Knowledge Bank

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), $NKaKc=101-000$, $202-101$, $303-202$, $211-110$, $212-111$ in the $0+$ and $0-$ states, were observed in the frequency region of $52.9-158.7$ GHz. The $0+\leftarrow 0-$ and $0-\leftarrow 0+$ proton tunneling transitions (b-type transitions), $NKaKc=111-000$, $110-101$, $211-202$, $212-201$, 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 ($\alpha$-deuteron) and the methylenic $(CH2)$ protons ($\beta$-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 $\Delta E0=1164.861(20)$ MHz. The barrier height of the double minimum potential was estimated to be $1520cm-1$ from the observed tunneling splitting assuming a one dimensional model. This potential barrier height is consistent with that of the normal species$(H2CCH),1580cm-1$, derived from the tunneling splitting reported to be $16271.8429(59)MHza$, if the zero point energy is taken into consideration.