Isomer structures and vibrational assignment of the methyl-p-aminobenzoate(H2O)(1) complex

Methyl-p-aminobenzoate(H2O)(1) complex, henceforth MAB(H2O)(1), prepared by pulsed supersonic expansion, has been examined by a broad range of laser b ased spectroscopic, mass and isomer selective techniques and density functi onal theory (DFT) calculations, in order to identify its isomer structures, ionization energies, and vibrational frequencies. The experimental techniq ues used include laser induced fluorescence (LIF), mass resolved excitation spectroscopy (MRES) either with one (REMPI) or two laser colors (R2PI), la ser excited dispersed emission (DE), high resolution MRES, pressure control led R2PI, hole burning (HB) spectroscopy, and photoion fragmentation thresh old (PIFT). Experimental results have been interpreted, rationalized and ex tended with density functional theory (DFT) computations at the B3LYP/6-31G and B3LYP/6-311G* levels. Although bare MAB molecule have four possible so lvation sites, prone to yielding hydrogen bonds with the water molecule, LI F, R2PI, and HB spectroscopy of MAB(H2O)(1) only pick out the presence of t hree blue shifted isomers, each accompanied by a number of vibrational feat ures extending to approximate to 500 cm(-1). The high intensity bands have been demonstrated to originate in three isomers and their ionization energi es, dispersed emission, vibrational spectra, and photoion fragmentation thr eshold have been measured and characterized. Isomer shifts and structures a re discussed in the light of experimental and theoretical results. (C) 2000 American Institute of Physics. [S0021-9606(00)00207-5].