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 (σ fit = 37 kHz). Additionally, transitions of four fundamental states (ν 22 , ν 21 , ν 39 , and ν 38 ), four overtone states (2ν 22 , 3ν 22 , 4ν 22 , and 5ν 22 ), and two combination states (ν 22 + ν 21 and ν 22 + ν 39 ) were measured, assigned, and least-squares fit to single-state, S- and A-reduced, sextic distorted-rotor Hamiltonians in the I r representation (σ 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 ν 22 series, the fundamental frequency of ν 22 was determined to be 79.0 (2.1) cm -1 .