Millimeter-wave spectroscopy, high resolution infrared spectrum, ab initio calculations, and molecular geometry of FPO

Abstract

The transient FPO molecule was produced in a flow by pyrolysis of 5% F₂POPF₂ in Ar at 1300–1400°C. High resolution (0.008 cm⁻¹) Fourier transform infrared spectra of the a-type ν₁ and ν₂ bands centered at 1297.54 and 819.57 cm⁻¹, respectively, were measured and fitted to excited state parameters up to quartic centrifugal distortion constants. Millimeter-wave spectra between 300 and 370 GHz of FPO in the ground and ₃ = 1 excited states were recorded, and 124 and 86 lines, respectively, including for both states a- and b-type transitions, were measured and fitted to a Watson A-type Hamiltonian up to sextic centrifugal distortion terms. High-level ab initio calculations with large basis sets were performed for FPO to provide reliable structural parameters as well as harmonic [CCSD(T)/AVQZ + 1] and anharmonic [MP2/VQZ + 1] force fields up to quartic terms. The spectroscopic constants derived from these force fields are generally in excellent agreement with experiment. The calculations moreover suggest anharmonic interactions between ν₂ and 2ν₃, and between ν₁ and ν₂ + ν₃. Deperturbation of the ₁ = 1 and ₂ = 1 levels was done, and the results are in support of a band center of ν₃ close to 412 cm⁻¹. Consistent experimental and theoretical equilibrium structures were determined for FPO, with r_e(PO) 145.3 pm, r_e(PF) 157.3 pm and θ_e(FPO) 110.1°. The collision-controlled 1/e life-time of FPO generated by an electric discharge in an F₂POPF₂/Ar mixture at 8–10 Pa and at room temperature is 8 ms.