Laser mass-resolved spectroscopy and theoretical study of $methyl-p-aminobenzoate(H2O)n$ $(n=2,3,4)$ complexes Available to Purchase

A combined computational and experimental study of the $methyl-p-aminobenzoate(H2O)n,$ $(n=2,3,4)$ complexes $[MAB(H2O)n]$ is reported. Complexes potential energy surfaces were explored by ab initio density functional theory (DFT) methods, at the B3LYP/6-31G level, and the stable isomer structures and vibrational modes further computed at the $B3LYP/6-31+G*$ level. A set of self-contained experimental techniques, including laser induced fluorescence (LIF), resonance enhanced multiphoton ionization mass-resolved spectroscopy (REMPI), two-color resonance enhanced multiphoton ionization mass-resolved spectroscopy (R2PI), “hole burning” spectroscopy (HB), and two-color ionization thresholds were used to study the spectra and other physical features of the complexes. Of the three title complexes only $MAB(H2O)4$ has been observed with our experimental methods, while the $MAB(H2O)3$ was formed by evaporation and $MAB(H2O)2$ was not detected at all. It has been shown that the observed $MAB(H2O)4$ complex has only one isomer with a hydrogen bonded water ring structure attached to the amino hydrogens and its low vibrational modes (up to 165 cm⁻¹) have been assigned. A discussion of the results, including structures of stable isomers, isomer energies, ionization thresholds, and the difficulties in observing some solvated complexes is presented.