Microwave spectra for the two conformers of propene-3-d1 and new rotational constants for these species

Propene-3-{\em d}$_1$ has two conformers: a single sy conformer with the CD bond eclipsing the C=C bondtwo equivalent asy conformers with the CD bond out of the symmetry plane of the sy conformer. In the MW spectrum the sy conformer has single transitions of a semi-rigid rotor. The asy conformer has (+) and (-) transitions as a consequence of tunneling. A MW investigation with FT accuracy and sensitivity was done in the 10-22 GHz region, where the light propene molecule has relatively few transitions strong enough to be observed. The lines were split by deuterium quadrupolar coupling. Rotational constants for the sy species are: {\em A}$_0$ = 40582.1(2), {\em B}$_0$ = 9067.04(1), and {\em C}$_0$ = 7766.02(1) MHz. We have observed the (+) and (-) transitions for the asy conformer in the same spectral region. Rotational constants fit to the averages of these lines are: {\em A}$_0$ = 43403.8(1), {\em B}$_0$ = 8659.00(2), and {\em C}$_0$ = 7718.24(2) MHz. In fitting for both conformers, the cw lines observed by Lide and Christensen for $J$ = 1 to 2$K$$_a$ = 0, 1 transitions were used to strengthen the data sets.\footnote{D. R. Lide, Jr and D. Christensen, J. Chem. Phys. 35, 1374-1378 (1961).} These new rotational constants will be used in determining a semiexperimental equilibrium structure for propene