Probing the photoinduced Rydberg ionization process

The photophysical processes behind the new technique of photoinduced Rydberg ionization (PIRI) spectroscopy have been investigated for benzene. The major limitation to the signal-to-noise attainable using this method has been found to be caused by spontaneous autoionization of the prepared Rydbergs. In addition, some evidence has been found to suggest that the autoionizing transitions, which form the basis of the PIRI technique, only take place when the Rydberg electron is of lower n (and therefore I) than the typical n=100-200 employed in pulsed field ionization experiments. A new method of recording photoinduced ion core transitions, employing multiphoton photodissociation of the Rydberg core, is also reported. The lighter masses of the fragment ions enable them to be separated from the background of parent ions created by spontaneous autoionization. This method allows the core excitation transition to originate from a vibrationally excited state which previously had produced a prohibitively large background as a result of vibrational autoionization.