The v4 = 1 and v4 = 2 rovibrational levels of PF3 revisited: New solutions for old topics

Abstract

The high-resolution infrared spectra of trifluorophosphine (PF3) were reinvestigated in the ν4 fundamental region near 350cm−1, and around 690cm−1, with the aim to provide a necessary reassignment of the 2±2 sublevel of the v4=2 overtone level. The present paper reports on the first complete study of both sublevels of v4=2 (of A1 and E symmetry, corresponding to l4=0 and ±2, respectively), through the high-resolution analysis of the overtone 2ν40 band and the 2ν4±2-ν4±1 hot band. The assignments of the latter were corrected and extended, spanning the rotational states J⩽82 and −80⩽K″·ΔK⩽48. These new infrared assignments in the v4=2 state were combined with accurate infrared, radiofrequency, centimeter-, millimeter- and submillimeter-wave data of the v4=1 level (Thiessen et al., 2000), together with rotational data in the ground vibrational state (Cotti et al., 1995), in a simultaneous fit. The existence of resonance crossings due to a Δk=±1, Δl=∓2 l-type resonance in the v4=1 state, which generated perturbation-allowed transitions, provided independent values of the C4 and Cζ4 constants. Combining these rotational transitions with the wavenumbers of the ν4 fundamental band enabled us to determine accurately the C0 axial ground state constant. Moreover, the assignment of a few, very weak rRK transitions in the 2ν4-2 overtone band and their inclusion in the global least-squares fit allowed also the first accurate experimental determination of DK0. The obtained results are (in cm−1): C0=0.159970241(29) and DK0=1.80457(49)×10−7.Quadratic, cubic, and semidiagonal quartic force fields of PF3 have been calculated at the CCSD(T) level of theory employing a variety of large correlation-consistent basis sets. These force fields have been used to evaluate spectroscopic constants which are generally found to be in very good agreement with experiment. The present best estimate of the re structure of PF3 based on an explicitly correlated coupled-cluster approach (CCSD(T)-F12b) is almost identical with its latest experimental counterpart.