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 () was collected from 235 to 360 GHz. With the rotational spectrum of this compound available for the first time, more than 5500 - and -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 I representation (σ = 37 kHz). Additionally, transitions of four fundamental states (ν, ν, ν, and ν), four overtone states (2ν, 3ν, 4ν, and 5ν), and two combination states (ν + ν and ν + ν) were measured, assigned, and least-squares fit to single-state, S- and A-reduced, sextic distorted-rotor Hamiltonians in the I representation (σ < 42 kHz). The computed vibration-rotation interaction constants ( - ) (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 ν series, the fundamental frequency of ν was determined to be 79.0 (2.1) cm.