Rotational spectra and structures of three hydrogen-bonded complexes between formic acid and water

Rotational transitions of several hydrogen-bonded complexes between formic acid and water have been observed with a pulsed nozzle Fourier transform mi crowave spectrometer between 8 and 26 GHz. Three sets of rotational transit ions have been assigned with the help of their Stark effects and of microwa ve-microwave double resonance experiments to formic acid-water, formic acid -(water)(2) and (formic acid)(2)-water. Rotational constants and some centr ifugal distortion constants have been fitted for each complex, and the comp onents of the permanent electric dipole moments have been determined from S tark splittings. Structures and binding energies from ab initio calculation s have been determined to the observed formic acid-water complexes. (C) 200 0 American Institute of Physics. [S0021-9606(00)01525-7].