A Flash Kinetic Spectrophotometer Employing Photodiode Array Sensors

We are describing a method for rapid spectroscopic measurement of phototransients obtained in a flash photolysis apparatus. A linear photodiode array is employed as a detector to sense changes in light absorption across the visible spectrum. A microcomputer handles sampling, analysis, and plotting the data, and controls a xenon flash photolysis unit. This approach provides simultaneous wavelength acquisition compatible with millisecond time scales. The implementation described here monitors 22 wavelengths over a 300 nm range with up to 50 consecutive spectral scans spaced a minimum of 0.5 ms. Wavelength and temporal resolution, set by spectrograph and detector exposure period, are 1.5 nm and 0.5 ms. The main advantages of this method are collection of multiwavelength data for determining complex transient spectral changes with little sample, and convenience of both data acquisition and analysis. Application to measurements of bacterial rhodopsin photochemistry is described.