The fluoroformyloxyl radical geometry and ground-state rotational spectra of the free FC18O2· radical.

The rotational spectra of the isotopically substituted free fluoroformyloxyl radical FC18O2· were measured using the Prague millimeter-wave high-resolution spectrometer. More than 110 rotational-fine-hyperfine transition lines were observed and assigned to appropriate quantum numbers in the frequency range of 235–270 GHz. The obtained transition frequencies were analyzed with standard effective Hamiltonians to acquire a set of precise rotational, centrifugal-distortion, fine, and hyperfine structure molecular constants. Merging the new FC18O2· isotopologue molecular parameters with those previously obtained for the ordinary FC16O2· radical, the substitution molecular geometry in the ground vibronic state was evaluated. The molecular parameters for both radical isotopologues were also calculated by several quantum chemistry methods and their calculated mutual ratios are in remarkable agreement with the experimental FC16O2·/FC18O2· parameter ratios. The measurements, assignments of the 18-oxygen isotopologu...