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 microwave spectrometer between 8 and 26 GHz. Three sets of rotational transitions have been assigned with the help of their Stark effects and of microwave-microwave double resonance experiments to formic acid-water, formic acid-(water)(2) and (formic acid)(2)-water. Rotational constants and some centrifugal distortion constants have been fitted for each complex, and the components of the permanent electric dipole moments have been determined from Stark splittings. Structures and binding energies from ab initio calculations have been determined to the observed formic acid-water complexes. (C) 2000 American Institute of Physics. [S0021-9606(00)01525-7].