Infrared diode laser spectroscopy of the PF radical

The infrared absorption spectrum of the PF radical in the X 3Σ− ground electronic state has been observed using a Zeeman modulated diode laser spectrometer. The radical was produced in a multiple‐reflection absorption cell by a dc glow discharge in a mixture of PH3 and CF4. The F1 and F3 spin components of five vibration–rotation transitions of the v=1–0 band have been recorded in the region of 823 to 830 cm−1. By constraining molecular constants of the v=0 state to the values previously determined by microwave spectroscopy, the band origin, the vibration–rotation constant αB=B0−B1, and the vibrational change of the spin–spin interaction constant αλ=λ1−λ0 have been determined from the observed spectrum to be 837.816 36(70), 0.004 639 4(70), and −0.005 04(91) in cm−1, respectively, with one standard deviation in parentheses. The sign of αλ is the same as those of NCl and PCl, but is opposite to those of O2, SO, S2, and SeO.