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This work reports the identification of the gas phase amino-p-phenethylamine (APEA) conformers with computed DFT stable structures. Two-colour mass-resolved multiphoton ionisation and hole burning spectroscopies have been used to find the number of conformers and record their spectra. The spectra show the presence of four well-characterized conformers, with origin bands paired off as gauche and anti conformers, in clear contrast to the five stable structures predicted by computational methods. Several criteria have been employed to relate the experimental spectra of the conformers to stable computed structures, the ionisation energies being the most reliable for unambiguous identification. The method can be applied to other small-and medium-size biological and organic molecules.

The adiabatic ionization threshold (AIT) of trans- and gauche-benzocaine has been measured by zero electron kinetic energy-pulsed field ionization (ZEKE-PFI) spectroscopy to be 7.8412+/-0.0008 eV (lasers at 34,134.4 and 29,109.3 cm(-1)) and 7.8421+/-0.0004 eV (34,144.8+29105.7 cm(-1)), respectively. AITs computed at the B3LYP/AUG-cc-p-VDZ level for the two conformers are some approximately 2,500 cm(-1) lower than the experimental; in contrast their energy difference is very close. The trans-benzocaine cation ZEKE spectra has been recorded taking a number of S(1) intermediate vibronic states. The spectra provide an energy threshold for the appearance of intramolecular vibrational redistribution (IVR) around approximately 540 cm(-1) in the S(1) state.

The 4-aminobenzonitrile (ABN) molecule has two active sites amenable to hydrogen bonding to methanol (MeOH) and ethanol (EtOH): the amino, –NH2, and the cyano, –CN, groups. Two-color resonance enhanced multiphoton ionization time-of-flight mass spectroscopy and hole burning spectroscopy in addition to the ionization energies provides sound evidence of the occurrence of two isomers in the ABN(MeOH)1 complex and one single isomer for the ABN(EtOH)1 complex. Combining the outcomes from the ABN/methanol and ABN/ethanol experiments with ab initio computations at reliable theory levels one identifies the preferred solvation sites and the optimized geometries. A discussion of the role of the aliphatic chains on the geometry of the isomers and other properties is presented.

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