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

The transient FPO molecule was produced in a flow by pyrolysis of 5% F2POPF2 in Ar at 1300-1400 degreesC. High resolution (0.008 cm(-1)) Fourier transform infrared spectra of the a-type v(1) and v(2) 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 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 and and between v(1) and v(2) + v(3). Deperturbation of the v(1) = 1 and v(2) = 1 levels was done, and the results are in support of a band center of v(3) 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 theta (e)(FPO) 110.1 degrees. 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.