The evaluation of photochemical quantum yields by holography

Abstract

The recently developed holographic technique for the investigation of solid‐statephotochemical reactions is applied to the determination of photochemical quantum yields. An explicit formula is derived for the case of a simple one‐photon reaction which can be easily modified to handle more complicated reaction schemes. The only input parameters needed are the temporal growth curve of the photochemically formed hologram and the change in molar refraction. The last parameter can be obtained from the absorption spectra of educt and product species or from direct measurements of the index of refraction. The theory is applied to the phototransformation of o‐nitrobenzaldehyde in a polymethylmethacrylate matrix. The resulting quantum yield is compared to that obtained by a conventional absorptionspectroscopic procedure and found to be in good agreement. The advantages of the holographic technique compared to conventional absorption spectroscopy are discussed.