The low temperature fluorescence spectra (4.2 K) of solid solutions of pditluorobenzene-h., (pDFB-h.,) and-& have been recorded and analyzed. The absence of fluorescence from vibrationally excited states at 4.2 K eliminates the sequence and "hot band" structure which complicate the analysis of the vapor fluorescence spectrum. On the basis of a comparison of our vibrational analysis with those published for the vapor phase fluorescence, several incorrect assignments in the latter have been identified. The high resolution and lack of spectral congestion obtained in the low temperature matrix isolated fluorescence spectra also allowed additional vibrational assignments to be made. These results are of added importance because of the extensive use. which has been made of pDFR for radiationless relaxation studies in the vapor phase. The phosphorescence spectrum of crystalline pDFB-h, was observed with sufficient intensity to locate the electronic origin to make several vibrational assignments. Additionally, the zero-field splitting of the first triplet excited state was measured by optically detected magnetic resonance techniques.

The spectrum acquired at the sample photomultiplier tube of a fluorescence spectrophotometer is a product of the sample spectrum and the instrument function. The determination of the instrument function and its removal from the acquired spectrum is often critical to the accurate determination of the physical properties of the sample. Methods are discussed for the determination and removal of the instrument function from excitation and emission spectra. Methods considered include quantum counters and ratio circuits for excitation correction, and emission correction against calibrated excitation systems, calibrated tungsten lamps, and NBS standard quinine sulfate.

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