Transient vibrational echo versus transient absorption spectroscopy: a direct experimental and theoretical comparison.

Transient dispersed vibrational echo (DVE) spectroscopy is a practical alternative to transient-absorption spectroscopy because it affords increased sensitivity as well as greater signal-to-noise ratio without the need to detect a reference spectrum. However, as a third-order nonlinear probe, the extraction of kinetic information from transient-DVE is somewhat cumbersome compared to transient absorption. This article provides a direct experimental and theoretical comparison between transient-absorption and transient-DVE measurements and presents a framework for analyzing kinetic measurements while exploring the implications of making some simplifying assumptions in the data analysis. The equations for computing the signal-to-noise ratios under different experimental conditions are derived and used in the analysis of the experimental data. The results, obtained under the same experimental conditions, show that for a relatively strong terminal carbonyl stretching mode, signal-to-noise ratios in transient-DVE spectroscopy are approximately 2.5 times greater than transient absorption. The experimental results along with the theoretical models indicate that transient-DVE could become an attractive alternative to transient-absorption spectroscopy for measuring the kinetics of light-induced processes.