Laser Pump-Probe Experiments on Microsecond to Millisecond Timescales at an Electrostatic Ion Storage Ring: Triplet–Triplet Absorption by Protoporphyrin-IX Anions

Abstract

Here we demonstrate that pump-probe experiments can be carried out on microsecond to millisecond timescales using an electrostatic ion storage ring. As a test case, we have chosen protoporhyrin IX anions that have lifetimes with respect to dissociation after photoexcitation on this time scale. Ions were photoexcited on one side of the ring with either 430- or 535-nm light (pump) and then allowed to take a certain number of revolutions before they were photoexcited by a second laser pulse (probe) with wavelengths between 650 and 950 nm. If ions were first excited by the pump, an increased yield of neutral products caused by the absorption of red light was measured in a microchannel plate detector located on the other side of the ring. This implies that it is possible to pick out ions that were photoexcited by the pump pulse and to spectroscopically characterize these ions. We report absorption spectra of 535 nm photoexcited porphyrin anions, with time delays of 0.19 and 0.57 ms between the pump and probe pulses, and find that absorption occurs over a broad region in the red.