A photoacoustic detection system is described that has excellent linearity and limits of detection, and which is simple to implement. This system has been applied to the determination of intersystem crossing yields, Φ<sub><i>isc</i></sub>, of a series of Cr(NN)<sub>3</sub><sup>3+</sup> complexes. The results are in excellent agreement with the literature values for two of these complexes. Results for two other complexes determined that there are long-lived (τ > 15 ns) upper excited states or other high-energy species produced that prevent rapid relaxation to the lowest energy excited state of these complexes. Without the need to resort to deconvolution techniques, this method can be used on systems that have rapid relaxation (τ < 1 ns) of the upper excited states and lifetimes >5 μs for the lowest energy excited state, with the application of a 5 MHz piezoelectric transducer.
Daniel Lynch and John F. Endicott, "A Pulsed Photoacoustic Microcalorimeter for the Detection of Upper Excited-State Processes and Intersystem Crossing Yields," Appl. Spectrosc. 43, 826-833 (1989)