TY - JOUR
T1 - Ionization energies and ionization-induced structural changes in 2-phenylethylamine and its monohydrate
AU - Yifrach, Yair
AU - Rahimi, Rami
AU - Baraban, Joshua H.
AU - Bar, Ilana
N1 - Funding Information:
We would like to acknowledge the financial support of this research by the Israel Science Foundation (ISF) founded by the Israel Academy of Sciences and Humanities.
Publisher Copyright:
© 2023 Author(s).
PY - 2023/3/21
Y1 - 2023/3/21
N2 - We report the resonance-enhanced two-photon ionization combined with various detection approaches and quantum chemical calculations of biologically relevant neurotransmitter prototypes, the most stable conformer of 2-phenylethylamine (PEA), and its monohydrate, PEA-H2O, to reveal the possible interactions between the phenyl ring and amino group in the neutral and ionic species. Extracting the ionization energies (IEs) and appearance energy was achieved by measuring the photoionization and photodissociation efficiency curves of the PEA parent and photofragment ions, together with velocity and kinetic energy-broadened spatial map images of photoelectrons. We obtained coinciding upper bounds for the IEs for PEA and PEA-H2O of 8.63 ± 0.03 and 8.62 ± 0.04 eV, within the range predicted by quantum calculations. The computed electrostatic potential maps show charge separation, corresponding to a negative charge on phenyl and a positive charge on the ethylamino side chain in the neutral PEA and its monohydrate; in the cations, the charge distributions naturally become positive. The significant changes in geometries upon ionization include switching of the amino group orientation from pyramidal to nearly planar in the monomer but not in the monohydrate, lengthening of the N-H »π hydrogen bond (HB) in both species, Cα-Cβ bond in the side chain of the PEA+ monomer, and the intermolecular O-H »N HB in PEA-H2O cations, leading to distinct exit channels.
AB - We report the resonance-enhanced two-photon ionization combined with various detection approaches and quantum chemical calculations of biologically relevant neurotransmitter prototypes, the most stable conformer of 2-phenylethylamine (PEA), and its monohydrate, PEA-H2O, to reveal the possible interactions between the phenyl ring and amino group in the neutral and ionic species. Extracting the ionization energies (IEs) and appearance energy was achieved by measuring the photoionization and photodissociation efficiency curves of the PEA parent and photofragment ions, together with velocity and kinetic energy-broadened spatial map images of photoelectrons. We obtained coinciding upper bounds for the IEs for PEA and PEA-H2O of 8.63 ± 0.03 and 8.62 ± 0.04 eV, within the range predicted by quantum calculations. The computed electrostatic potential maps show charge separation, corresponding to a negative charge on phenyl and a positive charge on the ethylamino side chain in the neutral PEA and its monohydrate; in the cations, the charge distributions naturally become positive. The significant changes in geometries upon ionization include switching of the amino group orientation from pyramidal to nearly planar in the monomer but not in the monohydrate, lengthening of the N-H »π hydrogen bond (HB) in both species, Cα-Cβ bond in the side chain of the PEA+ monomer, and the intermolecular O-H »N HB in PEA-H2O cations, leading to distinct exit channels.
UR - http://www.scopus.com/inward/record.url?scp=85150485313&partnerID=8YFLogxK
U2 - 10.1063/5.0138002
DO - 10.1063/5.0138002
M3 - Article
C2 - 36948812
AN - SCOPUS:85150485313
SN - 0021-9606
VL - 158
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 11
M1 - 114305
ER -