Pyrolysis of 3-Methoxypyridine. Detection and Characterization of the Pyrrolyl Radical by Threshold Photoelectron Spectroscopy

Abstract

Pyrolysis of 3-methoxypyridine in a heated pyrolysis reactor was found to be an efficient way to generate the pyrrolyl radical, c-C4H4N, in the gas phase. The threshold photoelectron (TPE) spectrum of this radical was recorded using vacuum ultraviolet synchrotron radiation. The spectrum revealed a singlet ground state at 9.11 ± 0.02 eV (X̃(+ 1)A) and an excited triplet state (ã(+ 3)A) at 9.43 ± 0.05 eV. Vibrational structure was observed for both cationic states and could be assigned to ring deformation modes. Furthermore, (E)- and (Z)-1-cyanoallyl radicals were found to contribute to the TPE spectrum below 8.9 eV. In addition, we have identified two parallel decomposition channels of the pyrrolyl radical, yielding either hydrogen cyanide and propargyl radical or acetylene and cyanomethyl radical. The reaction energy profiles have also been calculated for these reactions. In addition, the dissociative photoionization of the precursor 3-methoxypyridine is reported.