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 I-r representation (sigma(fit) = 37 kHz). Additionally, transitions of four fundamental states (nu(22), nu(21), nu(39), and nu(38)), four overtone states (2 nu(22), 3 nu(22), 4 nu(22), and 5 nu(22)), and two combination states (nu(22) + nu(21) and nu(22) + nu(39)) were measured, assigned, and least-squares fit to single-state, S- and A-reduced, sextic distorted-rotor Hamiltonians in the I-r representation (sigma(fit) < 42 kHz). The computed vibration-rotation interaction constants (B-0 - B-v) (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 nu(22) series, the fundamental frequency of nu(22) was determined to be 79.0 (2.1) cm(-1).