Method for acquiring extended real-time kinetic signals in nanosecond laser flash photolysis experiments

We report a data acquisition method for detecting transient absorbance signals extended in time which require nanosecond resolution and need to span several decades in time up to the hundreds of milliseconds. A microprocessor is used to generate a sequence of up to 100, 2.120 mus wide radio frequency signals at 500 MHz which are used to trigger the analog-to-digital conversion on a digital oscilloscope, operating in the external clock mode. During these radio frequency bursts the data are sampled at a sampling rate of 500 Ms/s. The delay of each sampling burst can be set at arbitrary values with respect to the first signal, with a minimum delay of 0.96 mus for the second pulse, and 1.2 mus for all other pulses. The microprocessor provides accessory synchronization outputs for laser triggering and for shutter opening and closing. This data acquisition system allows measuring the complete time course of extended kinetics after each laser shot, thus reducing acquisition times and data size. We prove the complete equivalence of the proposed acquisition method with standard methods, where several time bases are acquired to cover the complete kinetic trace for the ligand rebinding to myoglobin after photolysis of a gel embedded myoglobin-CO complex. (C) 2004 American Institute of Physics.