The infrared vibrationhyphen;rotation spectrum of PF5in the 1025 cmminus;1region is measured in a supersonic free jet. The spectrum in this region consists of the ngr;5(Ersquo;) and 2ngr;8(Ersquo;) bands which are strongly coupled by a Fermi interaction. The unperturbed molecular constants for both states and the interaction term are determined by including this interaction explicitly: ngr;0(ngr;5)=1025.7371(4) cmminus;1, ngr;0(2ngr;8)=1024.4483(4) cmminus;1, zgr;5=0.603thinsp;36(15), zgr;8=0.406thinsp;80(8), andW588=2.087thinsp;99(12) cmminus;1. The influence of a higherhyphen;order Coriolis interaction is identified as the origin of extraordinaryA1A2splittings in theK=1(+l) levels.
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