15min:

N. R. WALKER, S. L. STEPHENS AND A. C. LEGON, School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K..

The pure rotational spectra of CF₃I NH₃ and CF₃I N(CH₃)₃ have been measured by chirped-pulse, Fourier transform microwave (CP-FTMW) spectroscopy between 7 and 18.5 GHz. Both molecules are generated by supersonic expansion of a gas sample containing a small percentage of each precursor in a balance of argon. The spectra of both complexes are consistent with C _3v prolate symmetric top structures. The observed spectrum of CF₃I NH₃ displays evidence for internal rotation of NH₃ about the principal axis. More than one hundred transitions of CF₃I NH₃ have been assigned to the internal rotor A state allowing rotational, centrifugal distortion constants and a nuclear quadrupole coupling constant for the iodine atom to be determined for this state. Measurements performed using a Balle-Flygare FTMW spectrometer further allow determination of a nuclear quadrupole coupling constant for the ¹⁴N nucleus. Many transitions in the spectrum of the CF₃I ¹⁵NH₃ isotopologue have also been measured and the length of the halogen bond between the iodine and nitrogen atoms has been determined. Measurements of hyperfine components in nine different J'' J' transitions of CF₃I N(CH₃)₃ have allowed assignment of the spectrum of this complex to determine rotational, centrifugal distortion and nuclear quadrupole coupling constants.