N-chlorodifluoromethanimine, CF2 = NCl: Quadrupole coupling and r(0) structure

The microwave spectra of (CF2)-C-12=(NCl)-N-15-Cl-35, (CF2)-C-12=(NCl)-N-15 -Cl-37, and (CF2)-C-13=(NCl)-N-14-Cl-35 have been recorded and analyzed. Ro tational, quartic centrifugal distortion and quadrupole coupling constants were determined. The off-diagonal element of the chlorine quadrupole coupli ng tensor, chi(ab), and the principal element of that tensor, chi(z), were obtained as 63.7 and -103.5 MHz, respectively, for Cl-35 (average), and 51 and -82 MHz, respectively, for Cl-37 in (CF2)-C-12=(NCl)-N-15-Cl-37. During the analysis of the spectrum of the C-13 species, it was necessary to diag onalize the complete exact Hamiltonian of the asymmetric rotor with two qua drupole nuclei because of irregular hyperfine patterns of some transitions caused by previously neglected matrix elements from the N-14 quadrupole. Ea rlier data for the normal isotopic species were re-evaluated because neglec ted off-diagonal matrix elements of the Hamiltonian led to data for chi(ab) and chi(z) inconsistent with the results obtained during this investigatio n. The rotational constants of all five isotopic species were used to deter mine the r(0) structure. All structural parameters for the planar molecule except for the difference between the CF distances could be determined. The results for the distances r(C=N) and r(NCl) and the angle alpha(CNCl) were 1.254(27) Angstrom, 1.713(17) Angstrom, and 113.62(26)degrees, respectivel y. The experimental data for the structure, the inertial defect, and the ce ntrifugal distortion constants are compared to results from ab initio calcu lations. (C) 1999 American Institute of Physics. [S0021-9606(99)01919-4].