アイテム詳細

要旨

The high-resolution infrared spectra of trifluorophosphine (PF₃) were reinvestigated in the ν₄ fundamental region near 350 cm⁻¹, and around 690 cm⁻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 2V₄⁰ band and the V₄^±2 – V₄^±1hot 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 ^rR_K transitions 2ν₄⁻² overtone band and their inclusion in the global least-squares fit allowed also the first accurate experimental determination of D_K⁰. The obtained results are (in cm⁻¹): C₀ = 0.159970241(29) and D_K⁰=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.