LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF ETHYL AND METHYL P-AMINOBENZOATES WEAKLY-BOUND COMPLEXES WITH POLAR-SOLVENTS (CH2F2, CH3F AND CHF3)

Weakly bound complexes derived from the combination of ethyl and methy l p-aminobenzoates (ABBE, ABME) with various polar halomethanes (CH2F2 , CHF3, CH3F) have been studied by low- and high-resolution nanosecond laser-induced fluorescence spectroscopy. The complexes were prepared in a jet pulsed supersonic expansion. Both blue- and red-shifted bands have been observed for ABME/ABEE-(CH2F2, CHF3) complexes and interpre ted as resulting from dipole-dipole and H-bonding interactions. Partia lly resolved rovibronic bands provided by high-resolution pulsed laser -induced fluorescence, in addition to spectral shifts, have been used to determine relative positions of host and solvent components and als o as the final criteria to establish the proposed geometry of the comp lexes. ABME/ABEE-(CH3F) complexes depict a different spectral pattern, showing a comparatively large red-shift structured band. This effect has been assigned to the selective deep of one of the potential energy wells produced by dipole-dipole stabilisation, effect also found in o ther H-bond weakly bound complexes. A discussion of the geometries of the complexes in relation to the anisotropy of the H-bonding and dipol e-dipole intermolecular forces is presented.