MICROWAVE SPECTRUM, INTERNAL-ROTATION AND DIPOLE-MOMENT OF TRICHLORONITROMETHANE CL3CNO2

The microwave spectrum of gaseous trichloronitromethane, Cl3CNO2, has been investigated in detail in the frequency range from 24 to 40 GHz. The spectrum is characteristic of a low-barrier, heavy-top molecule co nsisting of a pile-up of many lines at intervals of approximately (B+C )(J+1) for the various isotopomers arising from Cl-35 and Cl-37. Some 32 lines outside of these groups have been assigned and analysed for C l3CNO2 by the internal axis method. The barrier height was determined as V-6=306.43(71) J mol(-1), almost identical with that determined ear lier for F3CNO2, and both values much larger than that obtained for H3 CNO2 (25.1173(1) J mol(-1)). A complete structure cannot be determined from the present data but the rotational constants give a C-N bond le ngth of 1.52 +/- 0.03 Angstrom, slightly longer than that in H3CNO2 bu t significantly shorter than the electron diffraction value for Cl3CNO 2. The internal rotation dynamics as evidenced by microwave spectrosco pic and electron diffraction studies of Cl3CNO2 are discussed in light of recent ab initio studies of these motions in F3CNO2. Stark effect measurements give the dipole moment of Cl3CNO2 as mu(a)=1.884(13) D. ( C) 1998 Elsevier Science B.V.