15min:

EUNSOOK KIM AND SATOSHI YAMAMOTO, Department of Physics and Research Center for the Early Universe, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.

The 1₀₁ - 0₀₀ rotational transition of the C₂D₃ radical in the ground electronic state has been detected for the first time with the Fourier transform millimeter-wave (FTMW) spectrometer. The C₂D₃ radical is produced by discharging the C₂D₃Br gas diluted in Ar. Thirty-two fine and hyperfine components of the 1₀₁ - 0₀₀ transition are observed in the frequency region around 44.4 GHz. We determined the rotational constant, the spin-rotation interaction constant, and the hyperfine interaction constants accurately for the s and a states caused by the tunneling motion in the CCD rocking mode. From the nuclear quadrupole interaction constant _aa of the deuteron determined in the present study, the angle between the C-D bond and the a-axis is estimated to be 148.5^\circ. Furthermore, the lower limit of the energy difference between the s and a states is estimated to be 0.01 cm^-1 on the basis of the hyperfine interaction, indicating that the tunneling motion is significant even for C₂D₃.