The Millimeter- and Submillimeter-Wave Spectrum and the Dipole Moment of Ethylenimine.

The rotational spectrum of ethylenimine (aziridine, c-C(2)H(4)NH) has been investigated in selected regions from 118 to 950 GHz using the Cologne terahertz spectrometer. About 320 lines have been measured spanning the quantum numbers 2 </= J </= 59 and 0 </= K(c) </= 50. All lines have been fit together with previously published data to yield refined ground state constants such as A = 22 736.19294(31) MHz, B = 21 192.46114(31) MHz, and C = 13 383.16401(30) MHz and centrifugal distortion constants that permit accurate frequency predictions. FTMW measurements were performed at the ETH Zürich to redetermine the dipole moment, to improve (14)N-quadrupole-coupling constants, as well as to determine (14)N-spin-rotation coupling constants. The most reliable values for the components of the dipole moment are µ(b) = 0.97(12) D and µ(c) = 1.357(25) D determined by the Stark- and additional intensity measurements of appropriate b- and c-type transitions. Moreover, we performed quantum chemical calculations of the dipole moment of ethylenimine that confirm these experimental results. This three-membered ring molecule is of potential astrophysical interest. Copyright 2000 Academic Press.