EPR and IR spectra of the FSO3 radical revisited: Strong vibronic interactions in the A22 electronic ground state

The ground state rotational spectrum of the fluorosulfate radical

The rotational spectra of the fluorosulfate (FSO(3)) molecular radical in its vibronic ground state were measured in the millimeter-wave region and analyzed in detail using the matrix elements of the rotational, fine, and hyperfine Hamiltonian terms. The analysis of the assigned transition frequencies made it possible to derive very precise values of the rotational, centrifugal distortion and fine structure constants and to confirm the C(3v) molecular symmetry of the vibronic ground state unambiguously. In addition, an effective parameter of the "A(1)-A(2) splitting" was determined. The rotational transitions of the FSO(3) free radical were observed, identified, and analyzed for the first time.

Rotation of methyl radicals in a solid krypton matrix

Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH(3)) in a solid krypton matrix at 17-31 K temperature range. The radicals were produced by dissociating methane by plasma bursts generated by a focused 193 nm excimer laser radiation during the krypton gas condensation on the substrate. The ESR spectrum exhibits only isotropic features at the temperature range examined, and the intensity ratio between the symmetric (A) and antisymmetric (E) spin state lines exhibits weaker temperature dependence than in a solid argon matrix. However, the general appearance of the methyl radical spectrum depends strongly on temperature due to the pronounced temperature dependency of the E state linewidths. The rotational energy level populations are analyzed based on the static crystal field model, pseudorotating cage model, and quantum chemical calculations for an axially symmetric, planar rotor. Crystal field strength parameter values of -140 cm(-1) in Ar and -240 cm(-1) in Kr match most closely the experimentally observed rotational energy level shifts from the gas phase value. In the alternative model, considering the lattice atom movement in a pseudorotating cage, the effective lowering of the rotational constants B and C to 80%-90% leads to similar effects.