Laser desorption jet-cooling spectroscopy of para-amino benzoic acid monomer, dimer, and clusters

Abstract

The technique of laser desorption followed by jet cooling allows wavelength‐selective as well as mass‐selective detection of molecules, desorbed from a surface without fragmentation. Resonance enhanced multi photon ionization (REMPI) spectra of the para‐amino benzoic acid (PABA) molecule and its methyl and n‐butyl ester were obtained in this way. The origin of the S₁←S₀ transition in PABA was found at 34173±2 cm⁻¹. The adiabatic ionization potential of PABA was determined as 7.998±0.001 eV. In addition, jet‐cooled REMPI spectra of the PABA dimer and its ring‐deuterated isotopes were recorded. The dimer is formed by two identical hydrogen bonds between the carboxylic acid groups. The excitation in the dimer is found to be almost completely localized in one monomer unit. Clusters of PABA molecules with molecules seeded in the beam (argon, methanol, water) were resonantly detected as well, using PABA as the chromophore.