The 235–360 GHz Rotational Spectrum of 1‑Oxaspiro[2.5]octa-4,7-dien-6-oneAnalysis of the Ground Vibrational State and Its 10 Lowest-Energy Vibrationally Excited States

The
millimeter-wave rotational spectrum of 1-oxaspiro[2.5]octa-4,7-dien-6-one
(1) was collected from 235 to 360 GHz. With the rotational
spectrum of this compound available for the first time, more than
5500 a- and c-type transitions were
observed and assigned for the vibrational ground state. These transitions
were least-squares fit to S- and A-reduced, sextic distorted-rotor
Hamiltonians in the Ir representation
(σfit = 37 kHz). Additionally, transitions of four
fundamental states (ν22, ν21, ν39, and ν38), four overtone states (2ν22, 3ν22, 4ν22, and 5ν22), and two combination states (ν22 + ν21 and ν22 + ν39) were measured,
assigned, and least-squares fit to single-state, S- and A-reduced,
sextic distorted-rotor Hamiltonians in the Ir representation (σfit < 42 kHz). The computed
vibration–rotation interaction constants (B0 – Bv) (MP2 and B3LYP/6-311+G(2d,p)) were compared to their corresponding
experimental values, showing excellent agreement for all fundamental
states. Based on the intensities of the transitions from six members
of the v ν22 series, the fundamental frequency of
ν22 was determined to be 79.0 (2.1) cm–1.