A photoabsorption and mass spectrometry study of pyrrole Original Research Article

The absolute photoabsorption cross-section of pyrrole has been measured between the ionisation threshold and 35 eV using a double ion chamber and monochromated synchrotron radiation. An interpretation has been proposed for some of the observed structure in terms of Rydberg series converging onto the à 2B1 state threshold. In addition, the possibility that several broad features may be attributed to π→π∗ transitions is discussed. Time-of-flight mass spectra have been recorded for excitation energies between 11.8 and 27.5 eV, and appearance energies have been determined for seventeen fragment ions and the doubly charged parent ion. These have enabled, previously unknown, heats of formation to be estimated for five ions, including the doubly charged parent ion. A high resolution mass spectrometer, equipped with an electron impact ionisation source, has been used in B/E and B2/E linked scanning modes to identify reactant/product pairings. Fragmentation processes leading to the production of several high intensity fragment ions have been modelled using ab initio and semi-empirical methods.