ROTATIONAL SPECTRUM AND RING PUCKERING OF CYCLOBUTANE-1 . $1-d_{2}$

The pure rotational spectrum of $cyclobutane-1, 1-d_{2}$ has been measured between 12-40 GHz with a pulsed microwave Fourier transform spectrometer. The assigment for transitions with $J \\leq 40$ was confirmed by microwave-microwave double resonance with a continuous pump radiation. All rotational transitions with $J > 2$ were split into a doublet due to the ring puckering motion. A coupled Hamiltonian for the two lowest states has been used to fit six rotational and five centrifugal distortion constants. The energy difference of 95.19 MHz between these two states has been determined from the rotational constants of $cyclobutane-1.l-d_{2}$ and $cyclobutane-d_{1}$ and the vibrational transition frequencies of the ring puckering of the parent and the de species.