Rotational spectra of tropolone in the ground vibronic state were measured by microwave spectroscopy. Due to the proton tunneling motion, the ground state is split into a doublet, of which the lower and upper components are denoted by 0+ and 0-, respectively. In the frequency region 28-84 GHz, more than 150 pure rotational transitions obeying a-type selection rules were observed for each of the 0+ and 0- states. Additionally, tunneling-rotation transitions connecting the lower (0+) and upper (0-) components of the tunneling doublet were observed by pulsed Fourier transform microwave spectroscopy. Twenty-three P- and Q-branch lines were observed in the frequency region of 10-18 GHz, and analyzed combined with the pure rotational transitions for each of the 0+ and 0- states. The proton tunneling splitting in the ground state, Δ0 = 29 193.788 ±0.026 MHz, and the tunneling-rotation interaction constant F = 16.456±0.015 MHz, were determined, as well as the rotational and centrifugal distortion constants. The dipole moment along the a axis, responsible for the rotational transitions, was determined to be 3.428±0.050 and 3.438±0.050 D for the 0+ and 0- states, respectively.
ASJC Scopus subject areas