A new analysis of the ν4(E) rovibrational band of the symmetric top molecule PF3

The high-resolution Fourier transform infrared spectrum of phosphorus trifluoride PF3 have been reinvestigated in the ν4 perpendicular band region around 347 cm−1. Thanks to recent pure rotational measurements, 595 new infrared transitions of the ν4 band have been assigned extending the rotational quantum number values up to Kmax = 66 and Jmax = 67. As a consequence of this extension, a sophisticated model containing a large number of parameters and interaction constants was adopted for the analysis of the IR transitions of the ν4 fundamental band of PF3. A merge of the IR transitions and the reported MW/MM/RF data within the v4 = 1 excited level yielded an accurate rotational ground state C0 value, 0.159970436 (69) cm−1, which was used to determine an improved GS structure, r0(P-F) = 1.56324405 (11) Å and ∡(FPF) = 97.752232 (29)°. All experimental data have been refined applying various reduction forms of the effective rovibrational Hamiltonian developed for an isolated degenerate state of a symmetric top molecule. The v4 = 1 excited state of the PF3 oblate molecule was treated with models taking into account ℓ- and k-type intravibrational resonances. Parameters up to sixth order have been accurately determined and the unitary equivalence of the derived parameter sets in different reductions was demonstrated.