Experimental and theoretical study of methyl-p-aminobenzoate/ammonia complexes. I. MAB(NH3)(1)

Methyl-p-aminobenzoate(NH3)(1), complex, henceforth MAB(NH3)(1), prepared i n a pulsed supersonic expansion, has been examined by laser mass-selective spectroscopies and density functional theory calculations, aiming to ascert ain its isomer number, structures, identification, ionization energies, and vibrational assignments. Resonance enhanced multiphoton ionization and hol e burning spectra of the species in supersonic beams show two 0(0)(0) trans itions redshifted by -715 and -709 cm(-1) from that of bare MAB band origin and are plausibly associated with two different isomers, whereas ab initio calculations indicate the likely existence of five stable isomer structure s. Identification of the experimental isomer spectra with the calculated st ructures is reported and, in particular, several isomer vibrational bands a re identified by contrast with the calculated modes. Properties and feature s of the MAB(NH3)(1) are compared with those of the MAB/water complexes. (C ) 2000 American Institute of Physics. [S0021-9606(00)02240-6].