Isomer‐Selective Generation and Spectroscopic Characterization of Picolyl Radicals

Abstract

Nitrogen-containing resonance-stabilized radicals such as the picolyl radical are important in combustion chemistry and astrochemistry. They have only been scarcely studied because an isomer-selective generation is often difficult. Herein, we present threshold photoelectron spectra of the three picolyl radical isomers, C H N, that were obtained with synchrotron radiation. The radicals were selectively generated by flash pyrolysis from aminomethylpyridine precursors through deamination. Ionization energies of 7.70, 7.59, and 8.01 eV were determined for 2-, 3-, and 4-picolyl, respectively. The observed vibrational structure was assigned to an in-plane deformation mode of the aromatic ring. The spectroscopic insight gained in this study can be used to distinguish different picolyl isomers in on-line combustion analysis, for example.

Decomposition of Picolyl Radicals at High Temperature: A Mass Selective Threshold Photoelectron Spectroscopy Study

“…Recently we investigated the photoionization of the three picolyl isomers, designated 4, 5 and 6 in Scheme1,employing mass selective threshold photoelectrons pectroscopy( ms-TPES) and obtained ionization energies (IE) of 7.70 AE 0.02, 7.59 AE 0.01 and 8.01 AE 0.01 eV for 4, 5 and 6. [1] In addition, av ibrational progression assigned to an in-plane deformation mode of the aromatic ring was observed for all three of them. [1] Here we extendo ur work further and investigate the hightemperature chemistry of the picolyl radicals, as generated by pyrolysis of the aminomethylpyridines 1, 2 and 3 (see Scheme1.Identified products and possible pyrolysis pathway of the three aminomethylpyridines 1, 2 and 3.…”

“…[1] In addition, av ibrational progression assigned to an in-plane deformation mode of the aromatic ring was observed for all three of them. [1] Here we extendo ur work further and investigate the hightemperature chemistry of the picolyl radicals, as generated by pyrolysis of the aminomethylpyridines 1, 2 and 3 (see Scheme1.Identified products and possible pyrolysis pathway of the three aminomethylpyridines 1, 2 and 3. Scheme 1).…”

“…Recently we investigated the photoionization of the three picolyl isomers, designated 4 , 5 and 6 in Scheme , employing mass selective threshold photoelectron spectroscopy (ms‐TPES) and obtained ionization energies (IE) of 7.70±0.02, 7.59±0.01 and 8.01±0.01 eV for 4 , 5 and 6 . In addition, a vibrational progression assigned to an in‐plane deformation mode of the aromatic ring was observed for all three of them …”

Nitrogen matters: the difference between PANH and PAH formation

“…42,43 Threshold photoelectron spectra of possible intermediates and products have been simulated employing the eZspectrum 44 and Gaussian16 software packages to allow for isomer-selective assignment. 31,32,45,46 Franck-Condon factors have been calculated at 400 to 500 K, which are typical final temperatures for species produced in hot pyrolysis reactors. 28,46 The stick spectra were subsequently convoluted with a 30-50 meV broad Gaussian function to account for the rotational envelope and to facilitate comparison with the experimental spectra.…”

“…31,32,45,46 Franck-Condon factors have been calculated at 400 to 500 K, which are typical final temperatures for species produced in hot pyrolysis reactors. 28,46 The stick spectra were subsequently convoluted with a 30-50 meV broad Gaussian function to account for the rotational envelope and to facilitate comparison with the experimental spectra. The adiabatic ionization energy is determined from the CBS-QB3 calculated energies of the neutral and ionic product species.…”