PSEUDOROTATION PATHWAY AND EQUILIBRIUM STRUCTURE FROM THE ROTATIONAL SPECTRUM OF JET-COOLED TETRAHYDROFURAN

The rotational spectrum of jet-cooled tetrahydrofuran has been investigated in the 8–18 and 60–78 GHz frequency ranges. Only the four lowest vibrational levels remain populated in the jet conditions. Two pseudorotation vibrational spacings have been measured directly to be ΔE01=21 307.71(3) MHz and ΔE23=61 205.69(3) MHz. They have been used, together with the lowest 10 measured far infrared transition frequencies and with the effective moments of inertia of the ground state and their shifts upon excitation observed in this work, to determine the potential energy function for pseudorotation and the associated structural relaxations. The potential energy barriers are 45 cm−1 at the envelope conformation of the oxygen and 16 cm−1 at the twisted conformation of the Cβ–Cβ′ bond relative to the CαOCα′ plane. The four symmetrically equivalent equilibrium structures are close to the envelope conformations of the CH2 groups next to the oxygen atom. While the C–O bond lengths and the local CH2 angles appeared to re...