Structural Isomers and Tautomerism of 2-Hydroxypyridine in the Cation Ground State Studied by Zero Kinetic Energy (ZEKE) Photoelectron Spectroscopy

Abstract

The investigation of structural isomers and proton transfer phenomena of the 2-hydroxypyridine system in the cation ground state (Do) has been performed by two-color (1 +l') resonantly enhanced multiphoton ionization (REMPI) zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies of keto/enol tautomers have been determined to be 68 137 f 5 and 72 093 f 5 cm-' for 2-pyridinone and 2-hydroxypyridinol, respectively. Although the structural isomers have been reported in the neutral excited state (SI) for the keto tautomer, the observed ionization energies for these isomers were found to be the same within our experimental accuracy. This indicates that no structural isomers of the keto tautomer exist in the Do state. The keto tautomer adopts a planar geometry in the Do state similar to that in the neutral ground state. In addition, no spectroscopic evidence for fast proton transfer from the enol form to the keto form in the DO state has been obtained from the analysis of the spectral line width.

Photoionization Spectroscopy of Nucleobases and Analogues in the Gas Phase Using Synchrotron Radiation as Excitation Light Source

“…For 2-PY, ZEKE spectra provided an IE (2-PY) of 8.4479 AE 0.0006 eV and IE (2-HP) of 8.9384 AE 0.0006 eV [129], which were confirmed later by the SPES study of Poully et al [9]. Of potential interest, the corresponding spectra (Figs.…”

“…The IEs of 2-PY and of 2-HP were determined by electron impact ionization [126], photoelectron [127], resonance enhanced multiphoton ionization [128], zero kinetic energy (ZEKE) photoelectron, resonantly enhanced two-photon ionization, and mass analyzed threshold ionization (MATI) spectroscopies [129,130], and more recently by slow photoelectron spectroscopy [9]. For 2-PY, ZEKE spectra provided an IE (2-PY) of 8.4479 AE 0.0006 eV and IE (2-HP) of 8.9384 AE 0.0006 eV [129], which were confirmed later by the SPES study of Poully et al [9].…”

“…There are structural similarities between δ-valerolactam (saturated C-C bonds) and 2-pyridone (aromatic six ring cycle). δ-Valerolactam presents a small number of Reprinted with permission from Ozeki et al [129]. Copyright (1995) American Chemical Society hydrogen bonding donor-acceptor sites.…”

Electronic spectrum of 2‐pyridone+: Ab initio and time‐dependent density functional calculations

“…An ionization potential (IP) of 2‐pyridone around 9 eV is derived. Then, more accurate IPs for both the lactim and lactam forms are measured by means of zero kinetic energy (ZEKE) photoelectron, resonantly enhanced two‐photon ionization and mass‐analyzed threshold ionization (MATI) spectroscopies 23, 24. These works have revealed also the existence of a tautomerism in the cation ground state and that the cationic lactim and lactam isomers are nearly isoenergetic (Δ E ∼200 cm −1 ).…”

Decarbonylation of the 2-Hydroxypyridine Radical Cation: A Computational Study

“…[1][2][3][4][5] In the gas phase, 2-HP is slightly more stable than 2-PY, while the 2-HP radical cation (2-HP…”