R. E. Miller, R. Moszynski, T. G. Heijmen, T. Korona, P. E. S. Wormer and A. van der Avoird, J. Chem. Phys., 1998, 109, 8968].