The secondary response distortion in transient absorption spectroscopy

Transient absorption spectroscopy has been used for many years to record the kinetics and spectra of transient chemical species following a short photolysis or radiation pulse. Linearity of the detector is always important, but cannot always be assumed for experiments on a submicrosecond timescale, and should never be assumed on a subnanosecond timescale. In addition, fast photodiode detectors often exhibit a delayed secondary response, which depends on the wavelength of excitation. In this article we demonstrate the distortions introduced by secondary detector response with some examples from pulse radiolysis. A method for calibration is demonstrated using the broad visible/near-infrared absorption of solvated electrons in water. A standard decay shape is constructed from stroboscopic measurements at short time, and from the (400-800 nm) response of an EG&G FND100Q silicon diode at times greater than 10 ns. The calibration is applied to the FND100Q silicon diode, and to GMP566 germanium and GAP520 InGaAs diodes manufactured by Germanium Power Devices, Inc. Correction of the latter diode is needed to record a visible/near infrared spectrum of solvated electrons in heavy water at elevated temperatures. (C) 2002 American Institute of Physics.