The rotational spectrum of trifluoromethyl isocyanate

Authors:

• Jacek Koput,
• W. Stahl,
• N. Heineking,
• G. Pawelke,
• B. Steger,
• D. Christen

Abstract

The rotational spectrum of trifluoromethyl isocyanate, CF₃NCO, in the ground vibrational state has been measured in the region 3-15 GHz using a molecular beam Fourier transform spectrometer. The spectrum was analyzed using two theoretical models: the model of a semirigid molecule with internal rotation of the trifluoromethyl group and the quasi-symmetric-top model. The nuclear hyperfine structure of 32 a-type J + 1 ← J rotational transitions, with J = 0 to 3, arising from molecules in two sublevels of the ground torsional state was analyzed, yielding values of all the nonvanishing quadrupole coupling constants. The spectroscopic parameters of trifluoromethyl isocyanate were determined, and the molecule was found to be a nearly prolate symmetric rotor with the rotational constants A = 5675 MHz, B = 1752.524 MHz, and C = 1746.132 MHz. The barrier to internal rotation of the trifluoromethyl group was found to be 48 cm^-1. Some of the structural parameters were determined from the rotational constants. In addition, the values of the molecular parameters were estimated in ab initio calculations. © 1994 Academic Press, Inc.