Determination of the proton tunneling splitting of tropolone in the groundstate by microwave spectroscopy

Rotational spectra of tropolone in the ground vibronic state were measured by microwave spectroscopy. Due to the proton tunneling motion, the ground s tate is split into a doublet, of which the lower and upper components are d enoted by 0(+) and 0(-), respectively. In the frequency region 28-84 GHz, m ore than 150 pure rotational transitions obeying a-type selection rules wer e observed for each of the 0(+) and 0(-) states. Additionally, tunneling-ro tation transitions connecting the lower (0(+)) and upper (0(-)) components of the tunneling doublet were observed by pulsed Fourier transform microwav e spectroscopy. Twenty-three P- and Q-branch lines were observed in the fre quency region of 10-18 GHz, and analyzed combined with the pure rotational transitions for each of the 0(+) and 0(-) states. The proton tunneling spli tting in the ground state, Delta(0) = 29 193.788 +/- 0.026 MHz, and the tun neling- rotation interaction constant F = 16.456 +/- 0.015 MHz, were determ ined, as well as the rotational and centrifugal distortion constants. The d ipole 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. (C) 1999 American Institute of Physics. [S0021- 9606(99)01104-6].