A theoretical and experimental study of the ethyl-p-aminobenzoate (H2O)(n)(n=1-4) complexes

Weakly bound hydrogen bonded ethyl-p-aminobenzoate/water complexes, referre d to henceforth both as EAB/(H2O)(n) (n=1-4) or by their stoichiometry 1:n, have been investigated with a combined approach of mass and light detector laser spectroscopic techniques and ab initio calculations. The experimenta l studies follow explorations with laser induced fluorescence (LIF), and in clude one-color resonant enhanced multiphoton ionization (REMPI), two-color REMPI (R2PI), pressure dependent R2PI and hole burning (HB) spectroscopies . Calculations were conducted at the B3LYP/6-31+G(*) level and for the 1:1 complex led to the existence of six stable isomers, identified as the exper imental origin bands at +4, +6, +13, +89, +96, and +108 cm(-1) above the ba re EAB 0(0)(0) transition. It has been shown that three of these bands orig inate in the EAB trans conformer, while the other three derive from the EAB gauche conformer. None of the experimental methods used lead us to observe the EAB(H2O)(2) complex spectrum and the inspection of the EAB(H2O)(3) REM PI and R2PI spectra has been shown to be a fragmentation from the EAB(H2O)( 4) complex. The structures and identification of the set of isomers are rep orted and a comparison with the results on the family complexes methyl-p-am inobenzoate/water is discussed. (C) 2000 American Institute of Physics. [S0 021-9606(00)00643-7].