National Research Council of Canada. Security and Disruptive Technologies
dimer; direct measurement; fundamental bands; hindered internal rotations; infrared spectrum; rotational constants; supersonic jets; tunneling splittings; vibrational shift; argon; ethylene; neon; quantum cascade lasers; spectroscopy; supersonic aerodynamics; van der Waals
Spectra of Ne─C₂D₄ and Ar─C₂D₄ are studied in the ν11 fundamental band region of C₂D₄ (≈2200 cm⁻¹) using a tuneable quantum cascade laser to probe a pulsed supersonic slit jet expansion. The spectra are those of perpendicular bands of near-prolate asymmetric rotors, but with a doubling of transitions due to tunneling. These tunneling splittings are due to hindered internal rotation of C₂D₄ around its C─C axis, and are more prominent for Ne─C₂D₄ than for Ar─C₂D₄. The analysis yields the first direct measurement of the A rotational constants for these complexes, and shows that the vibrational shifts are very small (<0.3 cm⁻¹). Attempts to observe the spectrum of He─C₂D₄ were not successful.
Journal of Molecular Spectroscopy289 (7 June 2013): 21–25.