The microwave spectrum of the PF2 radical in the X̃ 2B1 ground vibronic state

Abstract

The microwave spectrum of the PF2 radical in the X̃ 2B1 ground vibronic state was observed by using a source modulation spectrometer. The radical was produced in a free-space absorption cell by a dc glow discharge in a mixture of PH3 and CF4, and 260 spectral lines were observed in the frequency region of 63–181 GHz and were assigned to 37 rotational transitions. The observed lines were least-squares analyzed to determine the rotational constants, centrifugal distortion constants, spin-rotation coupling constants with centrifugal distortion correction terms, and magnetic hyperfine coupling constants for both the phosphorus and fluorine nuclei. The εaa spin-rotation coupling constant was found to be very small: −30.041 MHz, suggesting that excited electronic states contributing to εaa are all high lying or their contributions have canceled each other. The r0 structure of PF2 was calculated from the observed rotational constants: r0(P–F)=1.5792(18) Å and θ0(FPF)=98.48 (21)° with uncertainties in parentheses. The vibrational frequencies were estimated from the observed centrifugal distortion constants to be ω1=864(14), ω2=365.3(11), and ω3=848(24) in cm−1. The Tcc dipolar hyperfine coupling constants give the spin density of the unpaired electron orbital to be 92.1% and 8.1% at P and each of F, respectively, whereas the aF Fermi coupling constants lead to the s characters of 1.64% and 0.18% at the two atoms.