15min:

MASATO HAYASHI, KENSUKE HARADA, KEIICHI TANAKA AND TAKEHIKO TANAKA, Department of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki, Higashiku, Fukuoka 812-8581, Japan; RICHARD LAVRICH, National Institute of Standards and Technology, USA.

~~The rotational and proton tunneling spectra of the vinyl-d (H₂CCD) radical have been observed by millimeter wave spectroscopy combined with a pulsed supersonic jet technique. H₂CCD was generated by the 193 nm excimer laser photolysis of vinyl chloride-d(H₂CCDCl). The pure rotational transitions ( a -type transitions), N_K_aK_c =1₀₁-0₀₀, 2₀₂-1₀₁ , 3₀₃-2₀₂, 2₁₁-1₁₀, 2₁₂-1₁₁ in the 0⁺ and 0^- states, were observed in the frequency region of 52.9-158.7 GHz. The 0⁺ 0^- and 0^- 0⁺ proton tunneling transitions ( b -type transitions), N_K_aK_c =1₁₁-0₀₀, 1₁₀-1₀₁ , 2₁₁-2₀₂, 2₁₂-2₀₁, were observed in the frequency region of 184.7-236.8 GHz. The observed rotational lines were split into fine and hyperfine components due to the spin-rotation interaction and the spin- nuclear spin interaction of the acetylenic (CD) deuteron ( -deuteron) and the methylenic (CH₂) protons ( - protons). The moleculer constants such as rotational constants, spin- rotation interaction constants, and hyperfine interection constants, were determined by a least squares fitting of the observed spectrum, together with the proton tunneling splitting E₀ = 1164.861(20) MHz. The barrier height of the double minimum potential was estimated to be 1520 cm^-1 from the observed tunneling splitting assuming a one dimensional model. This potential barrier height is consistent with that of the normal species(H₂CCH), 1580 cm^-1, derived from the tunneling splitting reported to be 16271.8429(59) MHz , if the zero point energy is taken into consideration.