Submillimetre-wave spectrum, 14N-hyperfine structure, and dipole moment of cyclopropyl cyanide

The room-temperature rotational spectrum of cyclopropyl cyanide (c-C3H5CN) has been investigated in selected frequency regions from 85 to 680 GHz using a source-modulation submillimetre-wave spectrometer. More than 450 transitions have been measured spanning the quantum numbers 12⩽J⩽103 and 0⩽Ka⩽48 for the most abundant isotopic species. All lines have been fit together with previously published data to yield refined rotational and centrifugal distortion constants that permit accurate frequency predictions. The rotational spectra of the 13C- and 15N-containing isotopologues, observed in natural abundance, have also been investigated at 85-410 GHz. Complementary measurements were performed also at 6.7-14.2 GHz on low-J lines of the normal isotopologue, which were observed in supersonic expansion and with fully resolved 14N-nuclear quadrupole hyperfine structure. The electric dipole moment components of cyclopropyl cyanide were also redetermined from Doppler-free Stark effect measurements and are μa=4.1221(31)D,μc=0.9026(9)D, and μtot=4.2197(30)D.