Optimization of a pulse laser spectrometer for the measurement of the kinetics of singlet oxygen O2(delta 1g) decay in solution.

A simple sensitive pulse laser spectrometer to measure the kinetics of singlet oxygen decay in solution is described. It utilizes a NdYag laser for pulse excitation of the 1O2 photosensitizers perinaphthenone and Rose Bengal or eosine at 355 nm and 532 nm, respectively. Singlet oxygen phosphorescence is detected by a germanium diode, to which collimated phosphorescence light is directed by concave and parabolic mirrors via a pair of Fresnel lenses and an infrared interference filter. The 1O2 transient decays are monitored using a Hewlett Packard digitizing oscilloscope and a PC computer. The excellent sensitivity of this spectrometer allows us to easily observe 1O2 decay (1 microsecond resolution) after a single pulse of laser excitation, which is important for quenching measurements of chemical substrates that react readily with 1O2. The small sample volume (0.1 ml) prepared in quartz tubes permits fast and inexpensive data acquisition for the determination of 1O2 quenching rate constants in most solvents.