Microwave spectrum, conformation, and low frequency vibrational spectrum of cyclopropylisothiocyanate

The microwave spectrum of cyclopropylisothiocyanate, c‐C3H5NCS, has been investigated in the region from 12.5 to 40.0 GHz. Two sets of a‐type R‐branch transitions were observed and assigned, on the basis of the rigid rotor model, to the trans and cis conformers. One excited vibrational state for each conformer was also identified and tentatively assigned as the asymmetric NCS torsion. The B and C rotational constants in the ground vibrational state for the trans and cis conformers of c‐C3H5NCS were found to be: B=1122.689±0.002, C=1095.619±0.002 MHz, and B=1346.859±0.003, C=1309.166±0.002 MHz, respectively. The values of the A rotational constants for both conformers were not well determined because the measured transitions are not very sensitive to these constants. The dipole moment components were determined for the trans conformer from the Stark effect to be ‖μa‖=3.11±0.02, ‖μc‖=0.62±0.01, and ‖μt‖=3.17±0.01 D and for the cis conformer to be ‖μa‖=3.34±0.01, ‖μb‖=0.27±0.07, and ‖μt‖=3.35±0.01 D. With re...