Resonant-enhanced two photon ionization and mass-analyzed threshold ionization spectroscopy of jet-cooled 2-aminopyridines (2AP–NH2,–NHD,–NDH,–ND2)

Abstract

Resonantly-enhanced two photon ionization and mass-analyzed threshold ionization ͑MATI͒ spectra of 2-aminopyridine (2AP-NH 2) and its deuterated analogs have been obtained using two-photon ͑1ϩ1Ј͒ excitation process via S 1 intermediate states for ionization. Ionization energies of 2AP-NH 2 and 2AP-ND 2 are both precisely and accurately determined to be 8.1086Ϯ0.0005 and 8.1027Ϯ0.0005 eV, respectively. Two geometrical isomers, 2AP-NHD or 2AP-NDH, of which H or D is hydrogen-bonded to the nitrogen atom on the pyridine ring, respectively, are spectroscopically well isolated using the hole-burning spectroscopy in the S 1 states. Corresponding ionization energies are thus separately determined to be 8.1067Ϯ0.0005 or 8.1048Ϯ0.0005 eV for 2AP-NHD or 2AP-NDH, respectively. Vibrational bands of 2-aminopyridine ions associated with various aromatic ring-skeletal modes are identified in the MATI spectra and appropriately assigned with the aid of ab initio calculation. All of the ring-skeletal vibrational frequencies observed in this work become slightly higher than those in the S 1 states when the molecules are ionized, consistent with the fact that the S 1-S 0 excitation is due to *transition. According to ab initio calculation, the amino group is in the molecular plane both in the S 1 and D 0 states, while it is slightly distorted in the ground state of 2-aminopyridine. Inversion modes in 2AP-ND 2 and 2AP-NDH in S 1 states are split into two bands due to their strong coupling with the other mode, which is most probably due to torsional motion of the amino group. Strong mode couplings are clearly manifested in interferencelike patterns observed in vibrational band structures of MATI spectra taken via those two bands in S 1 states as intermediate states. A new spectroscopic scheme, in which MATI signals are used for obtaining mode-resolved spectra for the intermediate state is introduced. The vibrational band at 911 cm Ϫ1 from the S 1-S 0 origin that has been previously assigned as the inversion mode of 2AP-NH 2 is found to actually consist of two closely-spaced different modes giving two clearly-resolved different Franck-Condon active modes in corresponding MATI spectra.

DFT studies on one-electron oxidation and one-electron reduction for 2- and 4-aminopyridines

“…On the other hand, the change of the compositions of the tautomeric mixtures for neutral and charged forms of aminoazines should also be taken into account for all processes in which the charged radicals can be formed, e.g., in electrochemical or photochemical processes and during positive or negative ionization in various types of mass spectrometers when the molecule loses or gains one electron [56–58]. …”

Conical intersection seam and bound resonances embedded in continuum observed in the photodissociation of thioanisole-d3

“…The experimental details for the MATI spectroscopy have been described previously. 27,28 Briefly, the parent molecule was excited to long-lived Rydberg states using the two-color two-photon excitation scheme before being ionized by the pulsed-field ionization technique using the electric pulse of ∼160 V/cm with a delay time of ∼50 μs after the laser excitation. The MATI ions were accelerated, drifted along the time-of-flight tube, and detected by dual micro-channel plates.…”

Structure of Pyridazine in the S1 State: Experiment and Theory

“…[31,32] Briefly, pyridazine (Aldrich) heated at 80 8C was mixed with Ar carrier gas before being expanded into a vacuum through a 0.5 mm-diameter nozzle orifice. The supersonically cooled jet was skimmed through a 1 mm-diameter skimmer and then overlapped with two independently tunable laser pulses.…”