The millimeter- and submillimeter-wave spectrum and the dipole moment of ethylenimine

The rotational spectrum of ethylenimine (aziridine, c-C2H4NH) has been inve stigated in selected regions from 118 to 950 GHz using the Cologne terahert z spectrometer. About 320 lines have been measured spanning the quantum num bers 2 less than or equal to J less than or equal to 59 and 0 less than or equal to K-c less than or equal to 50. All lines have been fit together wit h 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(3 0) MHz and centrifugal distortion constants that permit accurate frequency predictions. FTMW measurements were performed at the ETH Zurich to redeterm ine the dipole moment, to improve N-14-quadrupole-coupling constants, as we ll as to determine N-14-spin-rotation coupling constants. The mast reliable values for the components of the dipole moment are mu(b) = 0.97(12) D and mu(c) = 1.357(25) D determined by the Stark- and additional intensity measu rements of appropriate b- and c-type transitions. Moreover, we performed qu antum chemical calculations of the dipole moment of ethylenimine that confi rm these experimental results. This three-membered ring molecule is of pote ntial astrophysical interest. (C) 2000 Academic Press.